HKU Scholars Hubhttp://hub.hku.hkThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Wed, 19 May 2021 03:43:29 GMT2021-05-19T03:43:29Z50831- Coulomb Liquid Phases of Bosonic Cluster Mott Insulators on a Pyrochlore Latticehttp://hdl.handle.net/10722/266130Title: Coulomb Liquid Phases of Bosonic Cluster Mott Insulators on a Pyrochlore Lattice
Authors: Lv, Jian Ping; Chen, Gang; Deng, Youjin; Meng, Zi Yang
Abstract: © 2015 American Physical Society. © 2015 American Physical Society. Employing large-scale quantum Monte Carlo simulations, we reveal the full phase diagram of the extended Hubbard model of hard-core bosons on the pyrochlore lattice with partial fillings. When the intersite repulsion is dominant, the system is in a cluster Mott insulator phase with an integer number of bosons localized inside the tetrahedral units of the pyrochlore lattice. We show that the full phase diagram contains three cluster Mott insulator phases with 1/4, 1/2, and 3/4 boson fillings, respectively. We further demonstrate that all three cluster Mott insulators are Coulomb liquid phases and its low-energy property is described by the emergent compact U(1) quantum electrodynamics. In addition to measuring the specific heat and entropy of the cluster Mott insulators, we investigate the correlation function of the emergent electric field and verify it is consistent with the compact U(1) quantum electrodynamics description. Our result sheds light on the magnetic properties of various pyrochlore systems, as well as the charge physics of the cluster magnets.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10722/2661302015-01-01T00:00:00Z
- Monte Carlo Study of Lattice Compact Quantum Electrodynamics with Fermionic Matter: The Parent State of Quantum Phaseshttp://hdl.handle.net/10722/270102Title: Monte Carlo Study of Lattice Compact Quantum Electrodynamics with Fermionic Matter: The Parent State of Quantum Phases
Authors: Xu, XY; Qi, Y; Zhang, L; Assaad, FF; Xu, CK; Meng, Z
Abstract: The interplay between lattice gauge theories and fermionic matter accounts for fundamental physical phenomena ranging from the deconfinement of quarks in particle physics to quantum spin liquid with fractionalized anyons and emergent gauge structures in condensedmatter physics. However, except for certain limits (for instance, a large number of flavors of matter fields), analytical methods can provide few concrete results. Here we show that the problem of compact U(1) lattice gauge theory coupled to fermionic matter in (2+1) D is possible to access via sign-problem-free quantum Monte Carlo simulations. One can hence map out the phase diagramas a function of fermion flavors and the strength of gauge fluctuations. By increasing the coupling constant of the gauge field, gauge confinement in the form of various spontaneous-symmetry-breaking phases such as the valence-bond solid (VBS) and Neel antiferromagnet emerge. Deconfined phases with algebraic spin and VBS correlation functions are also observed. Such deconfined phases are incarnations of exotic states of matter, i.e., the algebraic spin liquid, which is generally viewed as the parent state of various quantum phases. The phase transitions between the deconfined and confined phases, as well as that between the different confined phases provide various manifestations of deconfined quantum criticality. In particular, for four flavors N-f = 4, our data suggest a continuous quantum phase transition between the VBS and Neel order. We also provide preliminary theoretical analysis for these quantum phase transitions.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/10722/2701022019-01-01T00:00:00Z
- Correlated states in twisted double bilayer graphenehttp://hdl.handle.net/10722/285491Title: Correlated states in twisted double bilayer graphene
Authors: Shen, C; Chu, Y; Wu, Q; Li, N; Wang, S; Zhao, Y; Tang, J; Liu, J; Tian, J; Watanabe, K; Taniguchi, T; Yang, R; Meng, ZY; Shi, D; Yazyev, OV; Zhang, G
Abstract: Electron–electron interactions play an important role in graphene and related systems and can induce exotic quantum states, especially in a stacked bilayer with a small twist angle1,2,3,4,5,6,7. For bilayer graphene where the two layers are twisted by the ‘magic angle’, flat band and strong many-body effects lead to correlated insulating states and superconductivity4,5,6,7. In contrast to monolayer graphene, the band structure of untwisted bilayer graphene can be further tuned by a displacement field8,9,10, providing an extra degree of freedom to control the flat band that should appear when two bilayers are stacked on top of each other. Here, we report the discovery and characterization of displacement field-tunable electronic phases in twisted double bilayer graphene. We observe insulating states at a half-filled conduction band in an intermediate range of displacement fields. Furthermore, the resistance gap in the correlated insulator increases with respect to the in-plane magnetic fields and we find that the g factor, according to the spin Zeeman effect, is ~2, indicating spin polarization at half-filling. These results establish twisted double bilayer graphene as an easily tunable platform for exploring quantum many-body states.
Wed, 01 Jan 2020 00:00:00 GMThttp://hdl.handle.net/10722/2854912020-01-01T00:00:00Z
- Quantum Phases of SrCu2(BO3)2 from High-Pressure Thermodynamicshttp://hdl.handle.net/10722/285492Title: Quantum Phases of SrCu2(BO3)2 from High-Pressure Thermodynamics
Authors: Guo, J; Sun, G; Zhao, B; Wang, L; Hong, W; Sidorov, VA; Ma, N; Wu, Q; Li, SL; Meng, ZY; Sandvik, AW; Sun, L
Abstract: We report heat capacity measurements of SrCu2(BO3)2 under high pressure along with simulations of relevant quantum spin models and map out the (P,T) phase diagram of the material. We find a first-order quantum phase transition between the low-pressure quantum dimer paramagnet and a phase with signatures of a plaquette-singlet state below T=2 K. At higher pressures, we observe a transition into a previously unknown antiferromagnetic state below 4 K. Our findings can be explained within the two-dimensional Shastry-Sutherland quantum spin model supplemented by weak interlayer couplings. The possibility to tune SrCu2(BO3)2 between the plaquette-singlet and antiferromagnetic states opens opportunities for experimental tests of quantum field theories and lattice models involving fractionalized excitations, emergent symmetries, and gauge fluctuations.
Wed, 01 Jan 2020 00:00:00 GMThttp://hdl.handle.net/10722/2854922020-01-01T00:00:00Z
- Confinement transition in the QED3-Gross-Neveu-XY universality classhttp://hdl.handle.net/10722/285489Title: Confinement transition in the QED3-Gross-Neveu-XY universality class
Authors: Janssen, L; Wang, W; Scherer, MM; Meng, ZY; Xu, XY
Abstract: The coupling between fermionic matter and gauge fields plays a fundamental role in our understanding of nature, while at the same time posing a challenging problem for theoretical modeling. In this situation, controlled information can be gained by combining different complementary approaches. Here, we study a confinement transition in a system of Nf flavors of interacting Dirac fermions charged under a U(1) gauge field in 2+1 dimensions. Using quantum Monte Carlo simulations, we investigate a lattice model that exhibits a continuous transition at zero temperature between a gapless deconfined phase, described by three-dimensional quantum electrodynamics, and a gapped confined phase, in which the system develops valence-bond-solid order. We argue that the quantum critical point is in the universality class of the QED3-Gross-Neveu-XY model. We study this field theory within a 1/Nf expansion in fixed dimension as well as a renormalization group analysis in 4-ϵ space-time dimensions. The consistency between numerical and analytical results is revealed from large to intermediate flavor number.
Wed, 01 Jan 2020 00:00:00 GMThttp://hdl.handle.net/10722/2854892020-01-01T00:00:00Z
- Designer Monte Carlo simulation for the Gross-Neveu-Yukawa transitionhttp://hdl.handle.net/10722/286294Title: Designer Monte Carlo simulation for the Gross-Neveu-Yukawa transition
Authors: Liu, Y; Wang, W; Sun, K; Meng, ZY
Abstract: In this paper, we study the quantum criticality of Dirac fermions via large-scale numerical simulations, focusing on the Gross-Neveu-Yukawa chiral-Ising quantum critical point (QCP) with critical bosonic modes coupled with Dirac fermions. We show that finite-size effects at this QCP can be efficiently minimized via model design, which maximizes the ultraviolet cutoff and at the same time places the bare control parameters closer to the nontrivial fixed point to better expose the critical region. Combined with the efficient self-learning quantum Monte Carlo algorithm, which enables a nonlocal update of the bosonic field, we find that moderately large system size (up to 16×16) is already sufficient to produce robust scaling behavior and critical exponents. The conductance of free Dirac fermions is also calculated, and its frequency dependence is found to be consistent with the scaling behavior predicted by the conformal field theory. The methods and model-design principles developed for this study can be generalized to other fermionic QCPs, and thus provide a promising direction for controlled studies of strongly correlated itinerant systems.
Wed, 01 Jan 2020 00:00:00 GMThttp://hdl.handle.net/10722/2862942020-01-01T00:00:00Z
- Revealing fermionic quantum criticality from new Monte Carlo techniqueshttp://hdl.handle.net/10722/276341Title: Revealing fermionic quantum criticality from new Monte Carlo techniques
Authors: Xu, XY; Liu, ZH; Pan, GP; Qi, Y; Sun, K; Meng, Z
Abstract: This review summarizes recent developments in the study of fermionic quantum criticality, focusing on new progress in numerical methodologies, especially quantum Monte Carlo methods, and insights that emerged from recently large-scale numerical simulations. Quantum critical phenomena in fermionic systems have attracted decades of extensive research efforts, partially lured by their exotic properties and potential technology applications, and partially awakened by the profound and universal fundamental principles that govern these quantum critical systems. Due to the complex and non-perturbative nature, these systems face the most difficult and challenging problems in the study of modern condensed matter physics, and many important fundamental problems remain open. Recently, new developments in model design and algorithm improvements enabled unbiased large-scale numerical solutions to be achieved in the close vicinity of these quantum critical points, which paves a new pathway towards achieving controlled conclusions through combined efforts of theoretical and numerical studies, as well as possible theoretical guidance for experiments in heavy-fermion compounds, Cu-based and Fe-based superconductors, ultra-cold fermionic atomic gas, twisted graphene layers, etc, where signatures of fermionic quantum criticality exist.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/10722/2763412019-01-01T00:00:00Z
- Quantum Monte Carlo study of strange correlator in interacting topological insulatorshttp://hdl.handle.net/10722/268475Title: Quantum Monte Carlo study of strange correlator in interacting topological insulators
Authors: Wu, Han Qing; He, Yuan Yao; You, Yi Zhuang; Xu, Cenke; Meng, Zi Yang; Lu, Zhong Yi
Abstract: © 2015 American Physical Society. Distinguishing the nontrivial symmetry-protected topological (SPT) phase from the trivial insulator phase in the presence of electron-electron interaction is an urgent question to the study of topological insulators, due to the fact that most of the topological indices defined for free electron systems are very likely unsuitable for interacting cases. In this work, we demonstrate that the strange correlator is a sensitive diagnosis to detect SPT states in interacting systems. Employing large-scale quantum Monte Carlo (QMC) simulations, we investigate the interaction-driven quantum phase transition in the Kane-Mele-Hubbard model. The transition from the quantum spin Hall insulator at weak interaction to an antiferromagnetic Mott insulator at strong interaction can be readily detected by the momentum space behavior of the strange correlator in single-particle, spin, and pairing sectors. The interaction effects on the symmetry-protected edge states in various sectors, i.e., the helical Luttinger liquid behavior, are well captured in the QMC measurements of strange correlators. Moreover, we demonstrate that the strange correlator is technically easier to implement in QMC and more robust in performance than other proposed numerical diagnoses for interacting topological states, as only static correlations are needed. The attempt in this work paves the way for using the strange correlator to study interaction-driven topological phase transitions in fermionic as well as bosonic systems.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10722/2684752015-01-01T00:00:00Z
- Mott insulating states and quantum phase transitions of correlated SU(2N) Dirac fermionshttp://hdl.handle.net/10722/268581Title: Mott insulating states and quantum phase transitions of correlated SU(2N) Dirac fermions
Authors: Zhou, Zhichao; Wang, Da; Meng, Zi Yang; Wang, Yu; Wu, Congjun
Abstract: © 2016 American Physical Society. The interplay between charge and spin degrees of freedom in strongly correlated fermionic systems, in particular of Dirac fermions, is a long-standing problem in condensed matter physics. We investigate the competing orders in the half-filled SU(2N) Hubbard model on a honeycomb lattice, which can be accurately realized in optical lattices with ultracold large-spin alkaline-earth fermions. Employing large-scale projector determinant quantum Monte Carlo simulations, we have explored quantum phase transitions from the gapless Dirac semimetals to the gapped Mott insulating phases in the SU(4) and SU(6) cases. Both of these Mott insulating states are found to be columnar valence bond solid (cVBS) and to be absent of the antiferromagnetic Néel ordering and the loop current ordering. Inside the cVBS phases, the dimer ordering is enhanced by increasing fermion components and behaves nonmonotonically as the interaction strength increases. Although the transitions generally should be of first order due to a cubic invariance possessed by the cVBS order, the coupling to gapless Dirac fermions can soften the transitions to second order through a nonanalytic term in the free energy. Our simulations provide important guidance for the experimental explorations of novel states of matter with ultracold alkaline-earth fermions.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10722/2685812016-01-01T00:00:00Z
- Diagnosis of Interaction-driven Topological Phase via Exact Diagonalizationhttp://hdl.handle.net/10722/268583Title: Diagnosis of Interaction-driven Topological Phase via Exact Diagonalization
Authors: Wu, Han Qing; He, Yuan Yao; Fang, Chen; Meng, Zi Yang; Lu, Zhong Yi
Abstract: © 2016 American Physical Society. We propose a general scheme for diagnosing interaction-driven topological phases in the weak interaction regime using exact diagonalization (ED). The scheme comprises the analysis of eigenvalues of the point-group operators for the many-body eigenstates and the correlation functions for physical observables to extract the symmetries of the order parameters and the topological numbers of the underlying ground states at the thermodynamic limit from a relatively small size system afforded by ED. As a concrete example, we investigate the interaction effects on the half-filled spinless fermions on the checkerboard lattice with a quadratic band crossing point. Numerical results support the existence of a spontaneous quantum anomalous Hall phase purely driven by a nearest-neighbor weak repulsive interaction, separated from a nematic Mott insulator phase at strong repulsive interaction by a first-order phase transition.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10722/2685832016-01-01T00:00:00Z
- Competing pairing channels in the doped honeycomb lattice Hubbard modelhttp://hdl.handle.net/10722/268584Title: Competing pairing channels in the doped honeycomb lattice Hubbard model
Authors: Xu, Xiao Yan; Wessel, Stefan; Meng, Zi Yang
Abstract: © 2016 American Physical Society. Proposals for superconductivity emerging from correlated electrons in the doped Hubbard model on the honeycomb lattice range from chiral d+id singlet to p+IP trIPlet pairing, depending on the considered range of doping and interaction strength, as well as the approach used to analyze the pairing instabilities. Here, we consider these scenarios using large-scale dynamic cluster approximation (DCA) calculations to examine the evolution in the leading pairing symmetry from weak to intermediate coupling strength. These calculations focus on doping levels around the van Hove singularity (VHS) and are performed using DCA simulations with an interaction-expansion continuous-time quantum Monte Carlo cluster solver. We calculated explicitly the temperature dependence of different uniform superconducting pairing susceptibilities and found a consistent picture emerging upon gradually increasing the cluster size: while at weak coupling the d+id singlet pairing dominates close to the VHS filling, an enhanced tendency towards p-wave trIPlet pairing upon further increasing the interaction strength is observed. The relevance of these systematic results for existing proposals and ongoing pursuits of odd-parity topological superconductivity are also discussed.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10722/2685842016-01-01T00:00:00Z
- Quantum critical point of Dirac fermion mass generation without spontaneous symmetry breakinghttp://hdl.handle.net/10722/268632Title: Quantum critical point of Dirac fermion mass generation without spontaneous symmetry breaking
Authors: He, Yuan Yao; Wu, Han Qing; You, Yi Zhuang; Xu, Cenke; Meng, Zi Yang; Lu, Zhong Yi
Abstract: © 2016 American Physical Society. We study a lattice model of interacting Dirac fermions in (2+1) dimensions space-time with an SU(4) symmetry. While increasing the interaction strength, this model undergoes a continuous quantum phase transition from a weakly interacting Dirac semimetal to a fully gapped and nondegenerate phase without condensing any Dirac fermion bilinear mass operator. This unusual mechanism for mass generation is consistent with recent studies of interacting topological insulators/superconductors, and also consistent with recent progress in the lattice QCD community.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10722/2686322016-01-01T00:00:00Z
- Gapped Spin-1/2 Spinon Excitations in a New Kagome Quantum Spin Liquid Compound Cu3Zn(OH)6FBrhttp://hdl.handle.net/10722/268647Title: Gapped Spin-1/2 Spinon Excitations in a New Kagome Quantum Spin Liquid Compound Cu3Zn(OH)6FBr
Authors: Feng, Zili; Li, Zheng; Meng, Xin; Yi, Wei; Wei, Yuan; Zhang, Jun; Wang, Yan Cheng; Jiang, Wei; Liu, Zheng; Li, Shiyan; Liu, Feng; Luo, Jianlin; Li, Shiliang; Zheng, Guo Qing; Meng, Zi Yang; Mei, Jia Wei; Shi, Youguo
Abstract: © 2017 Chinese Physical Society and IOP Publishing Ltd. We report a new kagome quantum spin liquid candidate Cu 3 Zn(OH) 6 FBr, which does not experience any phase transition down to 50 mK, more than three orders lower than the antiferromagnetic Curie-Weiss temperature (∼200 K). A clear gap opening at low temperature is observed in the uniform spin susceptibility obtained from 19 F nuclear magnetic resonance measurements. We observe the characteristic magnetic field dependence of the gap as expected for fractionalized spin-1/2 spinon excitations. Our experimental results provide firm evidence for spin fractionalization in a topologically ordered spin system, resembling charge fractionalization in the fractional quantum Hall state.
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/10722/2686472017-01-01T00:00:00Z
- Non-fermi liquid at (2 + 1)D ferromagnetic quantum critical pointhttp://hdl.handle.net/10722/268597Title: Non-fermi liquid at (2 + 1)D ferromagnetic quantum critical point
Authors: Xu, Xiao Yan; Sun, Kai; Schattner, Yoni; Berg, Erez; Meng, Zi Yang
Abstract: We construct a two-dimensional lattice model of fermions coupled to Ising ferromagnetic critical fluctuations. Using extensive sign-problem-free quantum Monte Carlo simulations, we show that the model realizes a continuous itinerant quantum phase transition. In comparison with other similar itinerant quantum critical points (QCPs), our QCP shows a much weaker superconductivity tendency with no superconducting state down to the lowest temperature investigated, hence making the system a good platform for the exploration of quantum critical fluctuations. Remarkably, clear signatures of non-Fermi liquid behavior in the fermion propagators are observed at the QCP. The critical fluctuations at the QCP partially resemble Hertz-Millis-Moriya behavior. However, careful scaling analysis reveals that the QCP belongs to a different universality class, deviating from both ð2 þ 1ÞD Ising and Hertz-Millis-Moriya predictions.
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/10722/2685972017-01-01T00:00:00Z
- Quantum spin liquid emerging in two-dimensional correlated Dirac fermionshttp://hdl.handle.net/10722/268517Title: Quantum spin liquid emerging in two-dimensional correlated Dirac fermions
Authors: Meng, Z. Y.; Lang, T. C.; Wessel, S.; Assaad, F. F.; Muramatsu, A.
Abstract: At sufficiently low temperatures, condensed-matter systems tend to develop order. A notable exception to this behaviour is the case of quantum spin liquids, in which quantum fluctuations prevent a transition to an ordered state down to the lowest temperatures. There have now been tentative observations of such states in some two-dimensional organic compounds, yet quantum spin liquids remain elusive in microscopic two-dimensional models that are relevant to experiments. Here we show, by means of large-scale quantum Monte Carlo simulations of correlated fermions on a honeycomb lattice (a structure realized in, for example, graphene), that a quantum spin liquid emerges between the state described by massless Dirac fermions and an antiferromagnetically ordered Mott insulator. This unexpected quantum-disordered state is found to be a short-range resonating valence-bond liquid, akin to the one proposed for high-temperature superconductors: the possibility of unconventional superconductivity through doping therefore arises in our system. We foresee the experimental realization of this model system using ultra-cold atoms, or group IV elements arranged in honeycomb lattices. © 2010 Macmillan Publishers Limited. All rights reserved.
Fri, 01 Jan 2010 00:00:00 GMThttp://hdl.handle.net/10722/2685172010-01-01T00:00:00Z
- A quantum spin-liquid in correlated relativistic electronshttp://hdl.handle.net/10722/268637Title: A quantum spin-liquid in correlated relativistic electrons
Authors: Meng, Z. Y.; Lang, T. C.; Wessel, S.; Assaad, F. F.; Muramatsu, A.
Abstract: In recent years, an increasing number of systems displaying exotic quantum states like unconventional superconductivity, quantum spin-liquids, or topological states were experimentally found. Here we summarize findings in quantum Monte Carlo simulations of correlated electrons on a honeycomb lattice, the structure of graphene, that revealed an unexpected spin-liquid emerging between a state described by massless Dirac fermions and an antiferromagnetically ordered Mott insulator. Moreover, we found that this quantum-disordered state is a resonating valence-bond (RVB) liquid, akin to the one proposed for high temperature superconductors. This was the first unbiased determination of a RVB-liquid in an electronic system. © 2012 by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/10722/2686372012-01-01T00:00:00Z
- Dual fermion method for disordered electronic systemshttp://hdl.handle.net/10722/268654Title: Dual fermion method for disordered electronic systems
Authors: Terletska, H.; Yang, S. X.; Meng, Z. Y.; Moreno, J.; Jarrell, M.
Abstract: While the coherent potential approximation (CPA) is the prevalent method for the study of disordered electronic systems, it fails to capture nonlocal correlations and Anderson localization. To incorporate such effects, we extend the dual fermion approach to disordered systems using the replica method. The developed method utilizes the exact mapping to the dual fermion variables, and includes intersite scattering via diagrammatic perturbation theory in the dual variables. The CPA is recovered as a zeroth-order approximation. Results for single- and two-particle quantities show good agreement with a cluster extension of the CPA; moreover, weak localization is captured. As a natural extension of the CPA, our method presents an alternative to existing nonlocal cluster theories for disordered systems, and has potential applications in the study of disordered systems with electronic interactions. © 2013 American Physical Society.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10722/2686542013-01-01T00:00:00Z
- Spin-liquid phase in the hubbard model on the honeycomb latticehttp://hdl.handle.net/10722/268547Title: Spin-liquid phase in the hubbard model on the honeycomb lattice
Authors: Meng, Z. Y.; Lang, T. C.; Wessel, S.; Assaad, F. F.; Muramatsu, A.
Abstract: The Hubbard model encapsulates the physics of strongly correlated quantum systems in its most basic form. It has been studied intensively in the context of the high-temperature superconductivity. A number of novel phases were recently proposed for Hubbard-like models on the honeycomb lattice, the structure of graphene. We analyzed the Hubbard model of spin-1/2 fermions on the honeycomb lattice at half-filling using large-scale quantum Monte Carlo simulations. We find that the weak coupling semimetal and the antiferromagnetic Mott insulator at strong interaction are separated by an extended gapped phase in an intermediate coupling regime. Exploring excitation gaps, various correlation functions as well as probing for flux quantization, we conclude that a quantum spin liquid, lacking any conventional order, emerges with local charge and spin correlations, best described by a resonating valence bonds state. © Springer-Verlag Berlin Heidelberg 2011.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10722/2685472011-01-01T00:00:00Z
- Typical medium dynamical cluster approximation for the study of Anderson localization in three dimensionshttp://hdl.handle.net/10722/268472Title: Typical medium dynamical cluster approximation for the study of Anderson localization in three dimensions
Authors: Ekuma, C. E.; Terletska, H.; Tam, K. M.; Meng, Z. Y.; Moreno, J.; Jarrell, M.
Abstract: We develop a systematic typical medium dynamical cluster approximation that provides a proper description of the Anderson localization transition in three dimensions (3D). Our method successfully captures the localization phenomenon both in the low and large disorder regimes, and allows us to study the localization in different momenta cells, which renders the discovery that the Anderson localization transition occurs in a cell-selective fashion. As a function of cluster size, our method systematically recovers the reentrance behavior of the mobility edge and obtains the correct critical disorder strength for Anderson localization in 3D. © 2014 American Physical Society.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10722/2684722014-01-01T00:00:00Z
- Odd-Parity triplet superconducting phase in multiorbital materials with a strong spin-orbit coupling: Application to doped Sr2IrO4http://hdl.handle.net/10722/268560Title: Odd-Parity triplet superconducting phase in multiorbital materials with a strong spin-orbit coupling: Application to doped Sr2IrO4
Authors: Meng, Zi Yang; Kim, Yong Baek; Kee, Hae Young
Abstract: © 2014 American Physical Society. We explore possible superconducting states in t2g multiorbital correlated electron systems with strong spin-orbit coupling (SOC). In order to study such systems in a controlled manner, we employ large-scale dynamical mean-field theory (DMFT) simulations with the hybridization expansion continuous-time quantum Monte Carlo (CTQMC) impurity solver. To determine the pairing symmetry, we go beyond the local DMFT formalism using parquet equations to introduce the momentum dependence in the two-particle vertex and correlation functions. In the strong SOC limit, a singlet, d-wave pairing state in the electron-doped side of the phase diagram is observed at weak Hund's coupling, which is triggered by antiferromagnetic fluctuations. When the Hund's coupling is comparable to SOC, a twofold degenerate, triplet p-wave pairing state with relatively high transition temperature emerges in the hole-doped side of the phase diagram, which is associated with enhanced charge fluctuations. Experimental implications to doped Sr2IrO4 are discussed.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10722/2685602014-01-01T00:00:00Z
- iQIST: An open source continuous-time quantum Monte Carlo impurity solver toolkithttp://hdl.handle.net/10722/268572Title: iQIST: An open source continuous-time quantum Monte Carlo impurity solver toolkit
Authors: Huang, Li; Wang, Yilin; Meng, Zi Yang; Du, Liang; Werner, Philipp; Dai, Xi
Abstract: © 2015 Elsevier B.V. All rights reserved. Quantum impurity solvers have a broad range of applications in theoretical studies of strongly correlated electron systems. Especially, they play a key role in dynamical mean-field theory calculations of correlated lattice models and realistic materials. Therefore, the development and implementation of efficient quantum impurity solvers is an important task. In this paper, we present an open source interacting quantum impurity solver toolkit (dubbed iQIST). This package contains several highly optimized quantum impurity solvers which are based on the hybridization expansion continuous-time quantum Monte Carlo algorithm, as well as some essential pre- and post-processing tools. We first introduce the basic principle of continuous-time quantum Monte Carlo algorithm and then discuss the implementation details and optimization strategies. The software framework, major features, and installation procedure for iQIST are also explained. Finally, several simple tutorials are presented in order to demonstrate the usage and power of iQIST.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10722/2685722015-01-01T00:00:00Z
- Dynamical generation of topological masses in Dirac fermionshttp://hdl.handle.net/10722/268486Title: Dynamical generation of topological masses in Dirac fermions
Authors: He, Yuan Yao; Xu, Xiao Yan; Sun, Kai; Assaad, Fakher F.; Meng, Zi Yang; Lu, Zhong Yi
Abstract: © 2018 American Physical Society. We report the discovery of a topological Mott insulator in strongly correlated Dirac semimetals. Such an interaction-driven topological state has been theoretically proposed and is observed here with unbiased large-scale numerical simulations. In our model, interactions between electrons are mediated by Ising spins in a transverse field. The results indicate that the topological mass term is dynamically generated and the resulting quantum phase transition belongs to the (two-plus-one-dimensional) N=8 chiral Ising universality class. These conclusions stem from large-scale sign-free quantum Monte Carlo simulations.
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/10722/2684862018-01-01T00:00:00Z
- Itinerant quantum critical point with frustration and a non-Fermi liquidhttp://hdl.handle.net/10722/268601Title: Itinerant quantum critical point with frustration and a non-Fermi liquid
Authors: Liu, Zi Hong; Xu, Xiao Yan; Qi, Yang; Sun, Kai; Meng, Zi Yang
Abstract: © 2018 American Physical Society. Employing the self-learning quantum Monte Carlo algorithm, we investigate the frustrated transverse-field triangle-lattice Ising model coupled to a Fermi surface. Without fermions, the spin degrees of freedom undergo a second-order quantum phase transition between paramagnetic and clock-ordered phases. This quantum critical point (QCP) has an emergent U(1) symmetry and thus belongs to the (2+1)D XY universality class. In the presence of fermions, spin fluctuations introduce effective interactions among fermions and distort the bare Fermi surface towards an interacting one with hot spots and Fermi pockets. Near the QCP, non-Fermi-liquid behaviors are observed at the hot spots, and the QCP is rendered into a different universality with Hertz-Millis-type exponents. The detailed properties of this QCP and possibly related experimental systems are also discussed.
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/10722/2686012018-01-01T00:00:00Z
- Effect of Zn doping on the antiferromagnetism in kagome Cu4-xZnx(OH)6FBrhttp://hdl.handle.net/10722/268608Title: Effect of Zn doping on the antiferromagnetism in kagome Cu4-xZnx(OH)6FBr
Authors: Feng, Zili; Wei, Yuan; Liu, Ran; Yan, Dayu; Wang, Yan Cheng; Luo, Jianlin; Senyshyn, Anatoliy; Cruz, Clarina Dela; Yi, Wei; Mei, Jia Wei; Meng, Zi Yang; Shi, Youguo; Li, Shiliang
Abstract: © 2018 American Physical Society. Barlowite Cu4(OH)6FBr shows three-dimensional (3D) long-range antiferromagnetism, which is fully suppressed in Cu3Zn(OH)6FBr with a kagome quantum spin liquid ground state. Here we report systematic studies on the evolution of magnetism in the Cu4-xZnx(OH)6FBr system as a function of x to bridge the two limits of Cu4(OH)6FBr(x=0) and Cu3Zn(OH)6FBr(x=1). Neutron-diffraction measurements reveal a hexagonal-to-orthorhombic structural change with decreasing temperature in the x=0 sample. While confirming the 3D antiferromagnetic nature of low-temperature magnetism, the magnetic moments on some Cu2+ sites on the kagome planes are found to be vanishingly small, suggesting strong frustration already exists in barlowite. Substitution of interlayer Cu2+ with Zn2+ with gradually increasing x completely suppresses the bulk magnetic order at around x=0.4 but leaves a local secondary magnetic order up to x∼0.8 with a slight decrease in its transition temperature. The high-temperature magnetic susceptibility and specific-heat measurements further suggest that the intrinsic magnetic properties of kagome spin liquid planes may already appear from x>0.3 samples. Our results reveal that the Cu4-xZnx(OH)6FBr may be the long-thought experimental playground for the systematic investigations of the quantum phase transition from a long-range antiferromagnet to a topologically ordered quantum spin liquid.
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/10722/2686082018-01-01T00:00:00Z
- Emergent symmetry and conserved current at a one-dimensional incarnation of deconfined quantum critical pointhttp://hdl.handle.net/10722/278599Title: Emergent symmetry and conserved current at a one-dimensional incarnation of deconfined quantum critical point
Authors: Huang, RZ; Lu, DC; You, YZ; Meng, ZY; Xiang, T
Abstract: The deconfined quantum critical point (DQCP) was originally proposed as a continuous transition between two spontaneous symmetry breaking phases in 2D spin-1/2 systems. While great efforts have been spent on the DQCP for 2D systems, both theoretically and numerically, ambiguities among the nature of the transition are still not completely clarified. Here we shift the focus to a recently proposed 1D incarnation of DQCP in a spin-1/2 chain. By solving it with the variational matrix product state in the thermodynamic limit, a continuous transition between a valence-bond solid phase and a ferromagnetic phase is discovered. The scaling dimensions of various operators are calculated and compared with those from field theoretical description. At the critical point, two emergent O(2) symmetries are revealed, and the associated conserved current operators with exact integer scaling dimensions are determined with scrutiny. Our findings provide the low-dimensional analog of DQCP where unbiased numerical results are in perfect agreement with the controlled field theoretical predictions and have extended the realm of the unconventional phase transition as well as its identification with the advanced numerical methodology.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/10722/2785992019-01-01T00:00:00Z
- Antiferromagnetism in the kagome-lattice compound α-Cu3Mg(OH)(6)Br-2http://hdl.handle.net/10722/279476Title: Antiferromagnetism in the kagome-lattice compound α-Cu3Mg(OH)(6)Br-2
Authors: Wei, Y; Feng, Z; dela Cruz, CD; Yi, W; Meng, ZY; Mei, JW; Shi, Y; Li, S
Abstract: The antiferromagnetism in α-Cu3Mg(OH)6Br2 was studied by magnetic-susceptibility, specific-heat, and neutron-diffraction measurements. The crystal structure consists of Cu2+ kagome layers with Mg2+ ions occupying the centers of the hexagons, separated by Br1-ions. The magnetic system orders antiferromagnetically at 5.4 K with the magnetic moments aligned ferromagnetically within the kagome planes. The ordered moment is 0.94μB, suggesting little quantum and geometrical fluctuations. By comparing the magnetic and specific-heat properties with those of the haydeeite, we suggest that α-Cu3Mg(OH)6Br2 may be described by the two-dimensional spin-1/2 Heisenberg kagome model and is in the region of the ferromagnetic-order side of the phase diagram. © 2019 American Physical Society.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/10722/2794762019-01-01T00:00:00Z
- Valence Bond Orders at Charge Neutrality in a Possible Two-Orbital Extended Hubbard Model for Twisted Bilayer Graphenehttp://hdl.handle.net/10722/278606Title: Valence Bond Orders at Charge Neutrality in a Possible Two-Orbital Extended Hubbard Model for Twisted Bilayer Graphene
Authors: Da Liao, Y; Meng, ZY; Xu, XY
Abstract: An extended Hubbard model on a honeycomb lattice with two orbitals per site at charge neutrality is investigated with unbiased large-scale quantum Monte Carlo simulations. The Fermi velocity of the Dirac fermions is renormalized as the cluster charge interaction increases, until a mass term emerges and a quantum phase transition from Dirac semimetal to valence bond solid (VBS) insulator is established. The quantum critical point is discovered to belong to the 3D N=4 Gross-Neveu chiral XY universality with the critical exponents obtained at high precision. Further enhancement of the interaction drives the system into two different VBS phases, the properties and transition between them are also revealed. Since the model is related to magic-angle twisted bilayer graphene, our results may have relevance towards the symmetry breaking order at the charge neutrality point of the material, and associate the wide range of universal strange metal behavior around it with quantum critical fluctuations.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/10722/2786062019-01-01T00:00:00Z
- Role of Noether’s Theorem at the Deconfined Quantum Critical Pointhttp://hdl.handle.net/10722/271431Title: Role of Noether’s Theorem at the Deconfined Quantum Critical Point
Authors: Ma, N; You, YZ; Meng, ZY
Abstract: Noether’s theorem is one of the fundamental laws of physics, relating continuous symmetries and conserved currents. Here we explore the role of Noether’s theorem at the deconfined quantum critical point (DQCP), which is a quantum phase transition beyond the Landau-Ginzburg-Wilson paradigm. It was expected that a larger continuous symmetry could emerge at the DQCP, which, if true, should lead to conserved current at low energy. By identifying the emergent current fluctuation in the spin excitation spectra, we can quantitatively study the current-current correlation in large-scale quantum Monte Carlo simulations. Our results reveal the conservation of the emergent current, as signified by the vanishing anomalous dimension of the current operator, and hence provide supporting evidence for the emergent symmetry at the DQCP. Our study demonstrates an elegant yet practical approach to detect emergent symmetry by probing the spin excitation, which could potentially guide the ongoing experimental search for the DQCP in quantum magnets.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/10722/2714312019-01-01T00:00:00Z
- Dynamics of compact quantum electrodynamics at large fermion flavorhttp://hdl.handle.net/10722/275744Title: Dynamics of compact quantum electrodynamics at large fermion flavor
Authors: Wang, W; Lu, DC; Xu, XY; You, YZ; Meng, ZY
Abstract: Thanks to the development in quantum Monte Carlo technique, the compact U(1) lattice gauge theory coupled to fermionic matter at (2+1)D is now accessible with large-scale numerical simulations, and the ground state phase diagram as a function of fermion flavor (Nf) and the strength of gauge fluctuations is mapped out. Here we focus on the large fermion flavor case (Nf=8) to investigate the dynamic properties across the deconfinement-to-confinement phase transition. In the deconfined phase, fermions coupled to the fluctuating gauge field to form U(1) spin liquid with continua in both spin and dimer spectral functions, and in the confined phase fermions are gapped out into valence bond solid phase with translational symmetry breaking and gapped spectra. The dynamical behaviors provide supporting evidence for the existence of the U(1) deconfined phase and could shine light on the nature of the U(1)-to-VBS phase transition which is of the QED3-Gross-Neveu chiral O(2) universality whose properties are still largely unknown. © 2019 American Physical Society.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/10722/2757442019-01-01T00:00:00Z
- Topological invariants for interacting topological insulators. II. Breakdown of single-particle Green's function formalismhttp://hdl.handle.net/10722/268478Title: Topological invariants for interacting topological insulators. II. Breakdown of single-particle Green's function formalism
Authors: He, Yuan Yao; Wu, Han Qing; Meng, Zi Yang; Lu, Zhong Yi
Abstract: © 2016 American Physical Society. Topological phase transitions in free fermion systems can be characterized by the closing of single-particle gap and the change in topological invariants. However, in the presence of electronic interactions, topological phase transitions can be more complicated. In paper I of this series [Phys. Rev. B 93, 195163 (2016)10.1103/PhysRevB.93.195163], we have proposed an efficient scheme to evaluate the topological invariants based on the single-particle Green's function formalism. Here, in paper II, we demonstrate several interaction-driven topological phase transitions (TPTs) in two-dimensional (2D) interacting topological insulators (TIs) via large-scale quantum Monte Carlo (QMC) simulations, based on the scheme of evaluating topological invariants presented in paper I. Across these transitions, the defining symmetries of the TIs have been neither explicitly nor spontaneously broken. In the first two models, the topological invariants calculated from the Green's function formalism succeed in characterizing the topologically distinct phases and identifying interaction-driven TPTs. However, in the other two models, we find that the single-particle gap does not close and the topological invariants constructed from the single-particle Green's function acquire no change across the TPTs. Unexpected breakdown of the Green's function formalism in constructing the topological invariants is thus discovered. We thence classify the topological phase transitions in interacting TIs into two categories in practical computation: Those that have noninteracting correspondence can be characterized successfully by the topological invariants constructed from the Green's functions, while for the others that do not have noninteracting correspondence, the Green's function formalism experiences a breakdown, but more interesting and exciting phenomena, such as emergent collective critical modes at the transition, arise. Discussion on the success and breakdown of topological invariants constructed from the Green's function formalism in the context of symmetry protected topological (SPT) states is presented.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10722/2684782016-01-01T00:00:00Z
- Visualizing a bosonic symmetry protected topological phase in an interacting fermion modelhttp://hdl.handle.net/10722/268629Title: Visualizing a bosonic symmetry protected topological phase in an interacting fermion model
Authors: Wu, Han Qing; He, Yuan Yao; You, Yi Zhuang; Yoshida, Tsuneya; Kawakami, Norio; Xu, Cenke; Meng, Zi Yang; Lu, Zhong Yi
Abstract: © 2016 American Physical Society. Symmetry protected topological (SPT) phases in free fermion and interacting bosonic systems have been classified, but the physical phenomena of interacting fermionic SPT phases have not been fully explored. Here, employing large-scale quantum Monte Carlo simulation, we investigate the edge physics of a bilayer Kane-Mele-Hubbard model with zigzag ribbon geometry. Our unbiased numerical results show that the fermion edge modes are gapped out by interaction, while the bosonic edge modes remain gapless at the (1+1)d boundary, before the bulk quantum phase transition to a topologically trivial phase. Therefore, finite fermion gaps both in the bulk and on the edge, together with the robust gapless bosonic edge modes, prove that our system becomes an emergent bosonic SPT phase at low energy, which is directly observed in an interacting fermion lattice model.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10722/2686292016-01-01T00:00:00Z
- Effect of Nematic Order on the Low-Energy Spin Fluctuations in Detwinned BaFe1.935Ni0.065As2http://hdl.handle.net/10722/268630Title: Effect of Nematic Order on the Low-Energy Spin Fluctuations in Detwinned BaFe1.935Ni0.065As2
Authors: Zhang, Wenliang; Park, J. T.; Lu, Xingye; Wei, Yuan; Ma, Xiaoyan; Hao, Lijie; Dai, Pengcheng; Meng, Zi Yang; Yang, Yi Feng; Luo, Huiqian; Li, Shiliang
Abstract: © 2016 American Physical Society. The origin of nematic order remains one of the major debates in iron-based superconductors. In theories based on spin nematicity, one major prediction is that the spin-spin correlation length at (0,π) should decrease with decreasing temperature below the structural transition temperature Ts. Here, we report inelastic neutron scattering studies on the low-energy spin fluctuations in BaFe1.935Ni0.065As2 under uniaxial pressure. Both intensity and spin-spin correlation start to show anisotropic behavior at high temperature, while the reduction of the spin-spin correlation length at (0,π) happens just below Ts, suggesting the strong effect of nematic order on low-energy spin fluctuations. Our results favor the idea that treats the spin degree of freedom as the driving force of the electronic nematic order.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10722/2686302016-01-01T00:00:00Z
- Self-learning Monte Carlo methodhttp://hdl.handle.net/10722/268479Title: Self-learning Monte Carlo method
Authors: Liu, Junwei; Qi, Yang; Meng, Zi Yang; Fu, Liang
Abstract: © 2017 American Physical Society. Monte Carlo simulation is an unbiased numerical tool for studying classical and quantum many-body systems. One of its bottlenecks is the lack of a general and efficient update algorithm for large size systems close to the phase transition, for which local updates perform badly. In this Rapid Communication, we propose a general-purpose Monte Carlo method, dubbed self-learning Monte Carlo (SLMC), in which an efficient update algorithm is first learned from the training data generated in trial simulations and then used to speed up the actual simulation. We demonstrate the efficiency of SLMC in a spin model at the phase transition point, achieving a 10-20 times speedup.
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/10722/2684792017-01-01T00:00:00Z
- Topological phase transitions with SO(4) symmetry in (2+1)D interacting Dirac fermionshttp://hdl.handle.net/10722/268587Title: Topological phase transitions with SO(4) symmetry in (2+1)D interacting Dirac fermions
Authors: Xu, Xiao Yan; Beach, K. S.D.; Sun, Kai; Assaad, F. F.; Meng, Zi Yang
Abstract: © 2017 American Physical Society. Interaction-driven topological phase transitions in Dirac semimetals are investigated by means of large-scale quantum Monte Carlo simulations. The interaction among Dirac fermions is introduced by coupling them to Ising spins that realize the quantum dynamics of the two-dimensional transverse field Ising model. The ground-state phase diagram, in which the tuning parameters are the transverse field and the coupling between fermion and Ising spins, is determined. At weak and intermediate coupling, a second-order Ising quantum phase transition and a first-order topological phase transition between two topologically distinct Dirac semimetals are observed. Interestingly, at the latter, the Dirac points smear out to form nodal lines in the Brillouin zone, and collective bosonic fluctuations with SO(4) symmetry are strongly enhanced. At strong coupling, these two phase boundaries merge into a first-order transition.
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/10722/2685872017-01-01T00:00:00Z
- Self-learning Monte Carlo method and cumulative update in fermion systemshttp://hdl.handle.net/10722/268595Title: Self-learning Monte Carlo method and cumulative update in fermion systems
Authors: Liu, Junwei; Shen, Huitao; Qi, Yang; Meng, Zi Yang; Fu, Liang
Abstract: © 2017 American Physical Society. We develop the self-learning Monte Carlo (SLMC) method, a general-purpose numerical method recently introduced to simulate many-body systems, for studying interacting fermion systems. Our method uses a highly efficient update algorithm, which we design and dub "cumulative update", to generate new candidate configurations in the Markov chain based on a self-learned bosonic effective model. From a general analysis and a numerical study of the double exchange model as an example, we find that the SLMC with cumulative update drastically reduces the computational cost of the simulation, while remaining statistically exact. Remarkably, its computational complexity is far less than the conventional algorithm with local updates.
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/10722/2685952017-01-01T00:00:00Z
- Duality between the deconfined quantum-critical point and the bosonic topological transitionhttp://hdl.handle.net/10722/268596Title: Duality between the deconfined quantum-critical point and the bosonic topological transition
Authors: Qin, Yan Qi; He, Yuan Yao; You, Yi Zhuang; Lu, Zhong Yi; Sen, Arnab; Sandvik, Anders W.; Xu, Cenke; Meng, Zi Yang
Abstract: Recently, significant progress has been made in (2 þ 1)-dimensional conformal field theories without supersymmetry. In particular, it was realized that different Lagrangians may be related by hidden dualities; i.e., seemingly different field theories may actually be identical in the infrared limit. Among all the proposed dualities, one has attracted particular interest in the field of strongly correlated quantum-matter systems: the one relating the easy-plane noncompact CP1 model (NCCP1) and noncompact quantum electrodynamics (QED) with two flavors (N ¼ 2) of massless two-component Dirac fermions. The easy-plane NCCP1 model is the field theory of the putative deconfined quantum-critical point separating a planar (XY) antiferromagnet and a dimerized (valence-bond solid) ground state, while N ¼ 2 noncompact QED is the theory for the transition between a bosonic symmetry-protected topological phase and a trivial Mott insulator. In this work, we present strong numerical support for the proposed duality. We realize the N ¼ 2 noncompact QED at a critical point of an interacting fermion model on the bilayer honeycomb lattice and study it using determinant quantum Monte Carlo (QMC) simulations. Using stochastic series expansion QMC simulations, we study a planar version of the S ¼ 1=2 J-Q spin Hamiltonian (a quantum XY model with additional multispin couplings) and show that it hosts a continuous transition between the XY magnet and the valence-bond solid. The duality between the two systems, following from a mapping of their phase diagrams extending from their respective critical points, is supported by the good agreement between the critical exponents according to the proposed duality relationships. In the J-Q model, we find both continuous and first-order transitions, depending on the degree of planar anisotropy, with deconfined quantum criticality surviving only up to moderate strengths of the anisotropy. This explains previous claims of no deconfined quantum criticality in planar two-component spin models, which were in the strong-anisotropy regime, and opens doors to further investigations of the global phase diagram of systems hosting deconfined quantum-critical points.
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/10722/2685962017-01-01T00:00:00Z
- Unified Phase Diagram for Iron-Based Superconductorshttp://hdl.handle.net/10722/268657Title: Unified Phase Diagram for Iron-Based Superconductors
Authors: Gu, Yanhong; Liu, Zhaoyu; Xie, Tao; Zhang, Wenliang; Gong, Dongliang; Hu, Ding; Ma, Xiaoyan; Li, Chunhong; Zhao, Lingxiao; Lin, Lifang; Xu, Zhuang; Tan, Guotai; Chen, Genfu; Meng, Zi Yang; Yang, Yi Feng; Luo, Huiqian; Li, Shiliang
Abstract: © 2017 American Physical Society. High-temperature superconductivity is closely adjacent to a long-range antiferromagnet, which is called a parent compound. In cuprates, all parent compounds are alike and carrier doping leads to superconductivity, so a unified phase diagram can be drawn. However, the properties of parent compounds for iron-based superconductors show significant diversity and both carrier and isovalent dopings can cause superconductivity, which casts doubt on the idea that there exists a unified phase diagram for them. Here we show that the ordered moments in a variety of iron pnictides are inversely proportional to the effective Curie constants of their nematic susceptibility. This unexpected scaling behavior suggests that the magnetic ground states of iron pnictides can be achieved by tuning the strength of nematic fluctuations. Therefore, a unified phase diagram can be established where superconductivity emerges from a hypothetical parent compound with a large ordered moment but weak nematic fluctuations, which suggests that iron-based superconductors are strongly correlated electron systems.
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/10722/2686572017-01-01T00:00:00Z
- Nearly deconfined spinon excitations in the square-lattice spin-1=2 Heisenberg antiferromagnethttp://hdl.handle.net/10722/268481Title: Nearly deconfined spinon excitations in the square-lattice spin-1=2 Heisenberg antiferromagnet
Authors: Shao, Hui; Qin, Yan Qi; Capponi, Sylvain; Chesi, Stefano; Meng, Zi Yang; Sandvik, Anders W.
Abstract: We study the spin-excitation spectrum (dynamic structure factor) of the spin-1=2 square-lattice Heisenberg antiferromagnet and an extended model (the J-Q model) including four-spin interactions Q in addition to the Heisenberg exchange J. Using an improved method for stochastic analytic continuation of imaginary-time correlation functions computed with quantum Monte Carlo simulations, we can treat the sharp (δ-function) contribution to the structure factor expected from spin-wave (magnon) excitations, in addition to resolving a continuum above the magnon energy. Spectra for the Heisenberg model are in excellent agreement with recent neutron-scattering experiments on CuðDCOOÞ2 · 4D2O, where a broad spectral-weight continuum at wave vector q ¼ ðπ; 0Þ was interpreted as deconfined spinons, i.e., fractional excitations carrying half of the spin of a magnon. Our results at ðπ; 0Þ show a similar reduction of the magnon weight and a large continuum, while the continuum is much smaller at q ¼ ðπ=2; π=2Þ (as also seen experimentally). We further investigate the reasons for the small magnon weight at ðπ; 0Þ and the nature of the corresponding excitation by studying the evolution of the spectral functions in the J-Q model. Upon turning on the Q interaction, we observe a rapid reduction of the magnon weight to zero, well before the system undergoes a deconfined quantum phase transition into a nonmagnetic spontaneously dimerized state. Based on these results, we reinterpret the picture of deconfined spinons at ðπ; 0Þ in the experiments as nearly deconfined spinons—a precursor to deconfined quantum criticality. To further elucidate the picture of a fragile ðπ; 0Þ-magnon pole in the Heisenberg model and its depletion in the J-Q model, we introduce an effective model of the excitations in which a magnon can split into two spinons that do not separate but fluctuate in and out of the magnon space (in analogy to the resonance between a photon and a particle-hole pair in the exciton-polariton problem). The model can reproduce the reduction of magnon weight and lowered excitation energy at ðπ; 0Þ in the Heisenberg model, as well as the energy maximum and smaller continuum at ðπ=2; π=2Þ. It can also account for the rapid loss of the ðπ; 0Þ magnon with increasing Q and the remarkable persistence of a large magnon pole at q ¼ ðπ=2; π=2Þ even at the deconfined critical point. The fragility of the magnons close to ðπ; 0Þ in the Heisenberg model suggests that various interactions that likely are important in many materials—e.g., longer-range pair exchange, ring exchange, and spin-phonon interactions—may also destroy these magnons and lead to even stronger spinon signatures than in CuðDCOOÞ2 · 4D2O.
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/10722/2684812017-01-01T00:00:00Z
- Evolution of the superconductivity dome in the two-dimensional Hubbard modelhttp://hdl.handle.net/10722/268655Title: Evolution of the superconductivity dome in the two-dimensional Hubbard model
Authors: Chen, K. S.; Meng, Z. Y.; Yang, S. X.; Pruschke, T.; Moreno, J.; Jarrell, M.
Abstract: In a recent publication, we identified a line of Lifshitz transition points separating the Fermi liquid and pseudogap regions in the hole-doped two-dimensional Hubbard model. Here, we extend the study to further determine the superconducting transition temperature in the phase diagram. By means of large-scale dynamical cluster quantum Monte Carlo simulations, we are able to identify the evolution of the d-wave superconducting dome in the hole-dope side of the phase diagram, with next-nearest-neighbor hopping (t′), chemical potential, and temperature as control parameters. To obtain the superconducting transition temperature Tc, we employ two-particle measurements of the pairing susceptibilities. As t′goes from positive to negative values, we find the d-wave projected irreducible pairing vertex function is enhanced, and the curvature of its doping dependence changes from convex to concave, which fixes the position of the maximum superconducting temperature at the same filling (n≈0.85) and constraints the dome from precisely following the Lifshitz line. We furthermore decompose the irreducible vertex function into fully irreducible, charge and spin components via the parquet equations, and consistently find that the spin component dominates the pairing vertex function in the doping range where the dome is located. Our investigations deepen the understanding of the phase diagram of the two-dimensional Hubbard model and, more importantly, pose new questions to the field. For example, we found as t′goes from positive to negative values, the curvature of the pairing strength as a function of doping changes from convex to concave, and the nature of the dominant fluctuations changes from charge degree of freedom to spin degree of freedom. The study of these issues will lead to further understanding of the phase diagram of the two-dimensional Hubbard model and also the physics of the hole-doped cuprate high-temperature superconductors. © 2013 American Physical Society.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10722/2686552013-01-01T00:00:00Z
- Dual-fermion approach to interacting disordered fermion systemshttp://hdl.handle.net/10722/268616Title: Dual-fermion approach to interacting disordered fermion systems
Authors: Yang, S. X.; Haase, P.; Terletska, H.; Meng, Z. Y.; Pruschke, T.; Moreno, J.; Jarrell, M.
Abstract: We generalize the recently introduced dual-fermion (DF) formalism for disordered fermion systems by including the effect of interactions. For an interacting disordered system the contributions to the full vertex function have to be separated into crossing-asymmetric and crossing-symmetric scattering processes, and addressed differently when constructing the DF diagrams. By applying our approach to the Anderson-Falicov-Kimball model and systematically restoring the nonlocal correlations in the DF lattice calculation, we show a significant improvement over the dynamical mean-field theory and the coherent potential approximation for both one-particle and two-particle quantities. © 2014 American Physical Society.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10722/2686162014-01-01T00:00:00Z
- Effective cluster typical medium theory for the diagonal Anderson disorder model in one- and two-dimensionshttp://hdl.handle.net/10722/268558Title: Effective cluster typical medium theory for the diagonal Anderson disorder model in one- and two-dimensions
Authors: Ekuma, Chinedu E.; Terletska, Hanna; Meng, Zi Yang; Moreno, Juana; Jarrell, Mark; Mahmoudian, Samiyeh; Dobrosavljević, Vladimir
Abstract: We develop a cluster typical medium theory to study localization in disordered electronic systems. Our formalism is able to incorporate non-local correlations beyond the local typical medium theory in a systematic way. The cluster typical medium theory utilizes the momentum-resolved typical density of states and hybridization function to characterize the localization transition. We apply the formalism to the Anderson model of localization in one- and two-dimensions. In one-dimension, we find that the critical disorder strength scales inversely with the linear cluster size with a power law, Wc ∼ (1/Lc) 1/ν , whereas in two-dimensions, the critical disorder strength decreases logarithmically with the linear cluster size. Our results are consistent with previous numerical work and are in agreement with the one-parameter scaling theory. © 2014 IOP Publishing Ltd.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10722/2685582014-01-01T00:00:00Z
- Theoretical prediction of fragile Mott insulators on plaquette Hubbard latticeshttp://hdl.handle.net/10722/268566Title: Theoretical prediction of fragile Mott insulators on plaquette Hubbard lattices
Authors: Wu, Han Qing; He, Rong Qiang; Meng, Zi Yang; Lu, Zhong Yi
Abstract: © 2015 American Physical Society. Employing extensive cellular dynamical mean-field theory calculations with an exact diagonalization impurity solver, we investigate the ground-state phase diagrams and nonmagnetic metal-insulator transitions of the half-filled Hubbard model on two plaquette (the 1/5 depleted and checkerboard) square lattices. We identify three different insulators in the phase diagrams: dimer insulator, antiferromagnetic insulator, and plaquette insulator. We also demonstrate that the plaquette insulator is a novel fragile Mott insulator (FMI) which features a nontrivial one-dimensional irreducible representation of the C4v crystalline point group and cannot be adiabatically connected to any band insulator with time-reversal symmetry. Furthermore, we study the nonmagnetic quantum phase transitions from the metal to the FMI and find that this Mott metal-insulator transition is characterized by the splitting of the noninteracting bands due to interaction effects.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10722/2685662015-01-01T00:00:00Z
- Mott transition in the triangular lattice Hubbard model: A dynamical cluster approximation studyhttp://hdl.handle.net/10722/268568Title: Mott transition in the triangular lattice Hubbard model: A dynamical cluster approximation study
Authors: Dang, Hung T.; Xu, Xiao Yan; Chen, Kuang Shing; Meng, Zi Yang; Wessel, Stefan
Abstract: © 2015 American Physical Society. Based on dynamical cluster approximation (DCA) quantum Monte Carlo simulations, we study the interaction-driven Mott metal-insulator transition (MIT) in the half-filled Hubbard model on the anisotropic two-dimensional triangular lattice, where the degree of frustration is varied between the unfrustrated case and the fully frustrated, isotropic triangular lattice. Upon increasing the DCA cluster size, we analyze the evolution of the MIT phase boundary as a function of frustration in the phase diagram spanned by the interaction strength and temperature, and provide a quantitative description of the MIT phase boundary in the triangular lattice Hubbard model. Qualitative differences in the phase boundary between the unfrustrated and fully frustrated cases are exhibited. In particular, a change in the sign of the phase boundary slope is observed, which via an impurity cluster eigenstate analysis, may be related to a change in the nature of the insulating state. We discuss our findings within the scenario that the triangular lattice electron system might exhibit a quantum critical Mott MIT with a possible quantum spin liquid insulating state, such as considered for the organic charge transfer salts κ-(BEDT-TTF)2Cu2(CN)3 and EtMe3Sb[Pd(dmit)2]2.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10722/2685682015-01-01T00:00:00Z
- Evidence for spin-triplet odd-parity superconductivity close to type-II van Hove singularitieshttp://hdl.handle.net/10722/268569Title: Evidence for spin-triplet odd-parity superconductivity close to type-II van Hove singularities
Authors: Meng, Zi Yang; Yang, Fan; Chen, Kuang Shing; Yao, Hong; Kee, Hae Young
Abstract: © 2015 American Physical Society. Searching for unconventional Cooper pairing states has been at the heart of superconductivity research since the discovery of BCS superconductors. In particular, spin-triplet odd-parity pairing states were recently revisited due to the possibility of tuning towards topological superconductors. In this context, it is interesting to note a recent proposal that such a spin-triplet pairing instability occurs when the band filling is near van Hove singularities (vHS) associated with momenta away from time-reversal invariant momenta named type-II vHS. However, this result was obtained within a weak coupling renormalization group with Fermi surface patch approximation. To explore superconducting instabilities beyond this weak coupling Fermi surface patch approximation, we perform systematic study on the Hubbard model in a two-dimensional square lattice using three different methods: random phase approximation, large-scale dynamical mean-field theory simulations with continuous time quantum Monte Carlo (CTQMC) impurity solver, and large-scale dynamical cluster simulations with the CTQMC cluster solver. We find, in a wide doping range centered around the type-II van Hove filling, a twofold degenerate, spin-triplet, odd-parity p-wave pairing state emerges due to repulsive interaction, when the Fermi surface is not sufficiently nested. Possible relevance of our findings to the recently discovered superconductors LaO1-xFxBiS2,Ir1-xPtxTe2, and proposed doped BC3 are also discussed.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10722/2685692015-01-01T00:00:00Z
- Bona fide interaction-driven topological phase transition in correlated symmetry-protected topological stateshttp://hdl.handle.net/10722/268575Title: Bona fide interaction-driven topological phase transition in correlated symmetry-protected topological states
Authors: He, Yuan Yao; Wu, Han Qing; You, Yi Zhuang; Xu, Cenke; Meng, Zi Yang; Lu, Zhong Yi
Abstract: © 2016 American Physical Society. It is expected that the interplay between nontrivial band topology and strong electron correlation will lead to very rich physics. Thus a controlled study of the competition between topology and correlation is of great interest. Here, employing large-scale quantum Monte Carlo simulations, we provide a concrete example of the Kane-Mele-Hubbard model on an AA-stacking bilayer honeycomb lattice with interlayer antiferromagnetic interaction. Our simulation identified several different phases: a quantum spin Hall insulator (QSH), an xy-plane antiferromagnetic Mott insulator, and an interlayer dimer-singlet insulator. Most importantly, a bona fide topological phase transition between the QSH and the dimer-singlet insulators, purely driven by the interlayer antiferromagnetic interaction, is found. At the transition, the spin and charge gap of the system close while the single-particle excitations remain gapped, which means that this transition has no mean-field analog and it can be viewed as a transition between bosonic symmetry-protected topological (SPT) states. At one special point, this transition is described by a (2+1)dO(4) nonlinear sigma model with exact SO(4) symmetry and a topological term at exactly Θ=π. The relevance of this work towards more general interacting SPT states is discussed.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10722/2685752016-01-01T00:00:00Z
- Topological invariants for interacting topological insulators. I. Efficient numerical evaluation scheme and implementationshttp://hdl.handle.net/10722/268477Title: Topological invariants for interacting topological insulators. I. Efficient numerical evaluation scheme and implementations
Authors: He, Yuan Yao; Wu, Han Qing; Meng, Zi Yang; Lu, Zhong Yi
Abstract: © 2016 American Physical Society. The aim of this series of two papers is to discuss topological invariants for interacting topological insulators (TIs). In the first paper (I), we provide a paradigm of efficient numerical evaluation scheme for topological invariants, in which we demystify the procedures and techniques employed in calculating Z2 invariant and spin Chern number via zero-frequency single-particle Green's function in quantum Monte Carlo (QMC) simulations. Here we introduce an interpolation process to overcome the ubiquitous finite-size effect, so that the calculated spin Chern number shows ideally quantized values. We also show that making use of symmetry properties of the underlying systems can greatly reduce the computational effort. To demonstrate the effectiveness of our numerical evaluation scheme, especially the interpolation process, for calculating topological invariants, we apply it on two independent two-dimensional models of interacting topological insulators. In the subsequent paper (II), we apply the scheme developed here to wider classes of models of interacting topological insulators, for which certain limitation of constructing topological invariant via single-particle Green's functions will be presented.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10722/2684772016-01-01T00:00:00Z
- Charge-Density-Wave Transitions of Dirac Fermions Coupled to Phononshttp://hdl.handle.net/10722/268611Title: Charge-Density-Wave Transitions of Dirac Fermions Coupled to Phonons
Authors: Chen, Chuang; Xu, Xiao Yan; Meng, Zi Yang; Hohenadler, Martin
Abstract: © 2019 American Physical Society. The spontaneous generation of charge-density-wave order in a Dirac fermion system via the natural mechanism of electron-phonon coupling is studied in the framework of the Holstein model on the honeycomb lattice. Using two independent and unbiased quantum Monte Carlo methods, the phase diagram as a function of temperature and coupling strength is determined. It features a quantum critical point as well as a line of thermal critical points. Finite-size scaling appears consistent with fermionic Gross-Neveu-Ising universality for the quantum phase transition and bosonic Ising universality for the thermal phase transition. The critical temperature has a maximum at intermediate couplings. Our findings motivate experimental efforts to identify or engineer Dirac systems with sufficiently strong and tunable electron-phonon coupling.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/10722/2686112019-01-01T00:00:00Z
- Quantum Spin Liquid with even Ising Gauge Field Structure on Kagome Latticehttp://hdl.handle.net/10722/268603Title: Quantum Spin Liquid with even Ising Gauge Field Structure on Kagome Lattice
Authors: Wang, Yan Cheng; Zhang, Xue Feng; Pollmann, Frank; Cheng, Meng; Meng, Zi Yang
Abstract: © 2018 American Physical Society. Employing large-scale quantum Monte Carlo simulations, we study the extended XXZ model on the kagome lattice. A Z2 quantum spin liquid phase with effective even Ising gauge field structure emerges from the delicate balance among three symmetry-breaking phases including stripe solid, staggered solid, and ferromagnet. This Z2 spin liquid is stabilized by an extended interaction related to the Rokhsar-Kivelson potential in the quantum dimer model limit. The phase transitions from the staggered solid to a spin liquid or ferromagnet are found to be first order and so is the transition between the stripe solid and ferromagnet. However, the transition between a spin liquid and ferromagnet is found to be continuous and belongs to the 3D XY∗ universality class associated with the condensation of spinons. The transition between a spin liquid and stripe solid appears to be continuous and associated with the condensation of visons.
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/10722/2686032018-01-01T00:00:00Z
- Dynamical Signature of Symmetry Fractionalization in Frustrated Magnetshttp://hdl.handle.net/10722/268605Title: Dynamical Signature of Symmetry Fractionalization in Frustrated Magnets
Authors: Sun, Guang Yu; Wang, Yan Cheng; Fang, Chen; Qi, Yang; Cheng, Meng; Meng, Zi Yang
Abstract: © 2018 American Physical Society. The nontriviality of quantum spin liquids (QSLs) typically manifests in the nonlocal observables that signify their existence; however, this fact actually casts a shadow on detecting QSLs with experimentally accessible probes. Here, we provide a solution by unbiasedly demonstrating a dynamical signature of anyonic excitations and symmetry fractionalization in QSLs. Employing large-scale quantum Monte Carlo simulation and stochastic analytic continuation, we investigate the extended XXZ model on the kagome lattice, and find out that, across the phase transitions from Z2 QSLs to different symmetry breaking phases, spin spectral functions can reveal the presence and condensation of emergent anyonic spinon and vison excitations, in particular, the translational symmetry fractionalization of the latter, which can be served as the dynamical signature of the seemingly ephemeral QSLs in spectroscopic techniques such as inelastic neutron or resonance (inelastic) x-ray scatterings.
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/10722/2686052018-01-01T00:00:00Z
- Dynamical signature of fractionalization at a deconfined quantum critical pointhttp://hdl.handle.net/10722/268609Title: Dynamical signature of fractionalization at a deconfined quantum critical point
Authors: Ma, Nvsen; Sun, Guang Yu; You, Yi Zhuang; Xu, Cenke; Vishwanath, Ashvin; Sandvik, Anders W.; Meng, Zi Yang
Abstract: © 2018 American Physical Society. Deconfined quantum critical points govern continuous quantum phase transitions at which fractionalized (deconfined) degrees of freedom emerge. Here we study dynamical signatures of the fractionalized excitations in a quantum magnet (the easy-plane J-Q model) that realize a deconfined quantum critical point with emergent O(4) symmetry. By means of large-scale quantum Monte Carlo simulations and stochastic analytic continuation of imaginary-time correlation functions, we obtain the dynamic spin-structure factors in the Sx and Sz channels. In both channels, we observe broad continua that originate from the deconfined excitations. We further identify several distinct spectral features of the deconfined quantum critical point, including the lower edge of the continuum and its form factor on moving through the Brillouin zone. We provide field-theoretical and lattice model calculations that explain the overall shapes of the computed spectra, which highlight the importance of interactions and gauge fluctuations to explain the spectral-weight distribution. We make further comparisons with the conventional Landau O(2) transition in a different quantum magnet, at which no signatures of fractionalization are observed. The distinctive spectral signatures of the deconfined quantum critical point suggest the feasibility of its experimental detection in neutron scattering and nuclear magnetic resonance experiments.
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/10722/2686092018-01-01T00:00:00Z