DSpace Collection:http://hdl.handle.net/10722/386332024-03-29T16:00:11Z2024-03-29T16:00:11ZProperties and interplay of carrier and exciton in moiré systemXiao, Chengxin肖承鑫http://hdl.handle.net/10722/3415982024-03-18T09:56:17Z2024-01-01T00:00:00ZTitle: Properties and interplay of carrier and exciton in moiré system
Authors: Xiao, Chengxin; 肖承鑫
Abstract: The development of moiré systems based on various materials such as
magnetic topological materials, transition metal dichalcogenides (TMDs),
hexagonal boron nitride (h-BN) and graphene has generated significant
interest. These systems are considered promising platforms for investigat-
ing charge carrier properties and exciton properties in moiré potential and
the corresponding many-body correlation phenomena in a flexible manner.
This thesis explores three distinct moiré systems, namely, MnBi2Te4 with
spin texture from twisted magnetic substrate, twisted h-BN as the substrate
and twisted bilayer TMDs. We investigate various aspects in these systems,
including charge carrier properties, formation of moiré potential near the
twisted interface, and the impact of the charge carrier-exciton interaction.
Regarding MnBi2Te4 spin texture, we established that for magnetization
textures with closed domain wall geometries, the formed superlattice mini-
band is a gapped Dirac cone.
This cone features orbital magnetization
from the current circulation in the closed loops of chiral channels. In con-
trast, magnetization textures with open domain wall geometries result in
gapless mini-Dirac cones. Through our investigations of twisted h-BN, we
observed that the interface creates a universal superlattice potential and
electric field in various 2D materials placed on top of it. We then general-
ized this idea to AB-stacked h-BN subject to torsion with adjacent layers all
twisted with an angle in the same direction. This enabled scalability of the
potential and field strength with film thickness, ultimately saturating to a
quasi-periodic structure with chiral features. Lastly, in the twisted bilayer
TMDs system, we found that through the Coulomb exchange between mo-
bile interlayer excitons and charge carriers, the interlayer exciton bath could
mediate both Heisenberg and Dzyaloshinskii-Moriya type spin interactions
between moiré trapped charge carriers. These interactions were control-
lable by exciton density and exciton spin current, respectively. We showed
that the strong Heisenberg interactions and the extraordinarily long-ranged
Dzyaloshinskii-Moriya interactions could establish robust spin spiral mag-
netic orders in Mott-Wigner crystal states at various filling factors, with
the spiral direction controlled by the exciton current.2024-01-01T00:00:00ZMetal oxide and carbide nanomaterials : catalysis, photocatalysis, and oxygen adsorption applicationsHe, Yanling何颜玲http://hdl.handle.net/10722/3415252024-03-18T09:55:35Z2023-01-01T00:00:00ZTitle: Metal oxide and carbide nanomaterials : catalysis, photocatalysis, and oxygen adsorption applications
Authors: He, Yanling; 何颜玲
Abstract: Nanomaterials are anticipated to play a crucial role in the advancement of future technologies, exhibiting great potential for various applications. The field of study concerning nanomaterials is extensive, thus necessitating a focused approach on specific classes of materials and applications. In this study, we specifically investigated nanomaterials for the following applications:
1) Food packaging, as it contributes to enhanced food security;
2) Catalysis, which contributes to fuel generation through water-gas-shift reactions or catalytic hydrocracking of plastics, thereby promoting clean energy and a circular economy;
3) Photocatalysis for environmental remediation, addressing water pollution and ensuring a clean water supply.
This thesis focuses on the investigation of metal oxide and metal carbide nanomaterials, specifically mesoporous silica, photocatalytically active metal oxide semiconductors (ZnO, TiO2), and catalytically active metal carbides (MoxC, TiCx). Mesoporous silica nanomaterials possess a large surface area, adjustable porosity and pore sizes, and can be easily modified. In this study, we synthesized mesoporous silica nanoparticles (MSNs) using the Stöber method, resulting in a specific surface area exceeding 800 m2/g. Subsequently, we deposited FeOx and TiOx coatings on the surfaces of MSNs using atomic layer deposition (ALD). Additionally, we applied a layer of carbonized glucose to the MSNs using the hydrothermal method, varying the amount of glucose. Notably, the MSNs with 60 mg of glucose exhibited exceptional performance in dry air with the oxygen absorption capacity of 164.8 mL/g, which was approximately five times higher than that of the commercially iron-based oxygen scavenger.
Moreover, metal oxides such as TiO2 and ZnO have been extensively utilized for the degradation of organic pollutants, including dye and plastics. In this study, we aimed to investigate the degradation of organic dye by depositing a layer of self-doped black TiO2 onto the surfaces of P25, ZnO, and SnO2 particles, respectively. Through the adjustment of various parameters, we discovered that amorphous black titanium dioxide on P25 exhibited the highest photocatalytic performance. The photocatalytic mechanism was examined by ESR and the results indicated that the presence of oxygen vacancies and Ti3+ defects significantly contributed to the exceptional catalytic performance of black TiO2. In the degradation of microplastics, TiO2/ZnO core-shell tetrapods were employed as photocatalysts for the degradation of PE, PES, and PP plastics collected from the environment. These microplastics share common characteristics of having a highly stable structure, making them resistant to biodegradation. However, with the addition of an electron scavenger, complete degradation of these three plastics was achieved within a timeframe ranging from 400 to 816 h. Additionally, apart from photocatalytic degradation, microplastics can also be degraded through thermochemical methods, which offer the advantage of generating value-added products (such as fuels) as byproducts of the degradation process. Notably, MoCx and TiCx exhibit exceptional thermal stability, and excellent corrosion resistance, making them highly suitable for catalytic applications. In our study, we investigated the catalytic hydrocracking of plastics using metal clusters supported on different metal carbide catalysts (TiCx, MoxC). Remarkably, we observed that the Ru clusters/MoC catalyst resulted in excellent plastic degradation performance.2023-01-01T00:00:00ZQuantum filter algorithms for solving ground-state problem of local HamiltoniansHe, Minquan何敏權http://hdl.handle.net/10722/3366212024-02-26T08:30:46Z2023-01-01T00:00:00ZTitle: Quantum filter algorithms for solving ground-state problem of local Hamiltonians
Authors: He, Minquan; 何敏權
Abstract: Simulating the quantum many-body systems is an important task in many fields, such as quantum chemistry, condensed-matter physics, and high-energy physics. However, it is difficult to solve this kind of task for conventional computers, especially when the system scale is large. Quantum computation provides an efficient way to simulate the quantum system of interest, may overcoming the large-size problem. One of the key problems in this field is to solve the ground state problem of local Hamiltonian. This thesis presents two approaches for this crucial task.
The first part of this study proposes an Inverse Iteration Quantum Eigensolver, which enhances the classical inverse power iteration method with the capabilities of quantum computing. A pivotal element of this method involves the construction of an inverse Hamiltonian as a linear combination of coherent Hamiltonian evolution. This task is achieved using a continuous-variable quantum mode, which enables the encoding of a linear combination as an integral into a quantum mode resource state. The algorithm’s effectiveness is demonstrated through numerical simulations for a range of physical systems, including molecules and quantum many-body models. A hybrid quantum-classical algorithm, leveraging continuous-variable resources for reducing coherent evolution time of Hamiltonians, is also introduced and compared with the purely quantum approach.
The latter part of the thesis introduces the Quantum Gaussian Filter (QGF), an algorithm that efficiently projects a superposed quantum state onto a target state, provided sufficient overlap exists between the two states. The QGF algorithm employs a Gaussian function of the system Hamiltonian as the filter operator. A hybrid quantum-classical implementation is presented, feasible on near-term quantum computers, which realizes the Quantum Gaussian Filter as a linear combination of Hamiltonian evolution at various time points. Significantly, the linear combination coefficients are determined classically and can be optimized post-processing. This algorithm is demonstrated using numerical simulations for the quantum Ising model under noise. A full-quantum realization of the Quantum Gaussian Filter with an ancillary continuous- variable is also provided for comparison, emphasizing the hybrid approach’s flexibility due to post-processing capabilities on classical computers.2023-01-01T00:00:00ZJovian magnetospheric responses to internal and external processesFeng, Enhao馮恩豪http://hdl.handle.net/10722/3366182024-02-26T08:30:44Z2023-01-01T00:00:00ZTitle: Jovian magnetospheric responses to internal and external processes
Authors: Feng, Enhao; 馮恩豪
Abstract: The complexity of the Jovian magnetosphere arises from Jupiter’s rapid rotation and the Io plasma source. Thus, physical processes of the Jovian magnetosphere are very different from that in the Earth’s magnetosphere and have yet to be fully understood. However, observations, theoretical models, and numerical simulations may not accurately reflect or explain some processes of the Jovian magnetosphere to a certain extent, and may even lead to some contradictions, for example:
1. According to the corotation breakdown model, the intensity of the Jovian auroral main emission is expected to decrease during solar wind compression (SWC) period. However, multiband observations have shown overall enhancement of the auroral emission during SWC, which contradicts the theoretical model.
2. Observations have shown that the location of Jovian magnetopause can vary rapidly and greatly. The drastic variation of the Jovian magnetopause location is generally believed to be caused by external conditions, i.e., drastic changes in the solar wind ram pressure. Moreover, most previous theoretical and numerical models are relatively symmetric and static for the internal Jovian magnetospheric conditions, such as the dynamics of the Jovian magnetodisc. Therefore, previous models lack detailed explanations for the effect of internal mechanisms on the drastic variations of the Jovian magnetopause.
To investigate the important problems related to the physical processes of the Jovian magnetosphere being controlled by internal and external conditions, I conduct a series of three-dimensional global MHD simulations of the Jovian magnetosphere. Based on the results of the study, the thesis shows:
1. the simulations with SWC indicate that both upward field-aligned current and downward Alfvénic Poynting flux undergo nonlinear variations during SWC, which is consistent with change trend of the auroral UV power in observations.
2. the variation of Jovian magnetopause can be particularly dramatic, with the standoff distance near noon varying by up to 50 Jovian radii even under constant solar wind conditions. Moreover, the variation frequency of the magnetopause is very high, about once per 1 – 2 hours.
3. the mass loading rate of the Io plasma torus has a very important impact on the Jovian magnetodisc and even the entire Jovian magnetosphere. Specifically, the formation and transportation of the interchange structures and the evolution of the magnetodisc are greatly influenced by the mass loading rate.
In summary, the study on the responses of the Jovian magnetosphere suggests that different Jovian auroral activities including brightening or dimming can be observed during SWC period, and the study provides new insights into future research themes on the interaction between the Jovian magnetosphere and the external environment. In addition, the study on the Jovian magnetosphere responses to internal conditions provides important new context for interpreting the Jovian magnetopause location and dynamics, with key implications for other internally mass-loaded and/or rapidly rotating systems.2023-01-01T00:00:00Z