Spin and orbital valence bond solids in a one-dimensional spin-orbital system: Schwinger boson mean-field theory

Abstract

A generalized one-dimensional SU (2) ×SU (2) spin-orbital model is studied by means of Schwinger boson mean-field theory (SBMFT). We focus on exploring the dimer phases and clarify how to capture properly the low-temperature properties of the system. The phase diagrams for the cases of S=T=1/2 and of S=1 and T=1/2 are presented. Three dimer phases, the orbital valence bond state, spin valence bond state and spin-orbital valence bond state, are found to arise in proper parameter regions. The results indicate that the SU (2) ×SU (2) type of spin-orbit coupling can serve as both the spin-Peierls and orbital-Peierls mechanisms which are responsible for the formations of spin singlet and orbital singlet, respectively. We have also calculated the static spin and pseudospin susceptibilities in the SBMFT scheme to characterize and distinguish the three types of dimer phases. © 2005 The American Physical Society.