Formation of energy gap in high-dimensional spin-orbital liquids

Abstract

A Schwinger boson mean-field theory is developed for spin liquids in a symmetric spin-orbital model in higher dimensions. Spin, orbital and coupled spin-orbital operators are treated equally. We evaluate the dynamic correlation functions and collective excitations spectra. As the collective excitations have a finite energy gap, we conclude that the ground state is a spin-orbital liquid with a two-fold degeneracy, which breaks the discrete spin-orbital symmetry. Based on this conclusion, we propose that broken symmetry or symmetric frustration instead of geometric quantum frustration provides a new route to explore the spin liquid states. Possible relevence of this spin liquid state to several realistic systems, such as CaV 4O 9 and Na 2Sb 2Ti 2O, are discussed.