Novel Quantum States with Exotic Spin Properties - Unconventional Generalization of Magnetism.

摘要

My group has investigated the unconventional meta-magnetic states in the Sr3Ru2O7 system, topological insulators, and superconductivity in iron- based superconductors. First, we constructed the microscopic mechanism of the nematic states in the Sr3Ru2O7 system based on its quasi-one-dimensional band structure. The calculated phase diagram agrees with the experimental observation. We performed the detailed theoretical analysis of the quasi- particle interference (QPI) spectroscopy of the STM measurement, which is in nice agreement with the experimental results. Second, we studied strong correlation effects in the 2D topological insulators by performing the sign- problem-free quantum Monte-Carlo simulations, and obtained the phase diagram. How the edge states are destabilized at an intermediate interaction strength is investigated. We have also constructed models of 3D topological insulators based on the generalization of Landau levels. The elegant analytical properties of Landau level provides a good starting point for the future study of fractional topological insulators in 3D. Third, we have investigated the unconventional superconductivity in iron-based superconductors. Time-reversal symmetry breaking states are proposed and the experimentally testable signatures are presented. We further provided a theory explanation of the anisotropic states observed in FeSe superconductors based on orbital ordering.