Theoretical Nanophysics

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Four-spin terms and the origin of the chiral spin liquid in Mott insulators on the triangular lattice

Johannes Motruk, University of Geneva

17.09.2021 at 09:00 



At strong repulsion, the triangular-lattice Hubbard model is described by S=1/2 spins with nearest-neighbor antiferromagnetic Heisenberg interactions and exhibits conventional 120° order. When decreasing the interaction, additional four-spin interactions are naturally generated from the underlying Mott-insulator physics of electrons. Although these interactions have historically been connected with a gapless ground state with emergent spinon Fermi surface (SFS), we find that at physically relevant parameters, they stabilize a chiral spin-liquid (CSL) of Kalmeyer-Laughlin (KL) type, clarifying observations in recent studies of the Hubbard model. We then present a self-consistent solution based on a mean-field rewriting of the interaction to obtain a Hamiltonian with similarities to the parent Hamiltonian of the KL state, providing a physical understanding for the origin of the CSL. Using a combination of the infinite density matrix renormalization group and exact diagonalization, we also study the wider phase diagram of the spin model, shedding light on the fate of the SFS state. Finally, we will comment on experimental systems where triangular lattice Hubbard model physics might be observed.