Interaction-induced quantum spin Hall insulator in the organic Dirac electron system $\alpha$-(BEDT-TSeF)${}_2$I${}_3$

Abstract

Focusing on the recently-discovered candidate topological insulator $\alpha$-(BEDT-TSeF)${}_2$I${}_3$ -- having two-dimensional charge-neutral Dirac cones in a low symmetry lattice -- we combine ab-initio and extended-Hubbard model calculations to deal with spin-orbit and non-local repulsive interactions, and find a realization of an interaction-induced quantum spin Hall (QSH) insulator, similar to the one proposed in the honeycomb lattice under next-nearest neighbor repulsions. In the absence of repulsive interactions, a topological insulator appears by the spin-orbit coupling and is characterized by a nonzero spin Chern number. By considering up to next-nearest neighbor repulsions at Hartree-Fock level, the intrinsic spin-orbit gap is found to grow by orders of magnitude and a QSH insulating phase appears that has both a finite spin Chern number and order parameter. Transport coefficients and spin susceptibility are calculated and found to consistently account for most of the experimental findings, including the metal-to-insulator crossover occurring at $\sim 50$ K as well as the Berry phase change from 0 to $\pi$ under hydrostatic pressure. We argue that such a QSH insulating phase does not necessitate a sizeable spin-orbit interaction to generate a large insulating gap, which is highly advantageous for the search of novel topological phases in generic materials having low symmetry lattice and/or small spin-orbit coupling.

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Cited by in corpus (9)

• Comprehensive $ab$ $initio$ investigation of the phase diagram of quasi-one-dimensional molecular solids
• Gap opening mechanism for correlated Dirac electrons in organic compounds $\alpha$-(BEDT-TTF)${}_2$I${}_3$ and $\alpha$-(BEDT-TSeF)${}_2$I${}_3$
• Correlation-driven organic 3D topological insulator with relativistic fermions
• H-wave -- A Python package for the Hartree-Fock approximation and the random phase approximation
• Correlated Zak insulator in organic antiferromagnets
• Three-Dimensional Topological Semimetal/Insulator States in α-Type Organic Conductors with Interlayer Spin-Orbit Interaction
• Observations of $\nu =1$ Quantum Hall Effect and Inter-Band Effects of Magnetic fields on Hall Conductivity in Organic Massless Dirac Fermion System $\alpha$-(BETS)${}_2$I${}_3$ under Pressure
• Spin-Orbit Coupling Effect on the Seebeck Coefficient in Dirac Electron Systems in $\alpha$-(BETS)${}_2$I${}_3$
• Ambient-Pressure Organic Dirac Electron State in $\alpha$-(BETS)${}_2$AuCl${}_2$