Spontaneous Parity Breaking in Spin-Orbital Coupled Systems

TL;DR

This paper investigates how spontaneous parity breaking occurs in a two-band Hubbard model on a honeycomb lattice, revealing novel spin-orbital orders, magnetoelectric effects, and topological phases driven by electron correlations.

Contribution

It introduces a minimal model demonstrating spontaneous parity breaking with detailed symmetry and mean-field analyses, uncovering new ordered states and their properties.

Findings

Identification of spin-orbital composite and charge ordered states at 1/4 filling

Discovery of magnetoelectric responses in the composite ordered phase

Observation of spin splitting and topological variations in the band structure

Abstract

Effects of spontaneous parity breaking by charge, spin, and orbital orders are investigated in a two-band Hubbard model on a honeycomb lattice. This is a minimal model in which the inter-orbital hopping, atomic spin-orbit coupling, and strong electron correlation give rise to fascinating properties, such as the magnetoelectric effects, quantum spin Hall effect, and spin or valley splitting in the band structure. We perform the symmetry analysis of possible broken-parity states and the mean-field analysis of their competition. We find that the model at 1/4 filling exhibits a spin-orbital composite ordered state and a charge ordered state, in addition to a paramagnetic quantum spin-Hall insulator. We show that the composite ordered phase exhibits two types of magnetoelectric responses. The charge ordered state shows spin splitting in the band structure, while the topological nature varies depending on electron correlations.