Emergent spin-valley-orbital physics by spontaneous parity breaking

TL;DR

This paper explores how electron correlations can induce spontaneous inversion symmetry breaking in centrosymmetric lattices, leading to emergent spin-valley-orbital phenomena and novel electronic properties without inherent lattice asymmetry.

Contribution

It provides a theoretical framework for understanding how spontaneous electronic ordering can generate antisymmetric spin-orbit coupling in symmetric lattices, revealing new spin-valley-orbital physics.

Findings

Identification of antisymmetric spin-orbit coupling in various orders

Complete classification of order-induced spin-valley-orbital effects

Insights into magnetic, elastic, and optical responses in correlated systems

Abstract

The spin-orbit coupling in the absence of spatial inversion symmetry plays an important role in realizing intriguing electronic states in solids, such as topological insulators and unconventional superconductivity. Usually, the inversion symmetry breaking is inherent in the lattice structures, and hence, it is not easy to control these interesting properties by external parameters. We here theoretically investigate the possibility of generating the spin-orbital entanglement by spontaneous electronic ordering caused by electron correlations. In particular, we focus on the centrosymmetric lattices with local asymmetry at the lattice sites, e.g., zig-zag, honeycomb, and diamond structures. In such systems, conventional staggered orders, such as charge order and antiferromagnetic order, break the inversion symmetry and activate the antisymmetric spin-orbit coupling, which is hidden in a sublattice-dependent form in the paramagnetic state. Considering a minimal two-orbital model on a honeycomb lattice, we scrutinize the explicit form of the antisymmetric spin-orbit coupling for all the possible staggered charge, spin, orbital, and spin-orbital orders. We show that the complete table is useful for understanding of spin-valley-orbital physics, such as spin and valley splitting in the electronic band structure and generalized magnetoelectric responses in not only spin but also orbital and spin-orbital channels, reflecting in peculiar magnetic, elastic, and optical properties in solids.