Quantum Phonon Dynamics Induced Spontaneous Spin-Orbit Coupling

Abstract

Spin-orbit coupling in solids is typically a single-body effect arising from relativity. In this work, we propose a spontaneous generation of spin-orbit coupling from symmetry breaking. A spin-dependent electron-phonon coupling model is investigated on a half-filled square lattice, which is solved by sign-problem-free quantum Monte Carlo simulations. The phase diagram as function of phonon frequency $\ddot{I}‰$ and coupling constant $\hat{I}»$ is fully investigated. The spin-orbit coupling emerges as an order in the ground state for any $\hat{I}»$ in the adiabatic limit, accompanied by a breathing mode of lattice distortion and a staggered loop spin-current. This phase dominates in the entire range of $\ddot{I}‰$ with $\hat{I}»<\hat{I}{»}_{\infty }$, a critical value in the $\ddot{I}‰\to \infty$ limit. With increasing $\ddot{I}‰$ and $\hat{I}»>\hat{I}{»}_{\infty }$, the emergent spin-orbit coupling is suppressed and a phase transition occurs leading to charge-density-wave degenerate with superconductivity order. Our work opens up the possibility of hidden spin-orbit coupling in materials where it is otherwise forbidden by lattice symmetry and paves the way to explore new usable materials or devices in spintronics.

5 pages, 7 figures