Interaction induced staggered spin-orbit order in two-dimensional electron gas

TL;DR

This paper introduces a new emergent phase in two-dimensional Fermi gases where interaction-driven spin-orbit order causes a large quasiparticle gap and chiral states, with potential applications in spintronics.

Contribution

It formulates a novel interaction-induced staggered spin-orbit order in 2D Fermi gases, revealing a spontaneous symmetry breaking and large quasiparticle gap due to Fermi surface nesting.

Findings

Identification of a spin-orbit density wave state.

Large quasiparticle gap with chiral electronic states.

Potential realization in BiAg₂ surface states.

Abstract

We propose and formulate an interaction induced staggered spin-orbit order as a new emergent phase of two-dimensional Fermi gases. We show that when some form of inherent spin-splitting via Rashba-type spin-orbit coupling renders two helical Fermi surfaces to become significantly `nested', a Fermi surface instability arises. To lift this degeneracy, a spontaneous symmetry breaking spin-orbit density wave develops, causing a surprisingly large quasiparticle gapping with chiral electronic states. Since the staggered spin-orbit order is associated with a condensation energy, quantified by the gap value, destroying such spin-orbit interaction costs sufficiently large perturbation field or temperature or de-phasing time. BiAg$_2$ surface state is shown to be a representative system for realizing such novel spin-orbit interaction with tunable and large strength, and the spin-splitting is decoupled from charge excitations. These functional properties are relevant for spin-electronics, spin-caloritronics, and spin-Hall effect applications.