Ordered phases and superconductivity in two-dimensional electron systems subject to pair spin-orbit interaction

TL;DR

This paper explores how pair spin-orbit interaction influences ordered phases and superconductivity in two-dimensional electron systems, revealing novel paired density wave states and a blend of Amperean pairing with finite-momentum pairing.

Contribution

It introduces the concept of paired density waves and mixed pairing states induced by pair spin-orbit interaction in 2D electron systems.

Findings

Charge-density and spin-vorticity wave orderings in non-superconducting states

Emergence of finite-momentum paired density wave superconductivity

Presence of mixed Amperean and density wave pairing states

Abstract

Pair spin-orbit interaction can emerge in strongly-interacting systems characterized by a large spin-orbit coupling. Here we study the role of this interaction in stabilizing ordered and unconventional superconducting phases. We find that, if the system avoids superconductivity, the order realized is a combination of charge-density and spin-vorticity waves. The latter is reminiscent of a loop-current state, albeit in the spin, rather in the charge, channel. If the system becomes superconducting, the order parameter assumes the form of a paired density wave, i.e. pairing occurs at finite momentum. Intriguingly, one of the possible pairings acquires a form analogous to Amperean superconductivity. However, the order parameter here is always a blend of paired density wave and Amperean pairing, rather than being purely one or the other.