Spin Orbit Magnetism and Unconventional Superconductivity

TL;DR

This paper uncovers an exotic spin excitation in 2D spin orbit magnetism that leads to a potential p-wave superconducting state, and explores related instabilities in 3D systems.

Contribution

It introduces a novel magnetic Fermi liquid state with a unique spin current order and analyzes its excitations and instabilities in both 2D and 3D systems.

Findings

Discovery of a $ oot q$ mode in 2D spin orbit magnetism.

Identification of a superconducting instability with p-wave symmetry.

Prediction of a Lifshitz-like instability in 3D magnetic systems.

Abstract

We find an exotic spin excitation in a magnetically ordered system with spin orbit magnetism in 2D, where the order parameter has a net spin current and no net magnetization. Starting from a Fermi liquid theory, similar to that for a weak ferromagnet, we show that this excitation emerges from an exotic magnetic Fermi liquid state that is protected by a generalized Pomeranchuck condition. We derive the propagating mode using the Landau kinetic equation, and find that the dispersion of the mode has a $\sqrt q$ behavior in leading order in 2D. We find an instability toward superconductivity induced by this exotic mode, and a further analysis based on the forward scattering sum rule strongly suggests that this superconductivity has p-wave pairing symmetry. We perform similar studies in the 3D case, with a slightly different magnetic system and find that the mode leads to a Lifshitz-like instability most likely toward an inhomogeneous magnetic state in one of the phases.