Interplay between Superconductivity and Altermagnetism in Disordered Materials and Heterostructures

TL;DR

This paper explores the complex interaction between superconductivity and altermagnetism in disordered materials, revealing novel effects like a nonlinear magnetoelectric response and proximity-induced magnetization, with implications for hybrid superconductor-altermagnet structures.

Contribution

The study derives new theoretical insights into how superconductivity couples with altermagnetism, including effects on magnetization and phase transitions in hybrid structures.

Findings

Identification of a nonlinear magnetoelectric effect induced by supercurrents.

Prediction of proximity-induced magnetization in superconductor-altermagnet hybrids.

Analysis of $0$-$ extpi$ transitions in Josephson junctions with coexisting effects.

Abstract

We study the interplay between superconductivity and altermagnetism in disordered systems using recently derived quantum kinetic transport equations. Starting from this framework, we derive the Ginzburg-Landau free energy and identify, in addition to the conventional pair-breaking term, a coupling between the spin and the spatial variation of the superconducting order parameter. Two distinct effects emerge from this coupling. The first is a nonlinear magnetoelectric effect, in which a supercurrent (i.e., a phase gradient) induces a spin texture; this contribution is quadratic in the phase gradient. The second effect arises when the magnitude, rather than the phase, of the superconducting order parameter varies in space, likewise leading to a finite magnetization. We show that these two contributions compete in the case of an Abrikosov vortex, where both the amplitude and phase of the order parameter vary spatially. The effect associated with amplitude variations also gives rise to a proximity-induced magnetization (PIM) in hybrid structures composed of a superconductor (S) and an altermagnet (AM). Using quasiclassical theory, we analyze the PIM in diffusive S/AM bilayers and S/AM/S Josephson junctions, and determine the induced magnetization profiles. In Josephson junctions, where both the PIM and the nonlinear magnetoelectric effect coexist, we further predict the occurrence of $0$-$\pi$ transitions.