Phase-modulated superconductivity via altermagnetism

TL;DR

This paper demonstrates that altermagnetism can induce a phase-modulated superconducting state, expanding understanding of superconductivity in magnetic materials without external magnetic fields.

Contribution

It develops a Ginzburg--Landau theory showing how altermagnetic spin splitting stabilizes phase-modulated superconductivity, a novel mechanism compared to traditional Zeeman effects.

Findings

Phase-modulated superconductivity is stabilized by altermagnetic spin splitting.

Multisublattice structures are essential for realizing this exotic state.

Altermagnets are promising platforms for superconductivity without external magnetic fields.

Abstract

Stimulated by recent interest in altermagnets, a novel class of antiferromagnets with macroscopic time-reversal symmetry breaking, we investigate the coexistence of altermagnetism and superconductivity. By developing a Ginzburg--Landau theory based on microscopic models, we show that a phase-modulated Fulde--Ferrell superconducting state is stabilized via altermagnetic spin splitting, in contrast to the typical amplitude-modulated states that occur under the uniform Zeeman field. We apply our framework to different models to compare the resulting phase diagrams: a two-sublattice model with altermagnetic order, a continuum model with an anisotropic Zeeman field mimicking altermagnetic spin splitting, and a conventional square-lattice model with two kinds of anisotropic Zeeman fields. We show that the multisublattice structure is crucial for realizing the phase-modulated superconductivity, and highlight spin-split altermagnets as a promising platform for exploring this exotic superconductivity without external magnetic fields.