Intra-unit-cell singlet pairing mediated by altermagnetic fluctuations

TL;DR

This paper explores how altermagnetic fluctuations induce diverse superconducting pairing states, including intra-unit-cell pairing with complex topological properties, emphasizing the importance of sublattice structure in these phenomena.

Contribution

It reveals that altermagnetic fluctuations can lead to intra-unit-cell pairing with various symmetries and topological features, highlighting the role of sublattice degrees of freedom.

Findings

Short-range fluctuations favor intra-unit-cell pairing.

Coexistence with altermagnetic order can produce topologically non-trivial superconductivity.

Different Fermi surface shapes lead to various pairing symmetries.

Abstract

We investigate the superconducting instabilities induced by altermagnetic fluctuations. Because of the non-trivial sublattice structure of the altermagnetic order, shorter-range and longer-range fluctuations favor qualitatively different types of pairing states. Specifically, while the latter stabilize a standard spin-triplet $p$-wave state, just like ferromagnetic fluctuations, the former leads to intra-unit-cell pairing, in which the Cooper pairs are formed by electrons from different sublattices. The symmetry of the intra-unit-cell gap function can be not only $p$-wave, but also spin-singlet $s$-wave and $d$-wave, depending on the shape of the Fermi surface. We also show that coexistence with altermagnetic order promotes intrinsic non-trivial topology, such as protected Bogoliubov Fermi surfaces and higher-order topological superconductivity. Our work establishes the key role played by sublattice degrees of freedom in altermagnetic-fluctuation mediated interactions.