Finite-momentum bound pairs of two electrons in an altermagnetic metal

TL;DR

This paper investigates how altermagnetic spin-splitting leads to finite-momentum electron pairs, providing insights into unconventional superconductivity with mixed pairing symmetries in a square lattice model.

Contribution

It demonstrates the formation of finite-momentum bound pairs in an altermagnetic system, revealing a potential mechanism for altermagnetism-induced FFLO superconductivity and mixed pairing states.

Findings

Finite-momentum bound pairs arise due to altermagnetic spin-splitting.

Strong nearest-neighbor attraction leads to mixed spin-singlet and triplet pairs.

The results suggest a new pathway for unconventional superconductivity in altermagnetic materials.

Abstract

We solve the two-electron problem on a square lattice with $d$-wave altermagnetism, considering both on-site and nearest-neighbor attractive interactions. The altermagnetic spin-splitting in the single-particle dispersion naturally gives rise to a ground state of two-electron bound pairs with nonzero center-of-mass momentum. This finite-momentum pairing can be interpreted as a two-body mechanism underlying the recently proposed altermagnetism-induced Fulde--Ferrell--Larkin--Ovchinnikov (FFLO) superconducting state. Additionally, when the nearest-neighbor attraction is strong, the resulting finite-momentum bound pairs exhibit a mixture of both spin-singlet and spin-triplet characteristics, suggesting the possibility of unconventional superconductors, where spin-singlet and spin-triplet pairings coexist.