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

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.