Superconducing gap structure in altermagnets

Altermagnetic metals break time-reversal symmetry and feature spin-split Fermi surfaces generated by compensated Néel-ordered collinear magnetic moments. Being metallic, such altermagnets may undergo a further instability at low temperatures to a superconducting state, and it is an interesting open question what are the salient features of such altermagnetic superconductors? We address this question on the basis of realistic microscopic models that capture the altermagnetic sublattice degrees of freedom. We find that the sublattice structure can strongly affect the superconducting gap structure in altermagnetic superconductors. In particular, it imposes nodes in the gap on the Brillouin zone edges for superconductors stabilized by momentum-independent bare attraction channels. We contrast this to the case of nearest-neighbor pairing where pairing is allowed on the Brillouin zone edges and $d$-wave gap structures can be favored. Finally we dicuss the emergence of equal-spin triplet order and the imprint of the altermagnetic spin-splittng on the nonunitary d-vector cross product.