Monolayer FeSe on SrTiO3, which exhibits high-temperature superconductivity, has recently been proposed to additionally possess (Néel) antiferromagnetic order. This magnetic order, however, breaks both inversion and time-reversal symmetry, the two symmetries guaranteeing a weak-coupling superconducting transition in three dimensions. Motivated by this finding, I will reexamine the minimal symmetries protecting superconductivity in two dimensions and the resulting order parameters. I will show that having a combination of either symmetry with a mirror operation on the basal plane is sufficient in two dimensions and discuss a minimal model with only one of the symmetries present. Finally, I will apply these considerations to the case of FeSe. Interestingly, despite having both combined symmetries, only one superconducting state is fully stable in antiferromagnetic FeSe, namely a chiral spin-triplet order, while any phonon-mediated s-wave order is strongly suppressed by the local ordered moments.

連絡教員 物理学系 古賀 昌久（内線2727）