Nematic and chiral superconductivity induced by odd-parity fluctuations

Recent experiments indicate that superconductivity in Bi₂Se₃ intercalated with Cu, Nb, or Sr is nematic with rotational symmetry breaking. Motivated by this observation, we present a model study of nematic and chiral superconductivity induced by odd-parity fluctuations. We show that odd-parity fluctuations in the two-component E_u representation of D_3d crystal point group can generate attractive interaction in both the even-parity s-wave and odd-parity E_u pairing channels, but repulsive interaction in other odd-parity pairing channels. Coulomb repulsion can suppress s-wave pairing relative to E_u pairing, and thus the latter can have a higher critical temperature. E_u pairing has two distinct phases: a nematic phase and a chiral phase, both of which can be realized in our model. When s-wave and E_u pairings have similar instability temperature, we find an intermediate phase in which both types of pairing coexist.