Specific Heat and the Gap Structure of a Nematic Superconductor, application to FeSe

We report the results of our in-depth analysis of spectroscopic and thermodynamic properties of a multi-orbital system, like FeSe, which first develops a nematic order upon lowering temperature, and then undergoes a transition into a superconducting state, which co-exists with the nematic order. We analyze the the angular dependence of the gap function and the behavior of the specific heat C_v (T) of such nematic superconductor. Specifically, we address three issues:
(i) the relation between the angular dependence of the gap in the mixed s+d state, induced by nematicity, and orbital transmutation of low-energy fermionic excitations, (ii) interplay between contributions from different orbitals to the jump of C_v (T) at a superconducting T_c and to the temperature dependence of the specific heat below T_c, and (iii) the jump of C_v (T) at a potential transition at T_c1 < T_c from an s+d state to s + e^iα d state that breaks time-reversal symmetry.