Specific heat and gap structure of a nematic superconductor: Application to FeSe

Abstract

We report the results of our in-depth analysis of spectroscopic and thermodynamic properties of a multiorbital metal, like FeSe, which first develops a nematic order and then undergoes a transition into a superconducting state, which coexists with nematicity. We analyze the angular dependence of the gap function and specific heat Cv(T) of such a nematic superconductor. We specifically address three issues: (i) the angular dependence of the gap in light of the competition between the nematicity-induced s−d mixture and the orbital transmutation of low-energy excitations in the nematic state, (ii) the effect of nematicity on the magnitude of the jump of the specific heat Cv(T) at Tc and the temperature dependence of Cv(T) below Tc, and (iii) a potential transition at Tc1<Tc from an s+d state to an s+eiηd state that breaks time-reversal symmetry. We consider two scenarios for a nematic order: scenario A, in which this order develops between dxz and dyz orbitals on hole and electron pockets, and scenario B, in which there is an additional component of the nematic order for dxy fermions on the two electron pockets.

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