Possibility of chiral d -wave state in the hexagonal pnictide superconductor SrPtAs

Abstract

We discuss the type of pairing in the hexagonal pnictide superconductor SrPtAs, taking into account its multiband structure. The topological chiral d-wave state with time-reversal-symmetry breaking has been anticipated from the spontaneous magnetization observed by the muon-spinrelaxation experiment. We point out in this paper that the recent experimental reports on the nuclear-spin-lattice relaxation rate T −1 1 and superfluid density ns(T ), which seemingly support the conventional s-wave pairing, are also consistent with the chiral d-wave state. The compatibility of the gap and multiband structures is crucial in this argument. We propose that the measurement of the bulk quasiparticle density of states would be useful for the distinction between two pairing states.

Superconductivity in 5dtransition metal Laves phase SrIr2

“…In these materials, the Cooper pair is expected to be the mixed state of the singlet and triplet pairing state [3]. More recently, several groups have discussed the superconductivity in the case of locally broken inversion sym metry where the global inversion symmetry is retained [4][5][6][7][8][9]. For example, SrPtAs (T c ~ 2.4 K) has an inversion symmetry in the whole unit cell, however the Pt-As layer locally lacks an inversion center [7].…”