Possible pairing symmetries in SrPtAs with a local lack of inversion center

Abstract

We discuss possible pairing symmetries in the hexagonal pnictide superconductor SrPtAs. The local lack of inversion symmetry of the two distinct conducting layers in the unit cell results in a special spin-orbit coupling with a staggered structure. We classify the pairing symmetry by the global crystal point group D 3d , and suggest some candidates for the stable state using a tight-binding model with an in-plane, density-density type pairing interaction. We may have some unconventional states like s + f -wave and a mixture of chiral d-wave and chiral p-wave. The spin orbit coupling is larger than the interlayer hopping, and the mixing between spin-singlet and triplet states can be seen in spite of the fact that the system has a global inversion center.

Multigap superconductivity in locally noncentrosymmetric SrPtAs: AnAs75nuclear quadrupole resonance investigation

“…This is in general agreement with the LDA calculations, 15 that predict 74%. 5 The line node order parameter produces a much flatter curve (see Fig. 3, brown curve) than our data and a rather instant decrease, which does not match to our findings.…”

“…It is interesting how theoretical predictions, in particular for the chiral d-wave state 5,7 and the f -wave state 5,8 , compare with the present NQR study. With the knowledge of the bandstructure and a simple representation of the chiral d-wave state and the f -wave state provided by Ref.…”

“…With the knowledge of the bandstructure and a simple representation of the chiral d-wave state and the f -wave state provided by Ref. 5 , we calculated the spin-lattice relaxation rate without a variable fitting parameter for the anisotropy (in the previous model, this is the δ parameter). This is plotted in Fig.…”

“…3 A compound with a globally equivalent AlB 2 -type structure, MgB 2 , exhibits multigap superconductivity with T c ≈ 40 K. 4 The high spin-orbit coupling in SrPtAs opens the possibility for singlet-triplet mixing of the order parameter. 5 Interestingly, recent µSR experiments proved the development of a small static spontaneous internal field just below T c , evidencing time reversal symmetry (TRS) breaking in superconducting SrPtAs. 6 This fact excludes a conventional superconducting state, that preserves TRS and can not coincide with an internal magnetic field.…”

Chirald-wave superconductivity in doped graphene

“…In fact, recent muon spin-rotation (µSR) experiments have revealed that time-reversal symmetry is broken at T c [172] and several experiments have reported a lack of nodes in the quasiparticle spectrum [172,173], all consistent with a chiral d-wave state. Due to layer stacking, the point group is reduced to D 3d in SrPtAs and the crystal structure also lacks local inversion symmetry, although the unit cell possesses a global inversion center [171,174]. The Fermi surface in SrPtAs consists of both two hole pockets around Γ and electron pockets at K, K [175].…”