Gap function of hexagonal pnictide superconductor SrPtAs (Vol. 45 No.4)

Above: Quasiparticle equal energy (ω) surfaces for A1g(a) and Eg(b) gap functions at ω/Δ0=0.5 (Δ0 is the gap amplitude). Below: QPI spectrum (c,d) for corresponding gap functions. The scattering vectors qi are characteristic for the nodal gap structure.

The pnictide superconductor SrPtAs has a hexagonal layered structure that breaks in-plane inversion symmetry while overall the crystal is still centrosymmetric. This has peculiar consequences for the electronic structure as well as the Cooper pairing. It leads to a strong Rashba spin orbit coupling and splitting of quasi-2D 5d Pt bands that dominate the Fermi surface. Although the superconducting gap functions are even or odd under inversion the in-plane pairing is nevertheless a mixture of singlet and triplet pairs due to the large Rashba coupling. Microscopic theories have obtained possible s+f and p+d wave candidates with unconventional nodal structure. We propose to apply Bogoliubov quasiparticle interference (QPI) technique to SrPtAs which records the spectral density fluctuations at the surface due to impurities. We show that their analysis can give important clues on the nodal structure of the unknown SrPtAs gap function.

A. Akbari and P. Thalmeier, “Gap function of hexagonal pnictide superconductor SrPtAs from quasiparticle interference spectrum”, EPL, 106, 27006 (2014)