Orbital-dependent pairing effects in the nuclear spin–lattice relaxation rate ofSr2RuO4

Abstract

The p-wave chiral superconductorSr2RuO4 is a quasi-two-dimensional, highly anisotropic system with three bands crossingthe Fermi energy. Low temperature power law behaviour is observed intemperature-dependent physical properties, including specific heat, penetrationdepth and NMR relaxation rate, which is consistent with the existence of a line ofnodes in the quasiparticle gap. However, the interpretation of these experiments iscomplicated by possible temperature dependences arising from the multi-band ororbital-dependent paring. In this paper we have calculated the NMR relaxation rate1/T1 onthe basis of a realistic orbital-specific, three-orbital, three-dimensional model with phenomenologicalcoupling constants. The model leads to the ground state with chiral–gapless order parameter on theγ sheet of the Fermi level and with nodes on the remaining twosheets. Our results compare well with existing experimental101Ru NQR data showinga relaxation rate 1/T1∼T3 and no visible Hebel–Slichter-like peak belowTc. On the otherhand, the diagonal dxy orbital projected components of the relaxation rate show a morecomplex behaviour, including a Hebel–Slichter-like peak belowTc. We speculate that these orbital dependences might be relatedto the differences observed between spin relaxation rates for17O and 101Ru nuclei in this material.