Identifying the pairing symmetry in the Sr2RuO4 superconductor

TL;DR

This study analyzes heat capacity and thermal conductivity data of Sr2RuO4, concluding that a nodal order parameter, likely an odd parity spin-triplet or even parity spin-singlet state, best explains the low-temperature behavior.

Contribution

It provides evidence for a nodal superconducting gap in Sr2RuO4 and suggests specific pairing symmetries, proposing further experiments to distinguish between candidates.

Findings

Nodal lines are necessary to explain low-temperature data.

Gapped order parameters are inconsistent with thermodynamic and transport measurements.

Spin-fluctuation mechanism favors pairing states with gap maxima along zone diagonals.

Abstract

We have analyzed heat capacity and thermal conductivity measurements of Sr2RuO4 in the normal and superconducting state and come to the conclusion that an order parameter with nodal lines on the Fermi surface is required to account for the observed low-temperature behavior. A gapped order parameter is inconsistent with the reported thermodynamic and transport data. Guided by a strongly peaked dynamical susceptibility along the diagonals of the Brillouin zone in neutron scattering data, we suggest a spin-fluctuation mechanism that would favor the pairing state with the gap maxima along the zone diagonals (such as for a d_{xy} gap). The most plausible candidates are an odd parity, spin-triplet, f-wave pairing state, or an even parity, spin-singlet, d-wave state. Based on our analysis of possible pairing functions we propose measurements of the ultrasound attenuation and thermal conductivity in the magnetic field to further constrain the list of possible pairing states.