Evidence for +-s-wave pairing symmetry in LiFeAs: specific heat study

TL;DR

This study uses specific heat measurements to investigate the superconducting gap symmetry in LiFeAs, providing evidence supporting a multiband  s-wave pairing state over a nodal d-wave gap.

Contribution

The paper presents specific heat data indicating LiFeAs has a multiband  s-wave superconducting gap, clarifying its pairing symmetry.

Findings

Small specific heat jump at Tc suggests strong scattering effects.

Magnetic field dependence of  supports multiband  s-wave gap.

Low-temperature specific heat behavior argues against nodal d-wave symmetry.

Abstract

We report specific heat capacity measurements on a LiFeAs single crystal at temperatures down to 400 mK and magnetic fields up to 9 Tesla. A small specific heat jump at Tc and finite residual density of states at T=0 K in the superconducting (SC) state indicate that there are strong unitary scatterers that lead to states within the SC gap. A sub-linear magnetic field dependence of the Sommerfeld coefficient \gamma(H) at T=0 K is equally well fitted by both a nodal d-wave gap as well as a sign changing multiband \pm s-wave gap. When impurity effects are taken into account, however, the linear temperature dependence of the electronic specific heat C_{el}/T at low temperatures argues against a nodal d-wave superconducting gap. We conclude that the SC state of LiFeAs is most compatible with the multiband \pm s-wave SC state with the gap values \Delta_{small}=0.46 \Delta_{large}.