Low-Energy Quasiparticles Probed by Heat Transport in the Iron Based Superconductor LaFePO

TL;DR

This study investigates low-energy quasiparticles in LaFePO using heat transport measurements, revealing evidence for a sign-changing nodal s+/- superconducting state through thermal conductivity behavior at very low temperatures.

Contribution

It provides experimental evidence supporting a nodal s+/- pairing symmetry in LaFePO based on thermal conductivity data at ultra-low temperatures and magnetic fields.

Findings

Large residual linear thermal conductivity indicates low-energy quasiparticles.

Unusual supralinear temperature dependence suggests nodal superconductivity.

High scattering rate with minimal Tc suppression supports s+/- pairing symmetry.

Abstract

We have measured the thermal conductivity of the iron pnictide superconductor LaFePO down to temperatures as low as T=60mK and in magnetic fields up to 5 T. The data shows a large residual contribution that is linear in temperature, consistent with the presence of low energy electronic quasiparticles. We interpret the magnitude of the linear term, as well as the field and temperature dependence of thermal transport in several pairing scenarios. The presence of an unusual supralinear temperature dependence of the electronic thermal conductivity in zero magnetic field, and a high scattering rate with minimal Tc suppression argues for a sign-changing nodal s+/- state.