Specific Heat vs Field in the 30 K Superconductor BaFe2(As0.7P0.3)2

TL;DR

This study measures the specific heat of the 30 K superconductor BaFe2(As0.7P0.3)2 and finds no evidence of nodal quasiparticles through field dependence, challenging previous interpretations of its low-energy excitations.

Contribution

The paper provides the first specific heat measurements on BaFe2(As0.7P0.3)2 that do not support the presence of order parameter nodes, contrasting prior experimental results.

Findings

C/T is linear in field at low temperatures

No evidence of Volovik effect in the measurements

Contradicts previous interpretations of low-energy excitations

Abstract

We report specific heat measurements on the Fe-based superconductor BaFe2(As0.7P0.3)2, a material on which previous penetration depth, NMR, and thermal conductivity measurements have observed a high density of low-energy excitations, which have been interpreted in terms of order parameter nodes. Within the resolution of our measurements, the low temperature limiting C/T is found to be linear in field, i.e. we find no evidence for a Volovik effect associated with nodal quasiparticles in either the clean or dirty limit. We discuss possible reasons for this apparent contradiction.