Nodes vs. minima in the energy gap of iron-pnictides from field-induced anisotropy

TL;DR

This paper develops a formalism to analyze oscillations in specific heat and thermal transport in multiband superconductors, revealing how these oscillations inform on the gap structure of iron-pnictides.

Contribution

It introduces a new theoretical approach to interpret experimental oscillation data, highlighting the presence of anisotropic gaps with deep minima or nodes in iron-pnictides.

Findings

Oscillations change sign at low temperatures and fields.

Experimental data suggest anisotropic gaps with deep minima or nodes.

Predictions for thermal conductivity behavior to distinguish gap structures.

Abstract

We develop the formalism for computing the oscillations of the specific heat and thermal transport under rotated magnetic field in multiband superconductors with anisotropic gap and apply it to iron-pnictides. We show that these oscillations change sign at low temperatures and fields, which strongly influences the conclusions about the gap structure based on experiment. We find that recent measurements of the specific heat oscillations indicate that the iron-based superconductors possess an anisotropic gap with deep minima or nodes close to the line connecting electron and hole pockets. We make predictions for the behavior of the thermal conductivity that will help distinguish between these cases.