Determining gap nodal structures in Fe-based superconductors: angle-dependence of the low temperature specific heat in an applied magnetic field

TL;DR

This paper proposes a method to determine the symmetry of the superconducting order parameter in Fe-based superconductors by measuring the angle dependence of low-temperature specific heat in a magnetic field.

Contribution

It introduces a practical experimental approach to identify the gap nodal structure using specific heat measurements and provides theoretical calculations for different candidate states.

Findings

Specific heat oscillations vary with the symmetry of the order parameter.

The method can distinguish between different gap structures based on angle dependence.

The approach is feasible with available single crystals and band structure data.

Abstract

Since the discovery of high-Tc LaO_1-xF_xFeAs, and other such systems based on FeAs layers, several proposals have been made for the superconducting order parameter Delta_k, on both phenomenological and microscopic grounds. Here we discuss how the symmetry of Delta_k in the bulk can be determined, assuming that single crystals will soon be available. We suggest that a measurement of the dependence of the low temperature specific heat on the angle of a magnetic field in the FeAs plane is the simplest such method, and calculate representative specific heat vs. field angle oscillations for the various candidate states, using a phenomenological band structure fitted to the DFT Fermi surface.