Nodal gap structure of BaFe_2(As_{1-x}P_x)_2 from angle-resolved thermal conductivity in a magnetic field

TL;DR

This study uses angle-resolved thermal conductivity measurements to investigate the nodal gap structure in the iron-pnictide superconductor BaFe2(As0.67P0.33)2, revealing evidence for closed nodal loops on the electron Fermi surface.

Contribution

It provides the first detailed experimental evidence for the specific nodal gap structure in this compound using angle-resolved thermal conductivity.

Findings

Thermal conductivity shows fourfold oscillations with minima at ±45°

Data consistent with closed nodal loops on the electron Fermi surface

Nodal structure linked to high Fermi velocity regions

Abstract

The structure of the superconducting order parameter in the iron-pnictide superconductor BaFe$_2$(As$_{0.67}$P$_{0.33}$)$_2$ ($T_c=31$\,K) with line nodes is studied by the angle-resolved thermal conductivity measurements in a magnetic field rotated within the basal plane. We find that the thermal conductivity displays distinct fourfold oscillations with minima when the field is directed at $\pm45^\circ$ with respect to the tetragonal a-axis. We discuss possible gap structures that can account for the data, and conclude that the observed results are most consistent with the closed nodal loops located at the flat parts of the electron Fermi surface with high Fermi velocity.