A Field-directional Specific Heat Study on the Gap Structure of Overdoped Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$

TL;DR

This study investigates the anisotropic behavior of the electronic specific heat in overdoped Ba(Fe_{1-x}Co_x)_2As_2 under magnetic fields, revealing insights into the gap structure and node topology.

Contribution

It provides the first detailed field-directional specific heat measurements on overdoped Ba(Fe_{1-x}Co_x)_2As_2, revealing anisotropic responses related to the superconducting gap structure.

Findings

Field dependence of {b3}(H) is larger along the c-axis than in-plane.

Minimal difference in {b3}(H) when rotating magnetic field within the ab-plane.

Results suggest that many line nodes are not excited by in-plane magnetic fields.

Abstract

Low-temperature specific heat is measured on the overdoped Ba(Fe_{1-x}Co_x)_2As_2 (x = 0.13) single crystal under magnetic fields along three different directions. A clear anisotropy is observed on the field dependent electronic specific heat coefficient {\gamma}(H). The value of {\gamma}(H) is obviously larger with magnetic field along [001] (c-axis) than that within the ab-plane of the crystal lattice, which cannot be attributed to the effect by anisotropy of the upper critical field. Meanwhile, the data show a rather small difference when the direction of the field is rotated from [100] to [110] direction within the ab-plane. Our results suggest that a considerable part of the line nodes is not excited to contribute to the quasiparticle density of states by the field when the field is within the ab-plane. The constraints on the topology of the gap nodes are discussed based on our observations.