Calorimetric Evidence for Nodes in the Overdoped Ba(Fe$_{0.9}$Co$_{0.1}$)$_{2}$As$_{2}$

TL;DR

This study uses low-temperature specific heat measurements to provide calorimetric evidence for nodes in the superconducting gap of overdoped Ba(Fe$_{0.9}$Co$_{0.1}$)$_{2}$As$_{2}$, indicating complex multi-gap superconductivity.

Contribution

It offers the first calorimetric evidence supporting the presence of nodes in the superconducting gap of overdoped Ba(Fe$_{0.9}$Co$_{0.1}$)$_{2}$As$_{2}$, challenging simple isotropic gap models.

Findings

No Schottky-like upturn observed down to 400 mK.

Results consistent with multi-gap superconductivity with nodes.

Enhanced low-temperature quasiparticle excitations detected.

Abstract

We present low-temperature specific heat of the electron-doped Ba(Fe$_{0.9}$Co$_{0.1}$)$_{2}$As$_{2}$, which does not show any indication of an upturn down to 400 mK, the lowest measuring temperature. The lack of a Schottky-like feature at low temperatures or in magnetic fields up to 9 Tesla enables us to identify enhanced low-temperature quasiparticle excitations and to study anisotropy in the linear term of the specific heat. Our results can not be explained by a single or multiple isotropic superconducting gap, but are consistent with multi-gap superconductivity with nodes on at least one Fermi surface sheet.