Multi-gap superconductivity in single crystals of Ba$_{0.65}$Na$_{0.35}$Fe$_2$As$_2$: A calorimetric investigation

TL;DR

This study reveals multi-gap superconductivity in Ba$_{0.65}$Na$_{0.35}$Fe$_2$As$_2$ single crystals through calorimetric measurements, showing two distinct s-wave gaps and providing insights into its electronic properties.

Contribution

It provides the first calorimetric evidence of two-gap superconductivity in hole-doped Ba$_{0.65}$Na$_{0.35}$Fe$_2$As$_2$, highlighting differences from other similar compounds.

Findings

Presence of two s-wave like gaps with different magnitudes

High electronic specific heat coefficient in the normal state

Superconducting transition temperature T_c = 29.4 K

Abstract

We investigate the electronic properties and the superconducting gap characteristics of a single crystal of hole-doped 122 Fe-pnictide Ba$_{0.65}$Na$_{0.35}$Fe$_2$As$_2$ by means of specific heat measurements. The specific heat exhibits a pronounced anomaly around the superconducting transition temperature $T_c$ = 29.4 K, and a small residual part at low temperature. In a magnetic field of 90 kOe, the transition is broadened and $T_c$ is lowered insignificantly by an amount $\sim$ 1.5 K. We estimate a high electronic coefficient in the normal state with a value 57.5 mJ mol$^{-1}$ K$^2$, being consistent with hole-doped 122 compounds. The temperature-dependent superconducting electronic specific heat cannot be described with single-gap BCS theory under weak coupling approach. Instead, our analysis implies a presence of two s-wave like gaps with magnitudes $\Delta_1(0)/k_BT_c$ = 1.06 and $\Delta_2(0)/k_BT_c$ = 2.08 with their respective weights of 48% and 52%. While our results have qualitative similarities with other hole-doped 122 materials, the gap's magnitude and their ratio are quite different.