Effect of annealing on the specific heat of Ba(Fe1-xCox)2As2

TL;DR

This study investigates how annealing affects the specific heat and superconducting properties of Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$ across different doping levels, revealing improved sample quality and insights into the superconducting gap structure.

Contribution

It demonstrates that annealing enhances superconducting characteristics and clarifies the gap structure in electron-doped Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$, providing a self-consistent analysis within an extended s-wave pairing framework.

Findings

Annealing increases $T_c$ and reduces $ ho_0$ in the superconducting state.

Sample quality influences the observed low-temperature power laws.

Optimal doping shows a fully gapped superconductor, while under and overdoped samples suggest nodal structures.

Abstract

We report on the effect of annealing on the temperature and field dependencies of the low temperature specific heat of the electron-doped Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$ for under-(x = 0.045), optimal- (x = 0.08) and over-doped (x = 0.105 and 0.14) regimes. We observed that annealing significantly improves some superconducting characteristics in Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$. It considerably increases $T_{c}$, decreases $\gamma_{0}$ in the superconducting state and suppresses the Schottky-like contribution at very low temperatures. The improved sample quality allows for a better identification of the superconducting gap structure of these materials. We examine the effects of doping and annealing within a self-consistent framework for an extended s-wave pairing scenario. At optimal doping our data indicates the sample is fully gapped, while for both under and overdoped samples significant low-energy excitations possibly consistent with a nodal structure remain. The difference of sample quality offers a natural explanation for the variation in low temperature power laws observed by many techniques.