Thermodynamic properties of Ba1-xMxFe2As2 (M = La and K)

TL;DR

This study measures the specific heat of various BaFe2As2-based compounds, revealing structural, magnetic, and superconducting transitions, with the highest observed specific heat peak at the superconducting transition for K-doped samples.

Contribution

It provides detailed specific heat data for BaFe2As2 compounds, highlighting the relationship between doping, structural transitions, and superconductivity, including the highest peak observed at T_c among iron-based superconductors.

Findings

Sharp peak at 136 K for undoped BaFe2As2 indicating structural/magnetic transition

Smaller peak at 120 K for electron-doped Ba0.7La0.3Fe2As2 suggesting similar transitions

Highest specific heat peak at T_c = 36 K for hole-doped Ba0.5K0.5Fe2As2

Abstract

The specific heat $C(T)$ of BaFe$_2$As$_2$ single crystal, electron-doped Ba$_{0.7}$La$_{0.3}$Fe$_2$As$_2$ and hole-doped Ba$_{0.5}$K$_{0.5}$Fe$_2$As$_2$ polycrystals were measured. For undoped BaFe$_2$As$_2$ single crystal, a very sharp specific heat peak was observed at 136 K. This is attributed to the structural and antiferromagnetic transitions occurring at the same temperature. $C(T)$ of the electron-doped non-superconducting Ba$_{0.7}$La$_{0.3}$Fe$_2$As$_2$ also shows a small peak at 120 K, indicating a similar but weaker structural/antiferromagnetic transition. For the hole-doped superconducting Ba$_{0.5}$K$_{0.5}$Fe$_2$As$_2$, a clear peak of $C/T$ was observed at $T_c$ = 36 K, which is the highest peak seen at superconducting transition for iron-based high-$T_c$ superconductors so far. The electronic specific heat coefficient $\gamma$ and Debye temperature $\Theta_D$ of these compounds were obtained from the low temperature data.