Superconductivity In K- And Na- Doped Bafe2as2: What Can We Learn From Heat Capacity And Pressure Dependence of Tc

TL;DR

This study investigates how heat capacity and pressure influence the superconducting transition temperature in K- and Na-doped BaFe2As2, revealing changes in superconducting states and deviations from known scaling laws.

Contribution

It provides new insights into the pressure and doping effects on superconductivity, highlighting a significant change in the superconducting state for high K-doping levels.

Findings

Deviations from BNC scaling for x > 0.7 in K-doped samples.

Non-linear pressure dependence of Tc near x=0.2-0.25 in Na-doped samples.

Evidence of phase boundary crossing affecting Tc in Na-doped series.

Abstract

A brief overview of changes in the superconducting transition temperature under pressure and evolution of specific heat capacity jump at Tc for two related families of iron - based superconductors, Ba{1-x}KxFe2As2 (0.2 < x < 1.0) and Ba{1-x}NaxFe2As2 (0.2 < x < 0.9) will be given. For Ba{1-x}KxFe2As2 the specific heat capacity jump at Tc measured over the whole extent of the superconducting dome shows clear deviation from the empirical, Delta Cp (Tc) ~ Tc^3, scaling (known as the BNC scaling) for x > 0.7. At the same concentrations range apparent equivalence of effects of pressure and K- substitution on Tc fails. These observations suggests a significant change of the superconducting state for x > 0.7. In contrast, the data for the large portion of Ba{1-x}NaxFe2As2 (0.2 < x < 0.9) series follow the BNC scaling. However, the pressure dependence of Tc (measured up to ~ 12 kbar) have clear non-linearities for Na concentration in 0.2 - 0.25 region, that may be consistent with Tc crossing the phase boundaries of the emergent, narrow, antiferromagnetic/tetragonal phase. Results will be discussed in context other studies of these two and related families of iron-based superconductors.