Thermodynamic evidence for pressure-induced bulk superconductivity in the Fe-As pnictide superconductor CaFe2As2

TL;DR

This study provides thermodynamic evidence that pressure induces bulk superconductivity in CaFe2As2, with specific-heat anomalies confirming a true superconducting state near a structural phase transition.

Contribution

It presents combined specific-heat and resistivity measurements under pressure, revealing the bulk nature of superconductivity and its relation to structural instability in CaFe2As2.

Findings

Superconductivity is confirmed as a bulk phenomenon via specific-heat anomalies.

The thermodynamic transition temperature differs from resistive onset, indicating strain effects.

Superconductivity occurs near a crystallographic phase transition.

Abstract

We report specific-heat and resistivity experiments performed in parallel in a Bridgman-type of pressure cell in order to investigate the nature of pressure-induced superconductivity in the iron pnictide compound CaFe2As2. The presence of a pronounced specific-heat anomaly at Tc reveals a bulk nature of the superconducting state. The thermodynamic transition temperature differs dramatically from the onset of the resistive transition. Our data indicates that superconductivity occurs in the vicinity of a crystallographic phase transition. We discuss the discrepancy between the two methods as caused by strain-induced superconducting precursors formed above the bulk thermodynamic transition due to the vicinity of the structural instability.