High pressure phase diagrams of CeRhIn$_5$ and CeCoIn$_5$ studied by ac calorimetry

TL;DR

This study maps the pressure-temperature phase diagrams of CeRhIn$_5$ and CeCoIn$_5$ using ac calorimetry, revealing details about their magnetic and superconducting transitions and the effects of pressure on their phases.

Contribution

It provides new, detailed phase diagrams under hydrostatic pressure, clarifies the nature of phase transitions, and examines the coexistence and suppression of superconductivity in these heavy fermion compounds.

Findings

Superconductivity in CeRhIn$_5$ appears inhomogeneously below 1.95 GPa.

Homogeneous bulk superconductivity in CeRhIn$_5$ is only observed above 1.95 GPa.

The specific heat anomaly at T_c in CeCoIn$_5$ decreases linearly with pressure up to 3 GPa.

Abstract

The pressure-temperature phase diagrams of the heavy fermion antiferromagnet CeRhIn$_5$ and the heavy fermion superconductor CeCoIn$_5$ have been studied under hydrostatic pressure by ac calorimetry and ac susceptibility measurements using diamond anvil cells with argon as pressure medium. In CeRhIn$_5$, the use of a highly hydrostatic pressure transmitting medium allows for a clean simultaneous determination by a bulk probe of the antiferromagnetic and superconducting transitions. We compare our new phase diagram with the previous ones, discuss the nature (first or second order) of the various lines, and the coexistence of antiferromagnetic order and superconductivity. The link between the collaps of the superconducting heat anomaly and the broadening of the antiferromagnetic transition points to an inhomogeneous appearence of superconductivity below $P_c \approx 1.95$ GPa. Homogeneous bulk superconductivity is only observed above this critical pressure. We present a detailed analysis of the influence of pressure inomogeneities on the specific heat anomalies which emphasizes that the observed broadening of the transitions near $P_c$ is connected with the first order transition. For CeCoIn$_5$ we show that the large specific heat anomaly observed at $T_c$ at ambient pressure is suppressed linearly at least up to 3 GPa.