Pressure dependence of the superconducting transition temperature in C$_6$Yb and C$_6$Ca

TL;DR

This study investigates how hydrostatic pressure affects the superconducting transition temperatures in C$_6$Yb and C$_6$Ca, revealing linear increases up to certain pressures and potential mechanisms behind the behavior.

Contribution

It provides detailed pressure-temperature phase diagrams for C$_6$Yb and C$_6$Ca, showing the pressure dependence of their superconducting transition temperatures and discussing possible pairing mechanisms.

Findings

Superconducting T_c increases linearly with pressure up to 1.2 GPa.

C$_6$Yb's T_c peaks at around 1.8 GPa before decreasing.

Pressure dependence may be explained by a plasmon pairing mechanism.

Abstract

We have studied the evolution, with hydrostatic pressure, of the recently discovered superconductivity in the graphite intercalation compounds C$_6$Yb and C$_6$Ca. We present pressure-temperature phase diagrams, for both superconductors, established by electrical transport and magnetization measurements. In the range 0-1.2 GPa the superconducting transition temperature increases linearly with pressure in both materials with $dT_c/dP = +0.39 K/GPa$ and $dT_c/dP = +0.50 K/GPa$ for C$_6$Yb and C$_6$Ca respectively. The transition temperature in C$_6$Yb, which has beenmeasured up to 2.3 GPa, reaches a peak at around 1.8 GPa and then starts to drop. We also discuss how this pressure dependence may be explained within a plasmon pairing mechanism.