Pressure-induced enhancement of superconductivity and superconducting-superconducting transition in CaC$\_6$

TL;DR

This study investigates how applying high pressure up to 16 GPa affects the superconducting transition temperature and properties of CaC₆, revealing a phase transition and significant changes in resistivity.

Contribution

It provides new insights into pressure-induced phase transitions and superconducting behavior in CaC₆, including a transition between two distinct superconducting phases.

Findings

$T_c$ increases from 11.5 K to 15.1 K at 8 GPa

$T_c$ drops to 5 K above 10 GPa

Resistivity increases by approximately 200 times after 8 GPa

Abstract

We measured the electrical resistivity, $\varrho(T)$, of superconducting CaC$\_6$ at ambient and high pressure up to 16 GPa. For $P \leq$8 GPa, we found a large increase of $T\_c$ with pressure from 11.5 up to 15.1 K. At 8 GPa, $T\_c$ drops and levels off at 5 K above 10 GPa. Correspondingly, the residual $\varrho$ increases by $\approx$ 200 times and the $\varrho(T)$ behavior becomes flat. The recovery of the pristine behavior after depressurization is suggestive of a phase transition at 8 GPa between two superconducting phases with good and bad metallic properties, the latter with a lower $T\_c$ and more static disorder.