Superconducting and structural properties of the type-I superconductor PdTe2 under high pressure

TL;DR

This study investigates how high pressure affects the superconducting transition temperature and crystal structure of PdTe2, revealing a non-monotonic $T_c$ variation and possible Lifshitz transition around 1 GPa.

Contribution

The paper provides experimental evidence of pressure-induced changes in superconductivity and structure in PdTe2, including a stable crystal structure and signs of a Lifshitz transition at 1 GPa.

Findings

$T_c$ decreases monotonically from 1.8 K to 0.82 K between 1 and 5.5 GPa

Crystal structure remains stable up to 8 GPa

Possible Lifshitz transition indicated by pressure-strain analysis

Abstract

The transition metal dichalcogenide PdTe$_2$ has attractive features based on its classification as a type-II Dirac semimetal and the occurrence of type-I superconductivity, providing a platform for discussion of a topological superconductor. Our recent work revealed that type-I superconductivity persists up to pressures of $\sim2.5$ GPa and the superconducting transition temperature $T_{\rm c}$ reaches a maximum at around 1 GPa, which is inconsistent with the theoretical prediction. To understand its non-monotonic variation and investigate superconductivity at higher pressures, we performed structural analysis by x-ray diffraction at room temperature below 8 GPa and electrical resistivity measurements at low temperatures from 1 to 8 GPa. With regard to the superconductivity beyond 1 GPa, the monotonic decrease in $T_{\rm c}$ is reproduced without any noticeable anomalies; $T_{\rm c}$ changes from 1.8 K at 1 GPa to 0.82 K at 5.5 GPa with $dT_{\rm c}/dP\sim-0.22$ K/GPa. The crystal structure with spacegroup $P$\={3}$m$1 is stable in the pressure range we examined. On the other hand, the normalized pressure-strain analysis (finite strain analysis) indicates that the compressibility changes around 1 GPa, suggesting that a Lifshitz transition occurs. We here discuss the effect of pressure on the superconducting and structural properties based on the comparison of these experimental results.