Unconventional pressure dependence of the superfluid density in the nodeless topological superconductor $\alpha$-PdBi$_2$

TL;DR

This study explores how pressure affects the superfluid density and critical temperature in the topological superconductor $ extalpha$-PdBi$_2$, revealing unconventional behavior and potential BEC-BCS crossover.

Contribution

It provides the first detailed pressure-dependent muon spin rotation analysis of $ extalpha$-PdBi$_2$, highlighting an unusual pressure dependence of superfluid density and $T_c$ in a nodeless topological superconductor.

Findings

Superfluid density decreases by ~20% under pressure.

Superfluid density linearly correlates with $T_c$, indicating unconventional behavior.

Evidence suggests a possible BEC-BCS crossover in $ extalpha$-PdBi$_2$.

Abstract

We investigated the superconducting properties of the topological superconductor $\alpha$--PdBi$_2$ at ambient and external pressures up to 1.77~GPa using muon spin rotation ($\mu$SR) experiments. The ambient pressure measurements evince a fully gapped $s$-wave superconducting state in the bulk of the specimen. AC magnetic susceptibility and $\mu$SR measurements manifest a continuous suppression of $T_{\rm c}$ with increasing pressure. In parallel, we observed a significant decrease of superfluid density by $\sim$20\% upon application of external pressure. Remarkably, the superfluid density follows linear relation with $T_{\rm c}$ which was found before in some unconventional topological superconductors and hole doped cuprates. This finding signals a possible crossover from BEC to BCS in $\alpha$--PdBi$_2$.