Unconventional Pressure Dependence of the Superfluid Density in the Nodeless Topological Superconductor α-PdBi2

We investigated the superconducting properties of the topological superconductor α-PdBi2 at ambient and external pressures up to 1.77 GPa using muon spin rotation experiments. The ambient pressure measurements evince a fully gapped s-wave superconducting state in the bulk of the specimen. Alternating current magnetic susceptibility and muon spin rotation measurements manifest a continuous suppression of Tc with increasing pressure. In parallel, we observed a significant decrease of superfluid density by ∼20% upon application of external pressure. Remarkably, the superfluid density follows a linear relation with Tc, which was found before in some unconventional topological superconductors and hole-doped cuprates. This finding signals a possible crossover from Bose-Einstein to Bardeen-Cooper-Schrieffer like condensation in α-PdBi2.