We report measurements of the in-plane London penetration depth $\lambda$ in single crystals of the $\alpha$-PdBi$_{ 2}$ superconductor --- the $\alpha$-phase counterpart of the putative topological superconductor $\beta$-PdBi$_{ 2}$, down to 0.35~K using a high-resolution tunnel-diode-based technique. Both $\lambda$ and superfluid density $\rho_{ s}$ exhibit an exponential behavior for $T\leq$ 0.35$T_{ c}$, with $\Delta(0)/k_{ B}T_{ c}\sim$2.0, $\Delta C/\gamma T_{ c}$$\sim$2.0 and $\lambda(0)$$\sim$140~nm, showing that $\alpha$-PdBi$_{ 2}$ is a moderately-coupling, fully-gapped superconductor. The values of $\Delta(0)$ and $\Delta C/\gamma T_{ c}$ are consistent with each other via strong-coupling corrections.
Categories: cond-mat.supr-con