Transport properties in normal-metal Bi 2 Pd 3 S 2 and superconducting Bi 2 Pd 3 Se 2

The transport properties of the parkerite-related compounds ${\text{Bi}}_{2}{\text{Pd}}_{3}{X}_{2}$ $(X=\text{S,Se})$ were studied. The electrical resistivities of both compounds show typical metallic behavior up to 400 K. Resistivity and specific heat measurements at low temperatures reveal that ${\text{Bi}}_{2}{\text{Pd}}_{3}{\text{Se}}_{2}$ is superconducting below 1 K. On the other hand, ${\text{Bi}}_{2}{\text{Pd}}_{3}{\text{S}}_{2}$ does not show a bulk superconducting transition down to 0.35 K. In the normal state, the electronic specific heat coefficient $\ensuremath{\gamma}$ and the Debye temperature ${\ensuremath{\Theta}}_{\text{D}}$ are found to be $5.9\text{ }\text{mJ}/\text{mol}\text{ }{\text{K}}^{2}$ and 170 K, respectively for ${\text{Bi}}_{2}{\text{Pd}}_{3}{\text{S}}_{2}$, and $8.3\text{ }\text{mJ}/\text{mol}\text{ }{\text{K}}^{2}$ and 150 K, respectively for ${\text{Bi}}_{2}{\text{Pd}}_{3}{\text{Se}}_{2}$. In the superconducting state for ${\text{Bi}}_{2}{\text{Pd}}_{3}{\text{Se}}_{2}$, the upper critical field at zero temperature for ${\text{Bi}}_{2}{\text{Pd}}_{3}{\text{Se}}_{2}$ is 290 mT. From the electronic specific heat in the superconducting temperature range, it was found that ${\text{Bi}}_{2}{\text{Pd}}_{3}{\text{Se}}_{2}$ belongs to an $s$-wave weak-coupling superconductor.