Enhanced superconductivity in hole-doped Nb${}_2$PdS${}_5$

We synthesized a series of Nb${}_2$Pd${}_{1-x}$Ru${}_x$S${}_5$ polycrystalline samples by a solid-state reaction method and systematically investigated the Ru-doping effect on superconductivity by transport and magnetic measurements. It is found that superconductivity is enhanced with Ru doping and is quite robust upon disorder. Hall coefficient measurements indicate that the charge transport is dominated by hole-type charge carriers similar to the case of Ir doping, suggesting multi-band superconductivity. Upon Ru or Ir doping, \emph H${}_{c2}$/${\mathit{\text{T}}}_c$ exhibits a significant enhancement, exceeding the Pauli paramagnetic limit value by a factor of approximately 4. A comparison of $T_c$ and the upper critical field ($H_{c2}$) amongst the different doping elements on Pd site, reveals a significant role of spin–orbit coupling.