Enhanced Upper Critical Fields in a New Quasi-one-dimensional Superconductor Nb$_2$Pd$_{x}$Se$_5$

We report a discovery of superconductivity with $T_{\mathrm{c}} =$ 5.5 K in Nb$_2$Pd$_{x}$Se$_5$ in which one-dimensional (1D) Nb-Se chains exist along the $b$-direction and each conducting chain is hybridized to form the conducting \textit{bc}* planes. Magnetic susceptibility and heat capacity data in both single- and poly-crystals constitute evidences of bulk superconductivity and BCS-type pairing mechanism. The zero temperature upper critical fields, $H_{\mathrm{c2}}$(0), of a single crystal are found to be 10.5, 35 and 22 T for $a$', $b$ and $c$* directions respectively. $H_{\mathrm{c2}}$(0) is clearly much larger than the expected Pauli limiting field 1.84$T_{\mathrm{c}} \approx $ 9 T along the $b$ and $c$*-direction. We will discuss the possible explanations of such enhancement of $H_{\mathrm{c2}}$ via suppression the Pauli limiting effect, based on the large spin-orbit scattering and the quasi-1D nature of electronic structure in analogy to an organic superconductor (TMTSF)$_{2}X$ ($X =$ PF$_6$, ClO$_4)$ and a purple bronze Li$_{0.9}$Mo$_6$O$_{17}$.