Enhanced upper critical fields in a new quasi-one-dimensional superconductor Nb₂Pd_<i>x</i>Se₅

Abstract

We report a discovery of superconductivity with Tc = 5.5 K in Nb2PdxSe5, in\nwhich one-dimensional (1D) Nb-Se chains existing along the b-direction\nhybridize each other to form the conducting b-c* plane. The magnetic\nsusceptibility and specific heat data in both single- and poly-crystals show\nevidence of bulk superconductivity. The resistivity, Hall coefficient, and\nmagneto-resistance data all indicate the presence of an energy scale T* = ~ 50\nK, which becomes systematically lowered under hydrostatic pressure and competes\nwith the stabilization of superconductivity. Combined with the band calculation\nresults showing the Fermi surfaces with 1D character, we postulate that the\nenergy scale T* is related to a formation of a density wave or a stabilization\nof low dimensional electronic structure. The zero temperature upper critical\nfield, Hc2(0), of the single crystal is found to be 10.5, 35 and 22 T in the\na', b and c*-directions, respectively. While the linearly increasing Hc2(T) for\nH // c* indicates the multi-band effect, Hc2(0) for H // b and c* are found to\nbe much bigger than the BCS Pauli limiting field, 1.84 Tc ~ 9 T. The suppressed\nPauli paramagnetic effect points to a possibility of the enhanced spin-orbit\nscattering related to the low dimensional electronic structure or the presence\nof heavy elements such as Pd.\n