Enhanced upper critical fields in a new quasi-one-dimensional superconductor Nb₂Pd_xSe₅

Abstract

We report the discovery of superconductivity with T c = 5.5 K in Nb 2 Pd x Se 5 , in which one-dimensional (1D) Nb-Se chains existing along the b-direction hybridize each other to form the conducting b-c * plane. The magnetic susceptibility and specific heat data in both single crystal and polycrystal show evidence of bulk superconductivity. The resistivity, Hall coefficient and magneto-resistance data all indicate the presence of an energy scale T * = ∼50 K, which becomes systematically lowered under hydrostatic pressure and competes with the stabilization of superconductivity. Combined with the band calculation results showing the Fermi surfaces with 1D character, we postulate that the energy scale T * is related to the formation of a density wave 5

Single gap s-wave superconductivity in Nb2PdS5

“…This value exceeds the Pauli paramagnetic limit Hc 2 (0) = 1.84T c by over 3 times [1][2][3][4]. The anisotropic upper critical field ( ~ 3) along with temperature dependent anisotropy was indicative of possible multiband superconductivity [1,5]. Concepts related to strong spin-orbit scattering and spin triplet pairing mechanism were invoked to explain the highest ever reported H c2 (0)/T c value [4,5].…”

“…The band structure calculations show that the Fermi surface of Nb 2 PdS 5 is composed of multiple sheets with both quasi-two-dimensional (Q2D) hole character and quasi-onedimensional (Q1D) sheets of both hole and electron character that may give rise to multiband superconductivity [1,5]. Multiband superconductivity is also predicted for similar quasi onedimensional isomorphic Nb 2 Pd x Se 5 and Ta 2 Pd x S 5 compounds [9,10].…”

Unconventional Andreev reflection on the quasi-one-dimensional superconductor Nb2PdxSe5

“…6 To be consistent with Ref. 6, where synthesis of the crystals is discussed, we define a' and c* directions as [-2 0 1] and [1 0 2], respectively.…”

“…11 Single crystals of these chalcogenide superconductors are all needle-like with a preferred growth direction along the b-axis of the monoclinic crystal structure. Theoretical calculations on some Q1D chalcogenide superconductors 6,10 have suggested that the Fermi surface in the normal state of the materials is strongly anisotropic and consists of multiple bands. In the superconducting state, chalcogenide superconductors are all found to have an extremely large upper critical field (H C2 ), which is strongly anisotropic and well above the BCS Pauli limit 6-11 similar to Q1D organic superconductors.…”

“…6 or chemical vapor transport (CVT). For CVT, powder of polycrystalline Nb 2 Pd x Se 5 was mixed with an appropriate amount of SeCl 4 as a transport agent and sealed in an evacuated quartz tube.…”