Anomalous metallic state and anisotropic multiband superconductivity in Nb3Pd0.7Se7

Abstract

We report the discovery of superconductivity in Nb3PdxSe7 with a x-dependent superconducting transition-temperature as high as Tc ≃ 2.1 K for x ≃ 0.7 (middle point of the resistive transition). Needle-like single crystals display anisotropic upper-critical fields with an anisotropy γ = H b c2 /H a c2 as large as 6 between fields applied along their needle axis (or b−axis) or along the a−axis. As for the Fe based superconductors γ is temperature-dependent suggesting that Nb3Pd0.7Se7 is a multi-band superconductor. This is supported by band structure calculations which reveal a Fermi surface composed of quasi-one-dimensional and quasi-two-dimensional sheets of hole character, as well as three-dimensional sheets of both hole-and electron-character. Remarkably, H b c2 is observed to saturate at H b c2 (T → 0K) ≃ 14.1 T which is 4.26 × Hp where Hp is the Pauli-limiting field in the weak-coupling regime. The synthesis procedure yields additional crystals belonging to the Nb2PdxSe5 phase which also becomes superconducting when the fraction of Pd is varied. For both phases we find that superconductivity condenses out of an anomalous metallic state, i.e. displaying ∂ρ/∂T < 0 above Tc similarly to what is observed in the pseudogap-phase of the underdoped cuprates. An anomalous metallic state, low-dimensionality, multi-band character, extremely high and anisotropic Hc2s, are all ingredients for unconventional superconductivity.

Multiband superconductivity ofTa4Pd3Te16from Tepstates

“…The structure differs from those of the superconducting chalcogenides Ta 2 PdS 5 , Nb 2 Pd 0.8 S 5 and Nb 3 Pd 0.7 Se 7 in being a stoichiometric compound with nominally flat two dimensional sheets in the crystal structure. [3][4][5][6] We note that there is the possibility that the layered crystal structure may be misleading from the point of view of the electronic properties, as previous electronic structure calculations by Alemany and co-workers showed important interlayer Te -Te interactions.…”

Superconducting Fiber with Transition Temperature up to 7.43 K in Nb2PdxS5−δ (0.6 < x <1)

“…For practical uses, it is very important that a superconducting material is flexible. [4][5][6][7][8][9][10][11] Despite of the relatively lower superconducting transition temperature (less than 10 K), their discovery attracts much attention due to their potential application perspectives and scientific importance. Here we report the growth and the characterization of Nb 2 Pd x S 5- (0.6<x<1) superconducting fibers by using traditional flux-melting method.…”

Controllable spin-orbit coupling and its influence on the upper critical field in the chemically doped quasi-one-dimensionalNb2PdS5superconductor

“…Recently, a new ternary compound Nb 2 PdS 5 with onedimensional Pd chains has been reported to be superconducting below T c ∼ 6 K. [14][15][16][17][18][19][20] Remarkably, its upper critical magnetic field H c2 along the chains was observed to exceed the Pauli paramagnetic limit by a factor of 3.…”