Low temperature resistance minimum in non-superconducting 3R-Nb_{1+x}S_2 and 3R-Ga_xNbS_2

Abstract

We report the structural and electron transport properties of 3R-Nb_{1+x}S_2 (x >= .07) and 3R-Ga_xNbS_2 (.1 <= x <= .33) prepared as polycrystalline pellets as well as single crystals grown by vapour transport. We observe a resistance minimum in these compounds between 20-60 K, with the T_min proportional to x. The resistance scales as rho/rho_min(T/T_min) between .2 < T/T_min < 2 for different phases with x <= .25 whose resistivity differs by an order of magnitude. Powder X-ray diffraction (XRD) also shows progressively increasing intensity of superlattice lines with cation concentration. The thermopower changes sign around the resistance minimum. The explanation of the resistance minimum and the simultaneous rapid suppression of superconductivity is sought in e-e scattering effects in the presence of cation disorder in these narrow band anisotropic materials.

13 pages, 6 figures, to be published in J. Phys.: Condensed Matter

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