Enhancing superconductivity of Lu5Rh6Sn18 by atomic disorder

Abstract

For a number of skutterudite-related cage compounds, such as cubic R3M4Sn13 (R=Ca or La, M=transition d-electron metal) or tetragonal Y5Rh6Sn18, we have previously reported the impact of various atomic defects in the crystal lattices on the normal-state and superconducting properties of these clathrates. In these quasiskutterudites the nanoscale disorder and/or local inhomogeneity in composition lead to an abnormal increase in the superconducting transition temperature Tc. Here we investigate the impact of atomic defects in the superconductors Lu5−δRh6Sn18 (tetragonal symmetry I41/acd). We have documented that Lu5Rh6Sn18 does not crystallize in the assumed stoichiometry but forms a 5-6-18 phase with a Lu deficiency (δ≈0.5). Our comprehensive investigations of electronic structure and thermodynamic and electrical transport properties documented a Tc increase in the more disordered sample (sample 1). The quality of two investigated samples (sample 1 and sample 2) with similar stoichiometry but different local inhomogeneity was obtained by microanalysis and electron transmission microscopy observations. The band structure calculations show a hybridization pseudogap in the electronic bands of stoichiometric Lu5Rh6Sn18 at about 0.3 eV in respect to the Fermi level εF. The ab initio calculations predict the scenario that vacancies could shift this pseudogap towards εF, which is manifested by the Mott variable-range hopping behavior in the resistivity ρ∼T−1/4 of more homogeneous sample 2.

Source-reported materials — not catalogue approval

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