Enhancing superconductivity of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Lu</mml:mi><mml:mn>5</mml:mn></mml:msub><mml:msub><mml:mi>Rh</mml:mi><mml:mn>6</mml:mn></mml:msub><mml:msub><mml:mi>Sn</mml:mi><mml:mn>18</mml:mn></mml:msub></mml:mrow></mml:math> by atomic disorder

Abstract

For a number of skutterudite-related cage compounds, such as cubic ${R}_{3}{M}_{4}{\mathrm{Sn}}_{13}$ ($R=\mathrm{Ca}$ or La, $M=\text{transition}$ $d$-electron metal) or tetragonal ${\mathrm{Y}}_{5}{\mathrm{Rh}}_{6}{\mathrm{Sn}}_{18}$, 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 ${T}_{c}$. Here we investigate the impact of atomic defects in the superconductors ${\mathrm{Lu}}_{5\ensuremath{-}\ensuremath{\delta}}{\mathrm{Rh}}_{6}{\mathrm{Sn}}_{18}$ (tetragonal symmetry $I{4}_{1}/acd$). We have documented that ${\mathrm{Lu}}_{5}{\mathrm{Rh}}_{6}{\mathrm{Sn}}_{18}$ does not crystallize in the assumed stoichiometry but forms a 5-6-18 phase with a Lu deficiency ($\ensuremath{\delta}\ensuremath{\approx}0.5$). Our comprehensive investigations of electronic structure and thermodynamic and electrical transport properties documented a ${T}_{c}$ 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 ${\mathrm{Lu}}_{5}{\mathrm{Rh}}_{6}{\mathrm{Sn}}_{18}$ at about 0.3 eV in respect to the Fermi level ${\ensuremath{\epsilon}}_{F}$. The ab initio calculations predict the scenario that vacancies could shift this pseudogap towards ${\ensuremath{\epsilon}}_{F}$, which is manifested by the Mott variable-range hopping behavior in the resistivity $\ensuremath{\rho}\ensuremath{\sim}{T}^{\ensuremath{-}1/4}$ of more homogeneous sample 2.

Topics & Concepts