Superconductivity\nin Single Crystals of Lu₃<i>T</i>₄Ge_{13–<i>x</i>} (<i>T</i> = Co,\nRh, Os) and Y₃<i>T</i>₄Ge_{13–<i>x</i>} (<i>T</i> = Ir, Rh, Os)

Abstract

Single crystals of Lu₃<i>T</i>₄Ge_{13–<i>x</i>} (<i>T</i> = Co,\nRh, Os) and Y₃<i>T</i>₄Ge_{13–<i>x</i>} (<i>T</i> = Ir, Rh, Os) have been grown\nusing the self-flux method and found to adopt the Yb₃Rh₄Sn_{13–<i>x</i>} structure type.\nMagnetization and specific heat measurements confirm that all compounds\nare bulk superconductors, some with reduced superconducting gaps determined\nfrom specific heat suggesting multiband superconductivity. However,\nan unusual increase of the electrical resistivity and a decrease of\nthe charge carrier density on cooling in the normal state are observed\nfor all six compounds even though density functional periodic calculations\nreveal a metallic ground state. We empirically show that large atomic\ndisplacement parameter ratios in the <i>R</i>₃<i>T</i>₄Ge_{13–<i>x</i>} compounds are correlated with the semiconductor-like behavior,\nwhich resolves the contradiction between the experiment and the calculations.