Point-contact spectroscopy ofYbBe13

Abstract

Among rare-earth and actinide ${\mathrm{Be}}_{13}$ intermetallic compounds, ${\mathrm{YbBe}}_{13}$ is anomalous, with evidence for mixed-valence and heavy-fermion behavior. The resistivity is comparatively low and the resulting large mean free path enables point-contact spectroscopy in the ballistic regime. In the ${d}^{2}{V/dI}^{2}$ characteristics of point contacts between ${\mathrm{YbBe}}_{13}$ and normal metals, measured at temperatures between 0.2 and 40 K, we find structures due to crystal-field and Kondo scattering. The characteristics show a pronounced asymmetry, which we explain by the enhanced effective electronic mass in ${\mathrm{YbBe}}_{13}$ and by a shift of the chemical potential in the contact region due to the nonthermal occupation of excited crystal-field levels.