Andreev-reflection spectroscopy of the gap in ZrB12 singlecrystals

摘要

We present the first results of point-contact spectroscopy (PCS) in single crystalsof the boride superconductor ZrB12. The material was first characterized by AC susceptibilityand resistivity measurements, that allowed us to determine the critical temperature, theDebye temperature, the electron-phonon coupling constant and the plasma frequency of thiscompound. Then we performed point-contact measurements that gave conductance curveswith clear Andreev-reflection features typical of a s-wave, single-gap superconductor. Bymeasuring these conductance curves at various temperatures and in the presence of magneticfields, we obtained for the first time the temperature dependence of the gap and of the uppercritical field of ZrB12, as well as an estimate of the Fermi energy. All the results indicate thatZrB12 is a conventional s-wave, weak coupling superconductor.