Point-contact spectroscopy of local electronic excitations in metals

Local electric excitations, i. e. transitions between crystal-electric-field splitted f-level of the rare-earth (or actinide) ion results in the specific temperature dependence of the resistance, R(T) as well as voltage dependence of the resistance R(V) in point contact connecting bulk metallic electrodes with RE contamination. The second derivative of current-voltage characteristic reveals two nonlinear contributions one of which is related to the inelastic scattering of conductance electrons on the f-shell and permits to probe CEF splitted levels of the ion, while the other results from the energy dependence of the population of CEF states. Two limiting cases of regular lattice of RE ions, as well as the irregular array of ''RE impurities'', are considered. By measuring the high-frequency conductivity of the point contact, one may separate the nonlinear part of conductivity corresponding to the intrinsic, i.e. inelastic point-contact spectroscopy of CEF states. Relation between R(T) and R(V) dependences in point contact with RE ions differs from that in case of elecon-phonon interaction, due to non-Bose statistics of the local electron excitation