Point-contact spectroscopy of local electron excitations in metals

It is shown that local electron excitations associated with transitions between the levels of the f-shell of rare-earth ions in metals lead to a specific temperature dependence R(T) of the resistance and to the voltage dependence R(V) of the resistance in a point contact between bulky electrodes and rare-earth ions. The second derivative of the I–V characteristic contains two nonlinear contributions, one of which is due to the inelastic scattering of conduction electrons at the f-shell and allows a restoration of the f-level splitting spectrum by the crystalline field. The second nonlinear term appears due to the dependence of the occupation number of excitations on voltage. The regular lattice of rare-earth ions and a disordered solution of rare-earth impurities are considered. At high frequencies, the part of nonlinear conductivity associated with the “population spectroscopy” is separated from the inelastic part of the point-contact spectrum. The relation between R(T) and R(V) for s–f interaction is different from the case of electron–phonon interaction because the local electron excitations do not obey the Bose statistics.