Nonequilibrium current-carrying states in metallic point contacts
Abstract
Nonequilibrium phenomena in the electron-phonon system of a normal metal in the current-carrying state under the conditions of strong current concentration are studied. It is shown that for a short phonon momentum mean-free path length lr < d in a point contact with diameter d which is small compared with the phonon and electron energy relaxation lengths lph and le, a nonequilibrium phonon distribution differing from a Planck distribution with an effective temperature of Θ∼eV/4 is established. This gives rise to “nonspectral” corrections to the current-voltage characteristic (the so-called background in point-contact spectra) and to a substantial frequency dispersion of the nonlinear conductivity of the point contact in the region of relatively low frequencies ω ∼ νph∼λ (s/υF) ωD ∼ 1010–1011 sec−1. Study of the latter enables not only determining with the help of point-contact spectroscopy the electron-phonon interaction function g(ω) = α2F(ω), but it also enables obtaining direct information on relaxation rates of Debye phonons in the metal. The background formed by nonequilibrium phonons in point-contact spectra is absent at frequencies ω ≫ νph.