Nonlinear electric conductivity of point contacts in the multiphonon generation regime

The electron-phonon relaxation of the transport current in point contacts of conductors with a large value of the parameter eV/εF is studied theoretically (here, eV is the bias voltage at the contact, and εf is the Fermi energy of the current carriers). It is shown that under the condition d, li, ≪ ε = (lilε)1/2, where d is the contact size and li, lε are the mean free paths for the elastic and inelastic scattering of electrons respectively, the poin-tcontact (PC) spectrum of the electron–phonon interaction is determined by the inelastic relaxation of electrons at distances r ∼ λε from the point contact. The resulting successive emission of several phonons is responsible for the experimentally observed repetition of the PC spectrum singularities at multiple frequencies and combination phonon frequencies (multiphonon PC spectrum). The amplitudes of the singularities slowly decrease with the multiplicity number and increase with the contamination of the conductor. Peculiarities of the multiphonon generation in point contacts with a weak screening of the electric field are also considered.

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