Electrical conductivity of point microbridges and phonon and impurity spectroscopy in normal metals
Annotatsiya
A theory of the nonlinear effects in the electrical conductivity of metallic microbridges is constructed which is based on a model consisting of a hole of radius a in an impermeable partition separating two metallic half-spaces. The electron distribution function, which is a function of the coordinates and which is sharply anisotropic in momentum space, and the electric field distribution in the vicinity of the constriction are found in the limit 1 ⪢ a (where 1 is the electron mean free path). The current–voltage characteristic of the bridge contains nonlinearities induced by inelastic relaxation of electrons on phonons and also on impurities with internal degrees of freedom. The second derivative of the current with respect to voltage is proportional to the constriction spectral function G(ω), which differs from the electron–phonon coupling function normally employed g(ω) by the presence of an additional structure factor K(v,v′) allowing for the geometry of the constriction. At small frequenceis (ω ⪡ ωD) the function G(ω) is proportional to ω4; at frequencies ω ∼ ωD the constriction spectral function G(ω) reflects the singularities of the phonon density of states (including the van Hove singularities). In the case of inelastic scattering of electrons on impurities localized near the hole, the function G(ω) contains peaks corresponding to the discrete impurity excitation levels.