Nonlinear phenomena in metallic contacts

Abstract

We review and extend theoretical approaches to nonlinear and nonequilibrium effects in metallic microcontacts ranging in their dimension from the atomic to macroscopic sizes. Atomic contacts are shown to quantize their conductance in units of 2e2/h provided the charge redistributes near the constriction to establish the maximal electron transmittivity through the orifice. Ballistic semiclassical contacts are treated both from the Landauer point of view and from the Boltzmann transport theory. The J-V nonlinearity in contacts is related to the inelastic scattering near the narrowest part of the constriction and permits for spectroscopic investigation of phonons in solids (the point-contact spectroscopy).The effects of phonon emission and reabsorption in contacts are taken into consideration. Phonon relaxation is shown to determine the frequency dependence of the nonlinear contact conductivity. Thermal contacts develop specific nonequilibrium states with hot spots in the center of metallic constriction whose temperature is much in excess of the ambient contact temperature and is uniquely related to voltage.