Microcontact phonon spectroscopy in the dirty limit

Second voltage derivatives of the current through metallic microcontacts with short (or medium) electron mean free path li as compared with the hole diameter d are investigated. Despite the considerable background present (the smooth dependence of d2I/dV2 on V), the position of the main features of the microcontact spectra on the energy axis remains the same as in pure contacts. This facilitates the use of microcontact spectroscopy as a tool for the study of disordered systems, such as alloys, amorphous films, and heavily deformed materials. Calculations show that the electron–phonon scattering structure factor K(p, p′) depends on the ratio li/d and does not lead to the formation of a background. The latter is due to the nonequilibrium in the phonon system for large contact radii, i.e., high injection currents.

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