Nonlinear electrical conductivity and spectroscopy of electron–phonon interaction in tunnel point contacts

The theory of nonlinear electrical conductivity for metal point contacts with a barrier layer is constructed. For contacts with a quite small value of the product Dd (D is the transparency of the tunnel barrier and d the diameter of the contact), a mode intermediate between the traditional point-contact spectroscopy mode and tunneling in plane contacts is realized. The concentration of carriers in the contact region produces nonlinear corrections to the I(V) dependence that are similar to those for point contacts but not restricted by the condition of conservation of electron motion through the carrier concentration region. This modification of the point-contact spectroscopy [I. O. Kulik, M. V. Moskalets, R. I. Shekhter, and I. K. Yanson, Pis’ma Zh. Eksp. Teor. Fiz. 49, 42 (1989)] provides a method for investigating the electron–phonon interaction spectrum for materials with extremely small electron mean free paths (fluctuating valency and heavy fermion systems, high-temperature superconductors).

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