Low Temperature Physics: 41, 595 (2015); https://doi.org/10.1063/1.4929594
Fizika Nizkikh Temperatur: Volume 41, Number 8 (August 2015), p. 768-776    ( to contents , go back )

Inelastic electron–phonon scattering and excess current in superconducting point-contacts with a short coherence length

N.L. Bobrov

B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine 47 Lenin Ave., Kharkov 61103, Ukraine
E-mail: bobrov@ilt.kharkov.ua

Received March 2, 2015, revised April 14, 2015

Abstract

Nonlinear electrical effects in superconducting point S–c–S contacts including the spectroscopy of electron–phonon interaction (EPI) in such systems and recovery of the EPI function from the experimental data are discussed. The influence of magnetic field on I–V curves and their derivatives for the ErNi2B2C point-contacts (PC) with d ≥ ξ (where d is the diameter of PC, ξ is the coherence length) was studied. It is found that at zero magnetic field and in fields close to the critical ones, where the superconducting gap is negligibly small, the position of dV/dI maxima coincide with the position of peaks in the EPI Yanson spectra. A shift of those peaks towards lower energies in small fields and their splitting in intermediate fields were observed. For PCs with d larger or close to ξ the relative value of the negative phonon contribution to the excess current is far larger than for ballistic contacts. It results in a considerable suppression of high-energy peaks in the superconducting state, and a relevant correction is necessary to restore accurately the EPI function. For “dirty” NbSe2 and Nb PCs with d ≥ ξ, that demonstrated no EPI spectra in the second derivative of I–V curves in the normal state these spectra were successfully reconstructed from the data taken in the superconducting state.

PACS: 71.38.–k Polarons and electron–phonon interactions;
PACS: 73.40.Jn Metal-to-metal contacts;
PACS: 74.25.Kc Phonons;
PACS: 74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions;
PACS: 74.50.+r Tunneling phenomena; Josephson effects.

Key words: point-contact spectroscopy, electron–phonon interaction, superconductivity, energy gap, excess current.

Published online: June 23, 2015

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