Point-contact electron-phonon interaction function in tantalum

TL;DR

This study investigates the electron-phonon interaction in tantalum using point-contact spectroscopy, determining the interaction parameter, spectrum form, and providing improved theoretical models for calculating PC characteristics.

Contribution

The paper accurately determines the EPI function form and parameters in tantalum, compares homocontacts and heterocontacts, and introduces improved theoretical expressions for PC characteristic calculations.

Findings

The contributions of copper and gold in heterocontacts are negligible.

The intensities of Ta-Ta and Ta-Cu spectra are similar.

Proposes using the effective mass approximation over the free-electron approximation.

Abstract

Tantalum is studied by the method of point-contact (PC) spectroscopy: the parameter ${{\lambda }_{pc}}$ and the absolute intensity of the PC EPI function are determined, and the form of the EPI function is determined more accurately. Both homocontacts $Ta-Ta$ and heterocontacts $Ta-Cu$ and $Ta-Au$ were studied. It was found that the contributions of copper and gold to the spectrum of the heterocontact are not noticeable, though the forms of the PC spectra of $Ta$ in homo- and heterocontacts are different. The intensities of the spectra of $Ta-Ta$ homocontacts and $Ta-Cu$ heterocontacts turned out to be close to one another. Simple expressions, enabling numerical calculations of the PC characteristics for geometrically symmetric heterocontacts in the approximation of a spherical Fermi surface, are derived, based on the theory. It is shown that the use of the free-electron approximation in the numerical estimates leads to an error. It is proposed that the effective mass approximation be used for such estimates.