Signature of Fermi surface anisotropy in point contact conductance in the presence of defects

TL;DR

This paper explores how Fermi surface anisotropy influences conductance oscillations in scanning tunneling microscopy, revealing that the Fermi surface shape affects defect imaging accuracy.

Contribution

It extends previous work by analyzing the impact of Fermi surface anisotropy on conductance oscillations, providing conditions for improved defect detection.

Findings

Conductance oscillation amplitude and period depend on Fermi surface geometry.

Maximum conductance oscillation amplitude may not occur directly above the defect.

Optimal conditions for defect imaging vary with Fermi surface type.

Abstract

In a previous paper (Avotina et al.,Phys. Rev. B Vol.71, 115430 (2005)) we have shown that in principle it is possible to image the defect positions below a metal surface by means of a scanning tunnelling microscope. The principle relies on the interference of electron waves scattered on the defects, which give rise to small but measurable conductance fluctuations. Whereas in that work the band structure was assumed to be free-electron like, here we investigate the effects of Fermi surface anisotropy. We demonstrate that the amplitude and period of the conductance oscillations are determined by the local geometry of the Fermi surface. The signal results from those points for which the electron velocity is directed along the vector connecting the point contact to the defect. For a general Fermi surface geometry the position of the maximum amplitude of the conductance oscillations is not found for the tip directly above the defect. We have determined optimal conditions for determination of defect positions in metals with closed and open Fermi surfaces.