Thermoelectric effects and the asymmetry of the current-voltage characteristics of metallic point contacts

TL;DR

This paper investigates thermoelectric effects causing asymmetry in current-voltage characteristics of metallic point contacts, proposing a method to determine contact temperature and analyzing effects at different energy ranges.

Contribution

It demonstrates the role of thermoelectric phenomena in contact asymmetry and introduces a technique to measure contact temperature via CVC measurements.

Findings

Asymmetry is caused by thermoelectrical effects like Seebeck, Peltier, and Thompson.

The asymmetry varies with energy range and contact size.

Contact temperature increases linearly with voltage, especially in larger and impurity-rich contacts.

Abstract

An asymmetry as a function of the direction of current flow is observed in the current-voltage characteristic (CVC) and its first and second derivatives for point heterocontacts between pure metals {Cu, Ni, Fe) as well as between these metals and dilute alloys (CuFe, CuMn). It is shown that the observed asymmetry is caused by thermoelectrical phenomena (Seebeck, Peltier, and Thompson effects), observed when the temperature inside the contact differs from the temperature of the bath. In the low energy range (less than or of the order of the Debye energy) the asymmetry of the CVC is affected mainly by the Seebeck effect, while at high energies and for larger contacts (lower resistance) the contributions of all noted effects are of the same order of magnitude. A technique is proposed for determining the temperature of a heterocontact by measuring the CVC in two polarities. It is established that in the intermediate (between the diffusion and ballistic) state of flight of the electrons through the constriction the temperature of the heterocontact increases linearly with the voltage on it, and all the more rapidly the larger the contact and the more impurity in it.