Electron coherence at low temperatures: The role of magnetic impurities

TL;DR

This paper reviews recent experimental findings on electron phase coherence in metallic quantum wires, emphasizing how magnetic impurities influence the saturation of coherence time at low temperatures, supported by new ultra-clean gold and silver wire measurements.

Contribution

It provides new measurements of phase coherence times in ultra-clean gold and silver wires and analyzes the impact of magnetic impurities on coherence saturation.

Findings

Magnetic impurities cause saturation of phase coherence time at low temperatures.

Ultra-clean samples show saturation consistent with extremely low magnetic impurity levels.

Kondo temperatures below 1 mK are relevant for observed saturation phenomena.

Abstract

We review recent experimental progress on the saturation problem in metallic quantum wires. In particular, we address the influence of magnetic impurities on the electron phase coherence time. We also present new measurements of the phase coherence time in ultra-clean gold and silver wires and analyse the saturation of \tauphi in these samples, cognizant of the role of magnetic scattering. For the cleanest samples, Kondo temperatures below 1 mK and extremely-small magnetic-impurity concentration levels of less than 0.08 ppm have to be assumed to attribute the observed saturation to the presence of magnetic impurities.