Noisy Kondo impurities

TL;DR

This paper reports on current noise measurements in artificial Kondo impurities within carbon nanotube devices, revealing enhanced noise in the Kondo resonance that challenges simple non-interacting theories and advances understanding of many-body effects out of equilibrium.

Contribution

It introduces noise measurement in artificial Kondo impurities, providing new insights into many-body phenomena in out-of-equilibrium nanoscale systems.

Findings

Enhanced current noise within the Kondo resonance

Contradiction with simple non-interacting theories

Insights into noise properties of molecular devices

Abstract

The anti-ferromagnetic coupling of a magnetic impurity carrying a spin with the conduction electrons spins of a host metal is the basic mechanism responsible for the increase of the resistance of an alloy such as Cu${}_{0.998}$Fe${}_{0.002}$ at low temperature, as originally suggested by Kondo . This coupling has emerged as a very generic property of localized electronic states coupled to a continuum . The possibility to design artificial controllable magnetic impurities in nanoscopic conductors has opened a path to study this many body phenomenon in unusual situations as compared to the initial one and, in particular, in out of equilibrium situations. So far, measurements have focused on the average current. Here, we report on \textit{current fluctuations} (noise) measurements in artificial Kondo impurities made in carbon nanotube devices. We find a striking enhancement of the current noise within the Kondo resonance, in contradiction with simple non-interacting theories. Our findings provide a test bench for one of the most important many-body theories of condensed matter in out of equilibrium situations and shed light on the noise properties of highly conductive molecular devices.