Two-channel Kondo effect and renormalization flow with macroscopic quantum charge states

TL;DR

This paper demonstrates the charge Kondo effect in a hybrid metal-semiconductor single-electron transistor, revealing the renormalization flow of two competing Kondo channels and providing insights into multi-channel Kondo physics and quantum criticality.

Contribution

It experimentally realizes the charge Kondo effect with tunable two-channel Kondo physics in a single-electron transistor, enabling direct observation of renormalization flow and quantum phase transition.

Findings

Observation of the charge Kondo effect in a hybrid device

Visualization of the renormalization flow of two Kondo channels

Quantitative agreement with finite-temperature crossover predictions

Abstract

Many-body correlations and macroscopic quantum behaviors are fascinating condensed matter problems. A powerful test-bed for the many-body concepts and methods is the Kondo model which entails the coupling of a quantum impurity to a continuum of states. It is central in highly correlated systems and can be explored with tunable nanostructures. Although Kondo physics is usually associated with the hybridization of itinerant electrons with microscopic magnetic moments, theory predicts that it can arise whenever degenerate quantum states are coupled to a continuum. Here we demonstrate the previously elusive `charge' Kondo effect in a hybrid metal-semiconductor implementation of a single-electron transistor, with a quantum pseudospin-1/2 constituted by two degenerate macroscopic charge states of a metallic island. In contrast to other Kondo nanostructures, each conduction channel connecting the island to an electrode constitutes a distinct and fully tunable Kondo channel, thereby providing an unprecedented access to the two-channel Kondo effect and a clear path to multi-channel Kondo physics. Using a weakly coupled probe, we reveal the renormalization flow, as temperature is reduced, of two Kondo channels competing to screen the charge pseudospin. This provides a direct view of how the predicted quantum phase transition develops across the symmetric quantum critical point. Detuning the pseudospin away from degeneracy, we demonstrate, on a fully characterized device, quantitative agreement with the predictions for the finite-temperature crossover from quantum criticality.