Observation of the two-channel Kondo effect

TL;DR

This paper reports the experimental observation of the two-channel Kondo effect in a nano-engineered semiconductor system, demonstrating a quantum phase transition to an exotic entangled electron state.

Contribution

It presents the first realization and in situ tuning of the two-channel Kondo state in a semiconductor nanostructure, revealing a quantum critical point.

Findings

Observation of the two-channel Kondo effect

Tuning through a quantum phase transition

Identification of a quantum critical point

Abstract

Some of the most intriguing problems in solid state physics arise when the motion of one electron dramatically affects the motion of surrounding electrons. Traditionally, such highly-correlated electron systems have been studied mainly in materials with complex transition metal chemistry. Over the past decade, researchers have learned to confine one or a few electrons within a nanoscale semiconductor "artificial atom", and to understand and control this simple system in exquisite detail. In this Article, we combine such individually well-understood components to create a novel highly-correlated electron system within a nano-engineered semiconductor structure. We tune the system in situ through a quantum phase transition between two distinct states, one familiar and one subtly new. The boundary between these states is a quantum critical point: the exotic and previously elusive two-channel Kondo state, in which electrons in two reservoirs are entangled through their interaction with a single localized spin.