Tunable Kondo effect in a single donor atom

TL;DR

This paper reports the observation of a tunable Kondo effect in a single arsenic dopant in silicon, where electric fields control the valley and spin symmetries of the Kondo ground state, enabling reversible symmetry switching.

Contribution

It demonstrates the first electrical control of a valley Kondo effect in a single dopant, revealing a new degree of freedom in Kondo physics.

Findings

Observation of valley Kondo effect in a single dopant.

Reversible switching between SU(2) and SU(4) Kondo states.

Electrical tunability of atomic orbital symmetries.

Abstract

The Kondo effect has been observed in a single gate-tunable atom. The measurement device consists of a single As dopant incorporated in a Silicon nanostructure. The atomic orbitals of the dopant are tunable by the gate electric field. When they are tuned such that the ground state of the atomic system becomes a (nearly) degenerate superposition of two of the Silicon valleys, an exotic and hitherto unobserved valley Kondo effect appears. Together with the regular spin Kondo, the tunable valley Kondo effect allows for reversible electrical control over the symmetry of the Kondo ground state from an SU(2)- to an SU(4) -configuration.