Symmetry-controlled singlet-triplet transition in a double-barrier quantum ring

TL;DR

This paper demonstrates how a ring-shaped quantum dot system allows electric field control of electron spin states, enabling a switch between singlet and triplet configurations at zero magnetic field, with strong agreement between experiment and theory.

Contribution

The study introduces a novel ring-shaped quantum dot system that enables electric control of spin states and reveals a unique singlet-triplet crossover not seen in traditional quantum dots.

Findings

Electric field switches ground state between singlet and triplet

Excellent match between experimental data and many-body calculations

Ring geometry enables unique singlet-triplet crossover

Abstract

We engineer a system of two strongly confined quantum dots to gain reproducible electrostatic control of the spin at zero magnetic field. Coupling the dots in a tight ring-shaped potential with two tunnel barriers, we demonstrate that an electric field can switch the electron ground state between a singlet and a triplet configuration. Comparing our experimental co-tunneling spectroscopy data to a full many-body treatment of interacting electrons in a double-barrier quantum ring, we find excellent agreement in the evolution of many-body states with electric and magnetic fields. The calculations show that the singlet-triplet energy crossover, not found in conventionally coupled quantum dots, is made possible by the ring-shaped geometry of the confining potential.