Electronic states in a magnetic quantum-dot molecule: phase transitions and spontaneous symmetry breaking

TL;DR

This paper investigates how magnetic quantum-dot molecules exhibit phase transitions and spontaneous symmetry breaking, revealing unique ground states due to magnetic interactions that differ from non-magnetic molecules.

Contribution

It introduces the concept of symmetry-breaking ground states in magnetic quantum-dot molecules caused by the interplay of tunnelling and magnetic polaron energies.

Findings

Ground state transitions from symmetric to broken symmetry with temperature decrease

Broken-symmetry phases can be controlled via voltage for memory applications

Symmetry is recovered at very low temperatures in magnetic molecules

Abstract

We show that a double quantum-dot system made of diluted magnetic semiconductor behaves unlike usual molecules. In a semiconductor double quantum dot or in a diatomic molecule, the ground state of a single carrier is described by a symmetric orbital. In a magnetic material molecule, new ground states with broken symmetry can appear due the competition between the tunnelling and magnetic polaron energy. With decreasing temperature, the ground state changes from the normal symmetric state to a state with spontaneously broken symmetry. Interestingly, the symmetry of a magnetic molecule is recovered at very low temperatures. A magnetic double quantum dot with broken-symmetry phases can be used a voltage-controlled nanoscale memory cell.