Ferromagnetic Phase in Nonequilibrium Quantum Dots

TL;DR

This paper reveals a robust ferromagnetic phase in nonequilibrium double quantum dots, driven by electron transport and Pauli exclusion, with implications for controlling spin states without magnetic fields.

Contribution

It nonperturbatively solves the nonequilibrium Anderson two-impurity model, discovering a dominant ferromagnetic phase in series-coupled quantum dots under bias.

Findings

Ferromagnetic phase suppresses antiferromagnetic phase at finite bias.

Kondo effects emerge in the ferromagnetic phase at low temperatures.

Stable antiferromagnetic phase persists in weakly correlated limit.

Abstract

By nonperturbatively solving the nonequilibrium Anderson two-impurity model with the hierarchical equations of motion approach, we report a robust ferromagnetic (FM) phase in series-coupled double quantum dots, which can suppress the antiferromagnetic (AFM) phase and dominate the phase diagram at finite bias and detuning energy in the strongly correlated limit. The FM exchange interaction origins from the passive parallel spin arrangement caused by the Pauli exclusion principle during the electrons transport. At very low temperature, the Kondo screening of the magnetic moment in the FM phase induces some nonequilibrium Kondo effects in magnetic susceptibility, spectral functions and current. In the weakly correlated limit, the AFM phase is found still stable, therefore, a magnetic-field-free internal control of spin states can be expected through the continuous FM--AFM phase transition.