Large spin-orbit effects in small quantum dots

TL;DR

This paper investigates how spin-orbit interactions significantly influence conductance in small quantum dots near many-body energy degeneracies, revealing observable effects at low temperatures and proposing experimental exploration.

Contribution

It demonstrates that spin-orbit effects can dominate conductance behavior near degeneracies in small quantum dots, highlighting conditions for observable phenomena at higher temperatures.

Findings

Spin-orbit effects cause notable conductance changes near degeneracies.

Observable effects persist at temperatures higher than spin-orbit coupling strength.

Results are robust against non-universal perturbations.

Abstract

We consider small ballistic quantum dots weakly coupled to the leads in the chaotic regime and look for significant spin-orbit effects. We find that these effects can become quite prominent in the vicinity of degeneracies of many-body energies. We illustrate the idea by considering a case where the intrinsic exchange term -JS^2 brings singlet and triplet many-body states near each other, while an externally tunable Zeeman term then closes the gap between the singlet and the one of the triplet states (with spin projection parallel the external field). Near this degeneracy, the spin-orbit coupling leads to a striking temperature dependence of the conductance, with observable effects of order unity at temperatures lower than the strength of the spin-orbit coupling. Under favorable circumstances, spelled out in the paper, these order unity effects in the conductance persist to temperatures much higher than the spin-orbit coupling strength. Our conclusions are unaffected by the presence of non-universal perturbations. We suggest a class of experiments to explore this regime.