Electronic states in semiconductor double quantum dots and quantum rings - Theory and tight-binding modeling

Sammanfattning: In recent experiments on semiconductor nanowires and quantum dots, enhanced g-factors up to several times the bulk value have been measured [1] [2]. The enhancement is attributed to orbital contributions g∗orb to the effective g-factor g∗ = g∗spin+g∗orb from the coupling of the high angular momentum ring-like states to the magnetic field. The objective of the work presented here is to model the double quantum dot (DQD) system in [1], extending previous theoretical models to a two-dimensional (2D) tightbinding ring-shaped structure using the open-source python package Kwant [3]. It is found that the enhanced g-factors can be straightforwardly predicted by the model because of the formation of ring-like states when an even orbital on one dot aligns with an odd orbital in the other dot. Ring states require combinations of even and odd orbitals at zero magnetic field, even-even (similarly odd-odd) orbital parity combinations lead to poor ring formation. Moreover, Aharonov-Bohm oscillations are also present in the model when the ring is penetrated by a significant flux in agreement with recent experimental findings in similar systems. The states of interest transforms from crossing to anti-crossing when increasing the flux through the ring from 0 to 1/2 flux quanta as the parity requirement of the aligned orbitals to form ring states are reversed. This means at 1/2 flux quanta the condition of even-odd orbital alignment to form good ring states is broken and even-even and odd-odd orbital combinations form good ring states instead. The model presented here is a more realistic description of the real experimental system compared with previous theory and the results are consistent with experimental findings.