17. Band Mixing Effects in InAs/GaAs Quantum Rings and in MoS\(_2\) Quantum Dots Ring-Like Behaving

The physics of semiconductor quantum rings near the band edge is often well described considering decoupled bands. There are however instances where band coupling leads to relevant changes in the electronic structure and derived properties. In this chapter we analyze two such cases. First, we focus on the heavy hole-light hole band mixing in self-assembled InAs/GaAs quantum rings, which is important for current endeavour to develop quantum information science using the spin of holes. In InAs/GaAs quantum dots, the hole ground state is known to be mainly formed by the heavy hole subband. However, there is a finite spin-orbit coupling with the light-hole subband which is critical in determining the hole spin properties. Based on k\(\cdot \)p theory, in this chapter we study the influence of hole subband mixing in quantum rings. It is shown that the inner cavity of the ring enhances the light hole component of the ground state. As the quasi-1D limit is approached, the light-hole character becomes comparable to that of the heavy hole. Strain reduces the coupling, but it is still larger than in quantum dots. Second, we study the electronic structure of monolayer MoS\(_2\) quantum dots subject to a magnetic field. Here, the coupling between conduction and valence band gives rise to mid-gap topological states which localize near the dot edge. These edge states are analogous to those of 1D quantum rings. We show they present a large, Zeeman-like, linear splitting with the magnetic field, anticross with the delocalized Fock-Darwin-like states of the dot, give rise to Aharonov-Bohm-like oscillations of the conduction (valence) band low-lying states in the K (K\(^{\prime }\)) valley, and modify the strong-field Landau levels limit form of the energy spectrum.