Magnetic field controlled topological transitions of the spin field in quantum rings with spin orbit couplings

The spin fields of the ground state of the two-dimensional quantum rings with Rashba and Dresselhaus spin-orbit couplings are studied and compared with our analysis of the one-dimensional model. The topological charge of the spin field varies periodically due to the step-like change of the angular momentum with an increase of the magnetic field which is perpendicular to the ring. We also demonstrate the cases where the one-dimensional model is invalid or unreliable for a relatively wide ring, by comparing with the reliable numerical results of the two-dimensional model. As a result, the period of the topological transition can be biased from the period of the Aharonov-Bohm effect. Moreover, in a non-symmetric quantum ring where a non-magnetic impurity is located, the density and the spin textures of the single-electron ground state jointly make a dramatic change comparing with the one-dimensional model. Even higher topological charge ±2 of the spin field at single-electron level can be achieved by tuning the magnetic field, which indicates a great advantage over other systems in potential applications. © 2020 Elsevier B.V.