Transient magnetic hybridization of spin and orbital degrees of freedom in two-dimensional quantum rings

Abstract

We consider the effects of interaction of a two-dimensional charged quantum ring with an ultra-short transient perpendicular magnetic field of duration below 10 ps. According to Faraday law, the time variations of magnetic field generate the rotational electric field in the ring, which however, as we show in a paper, can not induce the charge current along the channel of circular ring. It is because the magnetic field preserves the rotational symmetry of the confinement, and thus, can not mix the states of different angular momenta, albeit, the weak radial oscillations of the charge current can be still induced. We show, that the azimuthal component of charge current can be actually generated by an ultra-short magnetic pulse, provided that, the rotational symmetry of the ring is lifted by an in-plane electric field or when a spin-orbit interaction is taken into account. In both cases, the mixing of the angular momentum states is activated by the off-diagonal terms in Hamiltonian matrix. In the latter case, the change of angular momentum of the electron is accompanied by a rotation of its spin, and therefore, depending on an initial polarization of magnetic pulse, the final excitation energy may have a monotonic or an oscillatory character for a longer pulse duration. We conclude that proposed mechanism of fast excitation of charge carriers confined in quantum ring with an ultra-fast magnetic pulse can be applied for an ensemble of self-organized quantum rings, since, these are not usually perfectly circular while the strength of Dresselhaus spin-orbit interaction can be determined in advance, during their fabrication. Additionally, it allows for excitation of charge carriers without heating the sample what takes place if it is irradiated by a laser beam.