On-chip spin control in semiconductor micro- and nano-structures
Gaining spin control is one key issue towards applications of semiconductor spintronic devices. A straightforward way is the usage of an on-chip magnetic field, which allows strongly enhanced spatial resolution and high frequency operation. Here, an approach for demonstrating local spin control and spin manipulation on a micrometer length scale by on-chip microcoils is presented for two specific examples. In a (Cd, Mn)Te/(Cd, Mg)Te diluted magnetic semiconductor quantum well, the electrically switchable magnetic field enables control of the magnetic ion spins. It is found that local spin interactions, i.e. hyperfine interaction, spin coupling with the crystal field and strain-induced electrical field, determine the observed sub-ns Mn2+ spin dynamics in the weak magnetic field regime. At higher magnetic fields, the Zeeman energy exceeds these local interactions and the Mn2+ spin dynamics is controlled by the spin-lattice relaxation process which is typically above the nanosecond timescale. In n-GaAs, the on-chip rf field is applied to control nuclear spins. Optically detected nuclear magnetic resonance (NMR) is demonstrated for the specific isotopes in GaAs. A rf pulse sequence even allows for a coherent control of 75As nuclear spins, manifested by Rabi oscillations with an effective dephasing time of 200 µs. We have been able to observe non-fundamental NMR, giving insight into the elementary processes controlling the nuclear spin dynamics in n-GaAs. By analyzing the nuclear spin depolarization amplitude and the nuclear spin dynamics, it is concluded that the local quadrupole interaction and the current-induced tilted RF field are dominant for the 2 fa and the 1/2 fa NMR, respectively, and the (fa1 + fa2) NMR is related to the nuclear dipole-dipole interaction.