Jose A. Brum

Optically controlled spin-polarization memory effect on Mn delta-doped heterostructures

We investigated the dynamics of the interaction between spin-polarized photo-created carriers and Mn ions on InGaAs/GaAs: Mn structures. The carriers are confined in an InGaAs quantum well and the Mn ions come from a Mn delta-layer grown at the GaAs barrier close to the well. Even though the carriers and the Mn ions are spatially separated, the interaction between them is demonstrated by time-resolved spin-polarized photoluminescence measurements. Using a pre-pulse laser excitation with an opposite circular-polarization clearly reduces the polarization degree of the quantum-well emission for samples where a strong magnetic interaction is observed. The results demonstrate that the Mn ions act as a spin-memory that can be optically controlled by the polarization of the photocreated carriers. On the other hand, the spin-polarized Mn ions also affect the spin-polarization of the subsequently created carriers as observed by their spin relaxation time. These effects fade away with increasing time delays between the pulses as well as with increasing temperatures.

Magneto-excitons in droplets of a chiral Luttinger liquid formed in quantum dots in a magnetic field

Magneto-excitons in droplets of a spin polarized chiral Luttinger liquid formed in quantum dots in a magnetic field are studied. The coupling of magneto-excitons to low energy excitations of an interacting droplet (edge magneto-rotons) leads to a strong enhancement of the oscillator strength at the Fermi level (Fermi edge singularity). The condensation of edge magneto-rotons signals the reconstruction of the droplet and is accompanied by new structures in the absorption spectrum.

Electronic structure of holes in modulation doped p-Si1-xGex/Si strained quantum wells in a magnetic field

Abstract The results of self-consistent calculations of hole energy levels in strained, symmetric and asymmetric, p -type modulation doped Si 1−x Ge x /Si quantum wells in a magnetic field are reported. The band mixing is responsible for the enhanced effective g -factor of the opposite parity states. This leads to gaps at predominantly odd filling factors. The calculated filling factor dependent energy gaps are compared with gaps obtained from magneto-transport measurements.