New insight into physics of the holes in semiconductors through Terahertz studies in ultra-high magnetic fields

This talk summarizes recent magneto-optical activities at Dresden high magnetic field laboratory. The first part reports a correction to the model potential of the Ga acceptor in germanium, evidenced by high-magnetic-field photoconductivity measurements. It was found that under high magnetic fields the chemical shift of the binding energy of Ga acceptors vanishes, contrary to the results given by the generally accepted theory. To fit our data, we found that the central-cell correction should contain a repulsive part (i.e., it must be bipolar), in contrast to the purely attractive screened point-charge potential widely used in the literature.
In the second part, we report long, ms range, hole spin relaxation time in InGaAs/GaAs quantum wells probed by cyclotron- resonance spectroscopy in pulsed magnetic fields. In our experiments, we found strong hysteresis in the spectral weights of cyclotron resonance absorption lines when rapidly changing magnetic field is used for the experiment. The hysteresis vanishes when a much slower changing magnetic field is used. We attribute this behavior to a long energy relaxation time between two lowest spin-split hole Landau levels, i.e. a long hole spin relaxation time. We also present transition frequencies calculated using a 4x4 Luttinger Hamiltonian, which confirm our findings.