Anne Beate Hummel

The coherent Hall effect of charge carriers in a superlattice: semiclassical description of the wavepacket dynamics

The coherent Hall effect of charge carriers is the quantum mechanical analogue of the classical Hall effect for the case where the charge carriers are a coherent ensemble of wavepackets. Kosevich considered this effect for the first time for semiconductor superlattices subjected both to an electric field along the growth direction and to a perpendicular magnetic field (Kosevich Y A 1999 Ann.?Phys.?8 SI-145; 2001 Phys.?Rev.?B?63 205313). The dynamics of the charge carriers can be described successfully by means of a semiclassical model mapping the equation of motion to a simple pendulum equation with the deflection angle in the case of the pendulum being replaced by the k-vector of the wavepackets along the superlattices growth direction. While Kosevich has presented an analytical treatment of the equation of motion, we numerically solve it and compute the real-space and k-space trajectories of the charge carriers. We thus arrive at a more illustrative and detailed analysis of the wavepacket dynamics and make predictions for optical pump?probe experiments which detect either the terahertz radiation emitted by the oscillating charge carriers or the internal electric field as a function of time after impulsive excitation of charge carriers.

Mirrors and output couplers for THz and optical radiation

Summary form only given. We use time-resolved THz spectroscopy in order to investigate the properties of highly conductive thin films. In this contribution we present experimental data on two of such film systems, which can be used in free-space THz radiation applications. We perform experiments on a thin indium tin oxide (ITO) film evaporated on a highly insulating glass substrate, in order to investigate its properties as a dichroic beamsplitter for THz and optical frequencies. In addition we study three different samples consisting of epitaxially grown p/sup +/-doped GaAs layers on GaAs substrates with different doping concentrations and layer thicknesses which are commonly used as contact layers in semiconductor devices (e.g. THz emitter structures).

Evolution of energy levels of a GaAs/AlGaAs superlattice under the influence of a strong magnetic field

We present photocurrent spectra of the Wannier–Stark ladder of a GaAs/AlGaAs superlattice in a magnetic field up to 9 T and oriented along the growth direction of the superlattice. The Landau and Wannier–Stark quantization directions are perpendicular to each other. The salient observation is the evolution of Landau fans for the different Wannier–Stark transitions, with the Landau fan assigned to the spatially direct Wannier–Stark-ladder transitions being very pronounced quite in contrast to the Landau fans for the spatially indirect Wannier–Stark transitions which are weak.