Rolf R. Gerhardts

Self-consistent local equilibrium model for density profile and distribution of dissipative currents in a Hall bar under strong magnetic fields

Recent spatially resolved measurements of the electrostatic-potential variation across a Hall bar in strong magnetic fields, which revealed a clear correlation between current-carrying strips and incompressible strips expected near the edges of the Hall bar, cannot be understood on the basis of existing equilibrium theories. To explain these experiments, we generalize the Thomas-Fermi-Poisson approach for the self-consistent calculation of electrostatic potential and electron density in total thermal equilibrium to a local equilibrium theory that allows us to treat finite gradients of the electrochemical potential as driving forces of currents in the presence of dissipation. A conventional conductivity model with small values of the longitudinal conductivity for integer values of the (local) Landau-level filling factor shows that, in apparent agreement with experiment, the current density is localized near incompressible strips, whose location and width in turn depend on the applied current.

High field magnetoresistance at low temperatures

To explain recent experiments on n-InSb we calculate the transverse and longitudinal electrical conductivity in strong magnetic fields. We consider a free electron-point impurity system in the generalized Born approximation, and in the self-consistentt-matrix approximation. The position, shape and amplitude of the Shubnikovde Haas oscillations and the quantum limit behaviour are in good agreement with experiment.

Theory of quantum dot helium

Abstract The competition between the Coulomb interaction and the binding forces due to the confinement and the magnetic field induces transitions of the ground state of quantum dots with few electrons. We demonstrate that for quantum dot helium these transitions occur between states with differently strong correlations between the electrons. By the response of quantum dot helium to far infrared radiation we exemplify that a proper treatment of the correlation effects may be essential for a correct interpretation of experimental data on quantum dots with few electrons.

The Auger-effect in Hg1−xCdxTe

Abstract The temperature dependence of the Auger-lifetime of n-Hg1−xCdxTe is investigated both theoretically and experimentally for several values of bandgap and of extrinsic carrier-concentration nex in the whole range between room and He-temperatures. For semiconducting compounds a pronounced minimum of the lifetime between 10 and 50K and an exponential increase at still lower temperatures are found. The position of the minimum and the exponent depend mainly on the value of the bandgap and on the ratio of the conduction- and valenceband effective masses. Apart from the extended temperature range, which does not allow the use of classical statistics, our calculation differs from earlier work in so far, as we take the band energies and the overlap integrals of conduction- and valenceband Bloch-functions from a k·p-calculation. For semiconducting compounds, we compare the results with those obtained from an estimate of the overlap integrals given by Antoncik and Landsberg. Whereas both results are compatible at high temperatures, characteristic differences occur at low temperatures, where we find the lifetime to be proportional to n ex −8 3 rather than to nex−2. For semimetallic compounds we calculate a weakly temperature dependent Auger-time of the order of 0.1–1 nsec.

Magnetoresistance of a two-dimensional electron gas with spatially periodic lateral modulations: Exact consequences of Boltzmann’s equation

On the basis of Boltzmanns equation, including anisotropic scattering in the collision operator, we investigate the effect of one-dimensional superlattices on two-dimensional electron systems. In addition to superlattices defined by static electric and magnetic fields, we consider mobility superlattices describing a spatially modulated density of scattering centers. We prove that magnetic and electric superlattices in the

Cumulant approach to the two-dimensional magneto-conductivity problem

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Path-integral approach to the two-dimensional magneto-conductivity problem

direction affect only the resistivity component

Thomas-Fermi-Poisson theory of screening for laterally confined and unconfined two-dimensional electron systems in strong magnetic fields

{\ensuremath{\rho}}_{\mathrm{xx}}

Magnetoresistance oscillations induced by periodically arranged micromagnets (invited)

if the mobility is homogeneous, whereas a mobility lattice in the

Cyclotron masses of asymmetrically doped HgTe quantum wells

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