Stokes flow around an obstacle in viscous two-dimensional electron liquid.

The electronic analog of the Poiseuille flow is the transport in a narrow channel with disordered edges that scatter electrons in a diffuse way. In the hydrodynamic regime, the resistivity decreases with temperature, referred to as the Gurzhi effect, distinct from conventional Ohmic behaviour. We studied experimentally an electronic analog of the Stokes flow around a disc immersed in a two-dimensional viscous liquid. The circle obstacle results in an additive contribution to resistivity. If specular boundary conditions apply, it is no longer possible to detect Poiseuille type flow and the Gurzhi effect. However, in flow through a channel with a circular obstacle, the resistivity decreases with temperature. By tuning the temperature, we observed the transport signatures of the ballistic and hydrodynamic regimes on the length scale of disc size. Our experimental results confirm theoretical predictions.

Spectroscopy of systems with time variable parameters: photoreflectance of GaAs(001) under cesium adsorption.

A modification of photoreflectance spectroscopy, which improves the precision and efficiency of measuring time-evolving surface electric fields, is proposed. This modification is explored for studying the band bending evolution under cesium adsorption on the reconstructed GaAs(001) surface and relaxation processes in the non-equilibrium adsorbate overlayer. Observation of several distinct maxima and minima in the coverage dependence of the band bending can be explained by the formation of adatom-induced surface states with a quasi-discrete spectrum.

Anisotropy and molecular rotation in resonant low-energy dissociative recombination.

Angular fragment distributions from the dissociative recombination (DR) of HD(+) were measured with well directed monochromatic low-energy electrons over a dense grid of collision energies from 7 to 35 meV, where pronounced rovibrational Feshbach resonances occur. Significant higher-order anisotropies are found in the distributions, whose size varies along energy in a partial correlation with the relative DR rate from fast-rotating molecules. This may indicate a breakdown of the nonrotation assumption so far applied to predict angular DR fragment distributions.