Condensed Matter Theory

Abstract:

We present a lattice Boltzmann algorithm which can be used to explore the spreading of droplets on chemically and topologically patterned substrates. As an example we use the method to show that the final configuration of a drop on a substrate comprising hydrophobic and hydrophilic stripes can depend sensitively on the dynamical pathway by which the state is reached. We also consider a substrate covered with micron-scale posts and investigate how this can lead to superhydrophobic behaviour. Finally we model how a Namibian desert beetle collects water from the wind. © Indian Academy of Sciences.

Abstract:

We show both experimentally and theoretically that the recently observed optically induced in-plane charge separation in quantum well (QW) structures and the exciton ring emission pattern at this charge separation boundary have an extremely long lifetime. The oppositely charged carriers remain separated and provide a reservoir of excitons at their boundary with a persistent emission which lasts hundreds of microseconds (orders of magnitude longer than their recombination time) after the external excitation is removed. This long lifetime is due to an interplay between the slow in-plane carrier diffusion and slow carrier tunneling perpendicular to the QW plane. ©2005 The American Physical Society.

Abstract:

In a fluctuating medium of quantum, thermal, or non-thermal origin, an interaction is induced between external objects that modify the fluctuations. These interactions can appear in a vast variety of systems, leading to a plethora of interesting phenomena. Notable examples of these include: (1) like-charge attraction in the presence of multivalent counterions, (2) Ludwig-Soret effect in charged colloids, (3) mass renormalization of moving defects in a phononic background and moving metallic objects in EM quantum vacuum, and (4) dissipation due to motion-induced radiation. The fluctuation-induced forces are statistical in nature, and this could make their measurement very difficult, because the actual value of the force might deviate most of the time from the predicted average value. © Indian Academy of Sciences.

Abstract:

In Quantum Hall bilayers, at total filling factor one, a transition from a compressible phase with weak interlayer correlations to an incompressible phase with strong interlayer correlations is observed as the distance between the two layers is reduced. The transition between these two regimes can be understood using a trial wavefunction approach based on the composite particle picture. © EDP Sciences.

Abstract:

The analysis of network models - either directly or by numerical studies of related quantum spin chains with super group symmetry - allows to gain insights into the delocalization transition of non-interacting two-dimensional electrons with disorder. Critical exponents determined this way are an important step towards the identification of the conformal field theory (CFT) describing the universal physics at the transition. To collect more information on the universal properties integrable versions of the corresponding superspin chains have been proposed. A simplified version avoiding some of the technical problems of the original problem is the sl(2|l) superspin chain related to the so-called spin quantum Hall transition. Analyzing the ground state and some low-lying excitations of this integrable chain we determine the central charge of the underlying CFT and obtain evidence for an infinite degeneracy of the finite size gaps that are possibly related to a continuous spectrum of the CFT. Finally, we compare our findings for the integrable chain with known properties of the (non-integrable) network model for the spin QHE. © Springer-Verlag Berlin Heidelberg 2005.