Hyperfine interaction induced critical exponents in the quantum Hall effect

We study localization-delocalization transition in quantum Hall systems with a random field of nuclear spins acting on two-dimensional (2d) electron spins via hyperfine contact (Fermi) interaction. We use Chalker-Coddington network model, which corresponds to the projection onto the lowest Landau level. The inhomogeneous nuclear polarization acts on the electrons as an additional confining potential, and, therefore, introduces additional parameter $p$ (the probability to find a polarized nucleus in the vicinity of a saddle point of random potential) responsible for the change from quantum to classical behavior. In this manner we obtain two critical exponents corresponding to quantum and classical percolation. We also study how the 2d extended state develops into the one-dimensional (1d) critical state.Comment: 9 pages, 3 figure

Isotopically engineered silicon/silicon-germanium nanostructures as basic elements for a nuclear spin quantum computer

The idea of quantum computation is the most promising recent developments in the high-tech domain, while experimental realization of a quantum computer poses a formidable challenge. Among the proposed models especially attractive are semiconductor based nuclear spin quantum computer's (S-NSQC), where nuclear spins are used as quantum bistable elements, ''qubits'', coupled to the electron spin and orbital dynamics. We propose here a scheme for implementation of basic elements for S-NSQC's which are realizable within achievements of the modern nanotechnology. These elements are expected to be based on a nuclear-spin-controlled isotopically engineered Si/SiGe heterojunction, because in these semiconductors one can vary the abundance of nuclear spins by engineering the isotopic composition. A specific device is suggested, which allows one to model the processes of recording, reading and information transfer on a quantum level using the technique of electrical detection of the magnetic state of nuclear spins. Improvement of this technique for a semiconductor system with a relatively small number of nuclei might be applied to the manipulation of nuclear spin ''qubits'' in the future S-NSQC.Comment: 11 pages, 2 figures, PostScript, GS vie

Spin-engineered quantum dots

Spatially nonhomogeneously spin polarized nuclei are proposed as a new mechanism to monitor electron states in a nanostructure, or as a means to createn and, if necessary, reshape such nanostructures in the course of the experiment. We found that a polarization of nulear spins may lift the spin polarization of the electron states in a nanostructure and, if sufficiently strong, leads to a polarization of the electron spins. Polarized nuclear spins may form an energy landscape capable of binding electrons with energy up to several meV and the localization radius $>$ 100\AA.Comment: 9 pages, 1 figure, submitted to Physica E, Augist 31, 200

Is the magnetic field necessary for the Aharonov-Bohm effect in mesoscopics?

A new class of topological mesoscopic phenomena in absence of external magnetic field (meso-nucleo-spinics)is predicted, which is based on combined action of the nonequilibrium nuclear spin population and charge carriers spin-orbit interaction . As an example, we show that Aharonov-Bohm like oscillations of the persistent current in GaAs/AlGaAs based mesoscopic rings may exist, in the absence of the external magnetic field, provided that a topologically nontrivial strongly nonequilibrium nuclear spin population is created. This phenomenon is due to the breaking, via the spin-orbit coupling, of the clock wise - anti clock wise symmetry of the charge carriers momentum, which results in the oscillatory in time persistent current.Comment: 14 pages, Late

Quantum Computation in Quantum-Hall Systems

We describe a quantum information processor (quantum computer) based on the hyperfine interactions between the conduction electrons and nuclear spins embedded in a two-dimensional electron system in the quantum-Hall regime. Nuclear spins can be controlled individually by electromagnetic pulses. Their interactions, which are of the spin-exchange type, can be possibly switched on and off pair-wise dynamically, for nearest neighbors, by controlling impurities. We also propose the way to feed in the initial data and explore ideas for reading off the final results.Comment: 12 pages in LaTeX + 1 PostScript figur

Electronic transport through nuclear-spin-polarization-induced quantum wire

Electron transport in a new low-dimensional structure - the nuclear spin polarization induced quantum wire (NSPI QW) is theoretically studied. In the proposed system the local nuclear spin polarization creates the effective hyperfine field which confines the electrons with the spins opposite to the hyperfine field to the regions of maximal nuclear spin polarization. The influence of the nuclear spin relaxation and diffusion on the electron energy spectrum and on the conductance of the quantum wire is calculated and the experimental feasibility is discussed.Comment: 5 pages, 4 figure

Stranger in a Strange Land: Old Chair, New University

There are opportunities and challenges associated with appointing a chair from within and from outside the organization. This discussion will consider multiple aspects and focus on considerations for changing institutions to assume the chair position