Monte Carlo evaluation of trial wavefunctions for the fractional quantized Hall effect: Spherical geometry

Monte Carlo methods have been employed to evaluate trial wave-functions for quantized Hall states and excitations using up to 92 electrons on a sphere. Results are presented for the energy of quasiparticle and quasihole excitations at filling factorv=1/3. These are consistent with extrapolations of exact small system calculations and earlier Monte Carlo results. A trial wavefunction for neutral excitations atv=1/m (m odd integer) is proposed. Results for its excitation energy in the long wavelength limit, atv=1/3, are consistent with those based on the single mode approximation. We have also studied a trial wavefunction representing a quasiparticle excitation involving an electron with reversed spin. Results are presented for the effects on excitation energies of the finite extent of the electron wave function perpendicular to the surface. We have also evaluated the energy of a microscopic trial wave-function for the ground state atv=2/5.Dedicated to Professor Harry Thomas on the occasion of his 60th birthday     

Probing of impurity centers and conduction levels in semiconducting diamond using a MIMS system

A metal-Insulator-Metal-Semiconductor system was used to inject electrons into semiconducting diamond. Light emitted during recombination of these electrons served to monitor the diamond energy levels. The method revealed the distribution of levels in the forbidden gap and conduction levels in diamond.     

Spin-orbit effects in a GaAs quantum dot in a parallel magnetic field

We analyze the effects of spin-orbit coupling on fluctuations of the conductance of a quantum dot fabricated in a GaAs heterostructure. Counterintuitively we argue that spin-orbit effects may become important in the presence of a large parallel magnetic field B( parallel), even if they are negligible for B( parallel) = 0. This should be manifest in the level repulsion of a closed dot, and in reduced conductance fluctuations in dots with a small number of open channels in each lead, for large B( parallel). Our picture is consistent with the experimental observations of Folk et al.     

Identification of superfluid phases of 3He in uniformly isotropic 98.2% aerogel

Superfluid ^{3}He confined to high porosity silica aerogel is the paradigm system for understanding impurity effects in unconventional superconductors. However, a crucial first step has been elusive: exact identification of the microscopic states of the superfluid in the presence of quenched disorder. Using a new class of highly uniform aerogel materials, we report pulsed nuclear magnetic resonance experiments that demonstrate definitively that the two observed superfluid states in aerogel are impure versions of the isotropic and axial p-wave states. The theoretically predicted destruction of long-range orbital order (Larkin-Imry-Ma effect) in the impure axial state is not observed.     

Bulk-edge coupling in the non-Abelian nu=5/2 quantum hall interferometer

Recent schemes for probing non-Abelian statistics in the quantum Hall effect are based on geometries where current-carrying quasiparticles flow along edges that encircle bulk quasiparticles, which are localized. Here we consider one such scheme, the Fabry-Perot interferometer, and analyze how its interference patterns are affected by a coupling that allows tunneling of neutral Majorana fermions between the bulk and edge. While at weak coupling this tunneling degrades the interference signal, we find that at strong coupling, the bulk quasiparticle becomes essentially absorbed by the edge and the intereference signal is fully restored. Furthermore, we find that the strength of the coupling can be tuned by the source-drain voltage.