Condensed Matter Theory

Abstract:

In bilayer quantum Hall systems at filling fractions near nu=1/2+1/2, as the spacing d between the layers is continuously decreased, intralayer correlations must be replaced by interlayer correlations, and the composite fermion (CF) Fermi seas at large d must eventually be replaced by a composite boson (CB) condensate or "111 state" at small d. We propose a scenario where CBs and CFs coexist in two interpenetrating fluids in the transition. Trial wave functions describing these mixed CB-CF states compare very favorably with exact diagonalization results. A Chern-Simons transport theory is constructed that is compatible with experiment.

Abstract:

We develop a phenomenological description of the [Formula presented] quantum Hall state in which the Halperin-Lee-Read theory of the half-filled Landau level is combined with a [Formula presented]-wave pairing interaction between composite fermions (CFs). The electromagnetic response functions for the resulting mean-field superconducting state of the CFs are calculated and used in an RPA calculation of the [Formula presented] and [Formula presented] dependent longitudinal conductivity of the physical electrons, a quantity which can be measured experimentally. © 2003 The American Physical Society.

Abstract:

A brief review is given of the minority game, an idealized model of a market of speculative agents, and its complex many-body behaviour. Particular consideration is given to the consequences and implications of correlations between strategies and different frequencies and timings of adaptation. (C) 2003 Elsevier Science B.V. All rights reserved.