A Variational Ground-State for the ν=2/3\nu=2/3 Fractional Quantum Hall Regime

A variational $\nu=2/3$ state, which unifies the sharp edge picture of MacDonald with the soft edge picture of Chang and of Beenakker is presented and studied in detail. Using an exact relation between correlation functions of this state and those of the Laughlin $\nu=1/3$ wavefunction, the correlation functions of the $\nu=2/3$ state are determined via a classical Monte Carlo calculation, for systems up to $50$ electrons. It is found that as a function of the slope of the confining potential there is a sharp transition of the ground state from one description to the other. This transition should be observable in tunneling experiments through quantum dots.Comment: 14 pages + 4 uuencoded figure

Thermal Phase Transition in Two-Dimensional Disordered Superconductors: Kosterlitz-Thouless vs Percolation

Weakly disordered two-dimensional superconductors undergo a Kosterlitz-Thouless (KT) transition, where at a critical temperature vortices proliferate through the system and destroy the superconducting (SC) order. On the other hand, it was suggested that for large disorder the systems separates into regions of high SC order, and it is the percolation of coherence between these regions that is lost at the critical temperature. Here we demonstrate that these two descriptions are just the dual of each other. A vortex causes loss of local correlations, and thus the loss of percolation of correlations is concomitant with percolation of vortices on the dual lattice, in the perpendicular direction, i.e. the KT transition.Comment: 4 pages, 5 figure

Suppression of Shot Noise in Quantum Point Contacts in the "0.7" Regime

Experimental investigations of current shot noise in quantum point contacts show a reduction of the noise near the 0.7 anomaly. It is demonstrated that such a reduction naturally arises in a model proposed recently to explain the characteristics of the 0.7 anomaly in quantum point contacts in terms of a quasi-bound state, due to the emergence of two conducting channels. We calculate the shot noise as a function of temperature, applied voltage and magnetic field, and demonstrate an excellent agreement with experiments. It is predicted that with decreasing temperature, voltage and magnetic field, the dip in the shot noise is suppressed due to the Kondo effect.Comment: 4 pages, 1 figur