STATISTICS OF PEAK SPACINGS AND WIDTHS IN THE QUANTUM COULOMB-BLOCKADE REGIME

Measurements of Coulomb blockade conductance peak spacings and widths measured over large ensembles (similar to 10(4) peaks) of peaks in bal listic GaAs quantum dots are reported. Distributions of spacings for b oth broken (B not equal 0) and unbroken (B = 0) time-reversal symmetry are roughly Gaussian with broad non-Gaussian tails and a standard dev iation of 2-6% of the average spacing, comparable to the single-partic le level spacing. Spacing distributions for B = 0 are wider by a facto r of similar to 1.2 +/- 0.1 compared to B +/- 0, consistent with rando m matrix theory. Surprisingly, spacing distributions are unimodal, sug gesting an absence of spin-degeneracy. Peak width distributions reflec t fluctuations in the ''lever arm,'' or capacitance ratio eta = C-gate /C-dot. Field-averaged peak width and spacing both change smoothly as electrons are added to the dot, but fluctuations in peak width appear uncorrelated with spacing fluctuations. (C) 1998 Elsevier Science B.V. All rights reserved.