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 ballistic GaAs quantum dots are reported. Distributions of spacings for both broken (B not equal 0) and unbroken (B = 0) time-reversal symmetry are roughly Gaussian with broad non-Gaussian tails and a standard deviation of 2-6% of the average spacing, comparable to the single-particle level spacing. Spacing distributions for B = 0 are wider by a factor of similar to 1.2 +/- 0.1 compared to B +/- 0, consistent with random matrix theory. Surprisingly, spacing distributions are unimodal, suggesting an absence of spin-degeneracy. Peak width distributions reflect 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.