  Disordered solids respond to quasistatic shear with intermittent avalanches
of plastic activity, an example of the crackling noise observed in many
nonequilibrium critical systems. The temporal power spectrum of activity within
disordered solids consists of three distinct domains: a novel power-law rise
with frequency at low frequencies indicating anticorrelation, white-noise at
intermediate frequencies, and a power-law decay at high frequencies. As the
strain rate increases, the white-noise regime shrinks and ultimately disappears
as the finite strain rate restricts the maximum size of an avalanche. A new
strain-rate- and system-size-dependent scaling theory is derived for power
spectra in both the quasistatic and finite-strain-rate regimes. This theory is
validated using data from overdamped two- and three-dimensional molecular
dynamics simulations. We identify important exponents in the yielding
transition including the dynamic exponent $z$ which relates the size of an
avalanche to its duration, the fractal dimension of avalanches, and the
exponent characterizing the divergence in correlations with strain rate.
Results are related to temporal correlations within a single avalanche and
between multiple avalanches.
