  The critical behavior of pinned charge density waves (CDW's) is studied as
the threshold for sliding is approached. Using the Fukuyama-Lee-Rice
Hamiltonian with relaxational dynamics, the polarization and linear response
are calculated numerically. ... On the irreversible approach to threshold, the
response due to avalanches triggered by local instabilities dominates the
polarizability, which diverges in one and two dimensions. Characteristic
diverging length scales are studied using finite-size scaling of the
sample-to-sample variations of the threshold field in finite systems and
finite-size effects in the linear polarizability and the irreversible
polarization. A dominant diverging correlation length is found which controls
the threshold field distribution, finite-size effects in the irreversible
polarization, and a cutoff size for the avalanche size distribution. Our
results are compared with those for related models and questions are raised
concerning the relationship of the static critical behavior below threshold to
the dynamic critical behavior in the sliding state above threshold.
