  Strained amorphous solids often fail mechanically by creating a shear-band.
It had been understood that the shear banding instability is usefully described
as crossing a spinodal point (with disorder) in an appropriate thermodynamic
description. It remained contested however whether the spinodal is critical
(with divergent correlation length) or not. Here we offer evidence for critical
spinodal by using particle pinning. For a finite concentration of pinned
particles the correlation length is bounded by the average distance between
pinned particles, but without pinning it is bounded by the system size.
