Nonlinear plastic modes in disordered solids

We propose a theoretical framework within which a robust micromechanical definition of precursors to plastic instabilities, often termed soft spots, naturally emerges. They are shown to be collective displacements (modes) ˆz that correspond to local minima of a barrier function b(ˆz), which depends solely on inherent structure information. We demonstrate how some heuristic searches for local minima of b(ˆz) can a priori detect the locus and geometry of imminent plastic instabilities with remarkable accuracy, at strains as large as γ_c−γ∼10⁻² away from the instability strain γ_c. Our findings suggest that the a priori detection of the entire field of soft spots can be effectively carried out by a systematic investigation of the landscape of b(ˆz).