Nonlinear effects induced by mechanical stresses in glass-forming systems far from equilibrium

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The elastic-plastic transition in disordered materials often is introduced via thermal activation (glass transition) or strong mechanical deformation close to the rupture point of many oxide or metallic systems. Little is known about the cooperative interaction of atoms/molecules and groups of atoms in the anelastic and nonlinear regime of the response functions due to external stress. If one generally accepts that disordered systems exhibit various modes of structural relaxations (so-called α, ß and fast processes) the frequency dependence of these nonlinear effects is of great interest. It would provide information whether local deformations proceed via α-, β-relaxation modes coupled by the extended stress field surrounding an excitation, or via fast processes and their local change of configuration. We would like to use mechanical spectroscopy to probe the universality of the nonlinear effects in disordered material, particularly in metallic glasses but also in oxide systems and orbital liquids inside crystalline materials. The latter is of prime interest as a rather new class of disordered material and very sensitive to small strain changes.