An elasticity theory for structural glasses

Abstract For time intervals smaller than structural relaxation times, we propose an elasticity theory for glasses. Some atoms of the medium, called defect atoms, undergo a soft return force, smaller than that for ordinary atoms; their positions cannot be described by the mere standard displacement field. An extra displacement, relative to the local average current position of surrounding atoms, is needed. Within local stability assumptions, this description yields a microscopic approach to the soft potential model, where coupling and elastic constants have now a common origin. Although their displacements are easy, defect atoms are strongly coupled to the strain of the medium. Then, using a formalism we recently published, the double well structure of the two level systems theory is deduced from this strong coupling.