Collective Excitations and Thermodynamics of Disordered State: New Insights into an Old Problem

Disorder has been long considered as a formidable foe of theoretical physicists in their attempts to understand systems behavior. Here we review recently accumulated data and propose that from the point of view of calculating thermodynamic properties the problem of disorder may not be as severe as has been hitherto assumed. We particularly emphasize that contrary to the long held view collective excitations do not decay in disordered systems. We subsequently discuss recent experimental theoretical and modeling results related to collective excitations in disordered media and show how these results pave the way to underestanding thermodynamics of disordered systems glasses liquids supercritical fluids and spin glasses An interesting insight from the recent work is the realization that most important changes of thermodynamic properties of the disordered system are govened only by its fundamental length the interatomic seperation. We discuss how the proposed theory relateds to the previous approaches based on a general many body statistical mechanics framework.