Van der Waals-Zeeman Colloquium

Tuesday, 25 Sep 2007, 16:00h

Effective temperatures in driven systems

Prof. Andrea Liu
Condensed Matter Phyisics, Univ. of Pennsylvania

In an equilibrium system, temperature not only influences the average properties of a system, such as its pressure or density, but also controls the fluctuations around those averages. In systems driven far from equilibrium, however, temperature is no longer well-defined, and fluctuations can be non-thermal in origin. I will discuss a class of such systems, namely steadily-sheared glasses, for which there is a considerable body of evidence that the idea of an effective temperature is useful, at least in certain regimes. Using nonequilibrium molecular dynamics simulations, we have now calculated seven different definitions that yield a consistent value for the effective temperature, which can be many orders of magnitude higher than the bath temperature. However, if we want to understand the behavior of a material, measuring its temperature is only a start. I will discuss recent results that show that the effective temperature plays a critical role in determining materials properties such as the extreme slowing down of the dynamics as the system jams.