Static and dynamic length scales in glass-forming systems

Walter Kob (Universite Montpellier II, France)

One of the hardest problems in condensed matter physics is to understand why the relaxation dynamics of glass-forming liquids slows down so rapidly if temperature is decreased. In the last 10 years strong evidence has been obtained that this dynamics is increasingly cooperative if temperature is lowered towards the glass transition temperature. Despite intensive investigations, at present very little is known about the mechanism that gives rise to this increasing dynamical length scale. Very recently some evidence has been obtained that glass-forming systems show also an increasing static length scale, which in turn might help to rationalize the dynamics.

In this talk I will discuss a novel approach, the point-to-set correlation functions, that allows to determine relevant static and dynamic length scales in glass-forming liquids. Using this method for the case of a simple glass-former, our computer simulations show that static length scales increase monotonically when the temperature is lowered, whereas the measured dynamic length scale shows a maximum around the critical temperature of mode-coupling theory. Our results demonstrate the existence of a change in the transport mechanism when the glass-former is cooled from moderately to deeply supercooled states across the mode-coupling crossover.

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