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Heating a crystalline solid increases the average energy of its atoms, molecules, or ions, and the solid gets hotter. At some point, the added energy becomes large enough to partially overcome the forces holding the molecules or ions of the solid in their fixed positions, and the solid begins the process of transitioning to the liquid state or melting. At this point, the temperature of the solid stops rising, despite the continual input of heat, and it remains constant until all of the solid is...
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Generalized fluctuation-dissipation relation and effective temperature upon heating a deeply supercooled liquid.

Nicoletta Gnan1, Claudio Maggi, Giorgio Parisi

  • 1Dipartimento di Fisica, Università di Roma Sapienza, Roma, Italy. nicoletta.gnan@roma1.infn.it

Physical Review Letters
|February 5, 2013
PubMed
Summary

A generalized fluctuation-dissipation relation applies to supercooled liquids when temperature increases. This indicates an effective temperature lower than the bath temperature, relevant for glassy systems.

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Area of Science:

  • Condensed Matter Physics
  • Statistical Mechanics
  • Soft Matter Physics

Background:

  • Supercooled liquids exhibit complex dynamics near the glass transition.
  • The fluctuation-dissipation relation (FDR) is a cornerstone of statistical mechanics, relating equilibrium fluctuations to response functions.
  • Understanding non-equilibrium dynamics in glassy systems is crucial for materials science.

Purpose of the Study:

  • To investigate the applicability of a generalized fluctuation-dissipation relation (FDR) in deeply supercooled liquids subjected to a sudden temperature increase.
  • To characterize the behavior of effective temperature and its connection to phase space dynamics during aging.
  • To assess the relevance of numerical findings for experimental studies on glassy systems.

Main Methods:

  • Numerical simulations of deeply supercooled liquids.
  • Instantaneous temperature increase protocols.
  • Analysis of fluctuation-dissipation relation and effective temperature.
  • Exploration of phase space partitioning and aging dynamics.

Main Results:

  • A generalized FDR was observed upon instantaneously increasing the temperature of a supercooled liquid.
  • The FDR exhibited a two-step shape, mirroring cooling protocols but with an opposite violation.
  • An effective temperature, lower than the bath temperature, was identified and shown to have time dependence.
  • The effective temperature was linked to the partitioned phase space visited during aging.

Conclusions:

  • The study demonstrates the validity of a generalized FDR in a non-equilibrium scenario for supercooled liquids.
  • The concept of effective temperature provides insights into the aging and dynamics of glassy systems.
  • Numerical results offer valuable guidance for experimental investigations of FDR in complex materials.