Understanding the Nonlinear Dynamics of Driven Particles in Supercooled Liquids in Terms of an Effective Temperature

TL;DR

This paper develops a theoretical framework linking the nonlinear response of driven particles in supercooled liquids to an effective temperature derived from the Potential Energy Landscape, explaining material thinning near the glass transition.

Contribution

It introduces a quantitative model connecting mechanical thinning under force to an effective temperature based on PEL properties, advancing understanding of out-of-equilibrium glassy dynamics.

Findings

Mechanical properties mimic those of a system at higher temperature.

Effective temperature is observable-independent and affects thermodynamic and dynamic properties.

Theoretical estimates of effective temperature dependence on temperature and force are provided.

Abstract

In active microrheology the mechanical properties of a material are tested by adding probe particles which are pulled by an external force. In case of supercooled liquids, strong forcing leads to a thinning of the host material which becomes more pronounced as the system approaches the glass transition. In this work we provide a quantitative theoretical description of this thinning behavior based on the properties of the Potential Energy Landscape (PEL) of a model glass-former. A key role plays the trap-like nature of the PEL. We find that the mechanical properties in the strongly driven system behave the same as in a quiescent system at an enhanced temperature, giving rise to a well-characterized effective temperature. Furthermore, this effective temperature turns out to be independent of the chosen observable and individually shows up in the thermodynamic and dynamic properties of the system. Based on this underlying theoretical understanding, we can estimate its dependence on temperature and force by the PEL-properties of the quiescent system. We furthermore critically discuss the relevance of effective temperatures obtained by scaling relations for the description of out-of-equilibrium situations.