Unveiling diffusive states from center-of-mass trajectories in glassy dynamics

Area of Science:

• Condensed Matter Physics
• Statistical Mechanics
• Materials Science

Background:

• Glassy dynamics involve complex molecular motion, often characterized by alternating free and trapped diffusive states.
• Understanding these transitions is crucial for characterizing material properties, particularly in supercooled liquids.
• Existing methods may struggle to precisely differentiate and quantify these distinct diffusive regimes.

Purpose of the Study:

• To propose and validate a novel method for detecting alternating diffusive states (free and trapped) in materials.
• To establish control parameters for this method based on measurable quantities like mean square displacement and non-Gaussianity.
• To apply the method to analyze molecular dynamics simulation data of supercooled liquids.

Main Methods:

• Development of a stochastic model simulating alternating diffusive states, incorporating the Ornstein-Uhlenbeck process for trapped states.
• Utilizing mean square displacement and the non-Gaussianity parameter as key control parameters for state detection.
• Validation of the method's efficacy under conditions of distinct diffusivities and sufficiently long state durations.

Main Results:

• The proposed method successfully identifies alternating free and trapped diffusive states.
• Control parameters derived from mean square displacement and non-Gaussianity effectively characterize these states.
• Application to supercooled liquids reveals long-lived trapped states, with their sojourn-time distribution exhibiting power-law behavior near the glass transition temperature.

Conclusions:

• The developed method provides a robust framework for analyzing complex diffusive dynamics in materials.
• It offers insights into the nature of trapped states in glassy systems, particularly their persistence and distribution near the glass transition.
• This approach is valuable for studying supercooled liquids and other systems exhibiting intermittent dynamics.