Slow stretched-exponential and fast compressed-exponential relaxation from local event dynamics

Area of Science:

• Condensed matter physics
• Materials science
• Statistical mechanics

Background:

• Liquids and glasses exhibit complex particle dynamics.
• Understanding relaxation processes is crucial for material properties.
• Existing models may not fully capture the crossover between different relaxation behaviors.

Purpose of the Study:

• To propose a novel atomistic model for correlated particle dynamics in liquids and glasses.
• To explain the co-existence of slow stretched-exponential relaxation (SER) and fast compressed-exponential relaxation (CER).
• To reproduce experimentally observed phenomena, including temperature dependence and the SER-CER crossover in metallic glasses.

Main Methods:

• Development of an atomistic model based on elastically interacting local relaxation events.
• Analysis of the model's predictions for particle dynamics across different temperature regimes.
• Comparison of model predictions with experimental data for relaxation behavior.

Main Results:

• The model successfully predicts both SER and CER.
• SER is attributed to the slowing down of local relaxation events due to elastic interactions.
• CER is linked to avalanche-like dynamics in the low-temperature glass state.
• The model reproduces the temperature dependence of SER and CER, including Debye decay at high temperatures.
• The model accurately reproduces the SER to CER crossover observed in metallic glasses.

Conclusions:

• The proposed atomistic model provides a unified framework for understanding correlated particle dynamics in liquids and glasses.
• The model elucidates the microscopic origins of SER and CER and their crossover behavior.
• This work offers insights into the fundamental physics governing the glass transition and relaxation dynamics in disordered materials.