Point-to-set dynamic length scale in binary Lennard-Jones glass-formers

Area of Science:

• Condensed Matter Physics
• Computational Materials Science
• Statistical Mechanics

Background:

• The temperature dependence of the point-to-set dynamic length scale (ξ_c^dyn) in glass-forming systems is crucial for understanding liquid behavior.
• Previous studies suggested non-monotonic T-dependence of ξ_c^dyn in harmonic (HM) systems arises from wall effects, not bulk liquid properties.
• A discrepancy was noted with prior work on Lennard-Jones (LJ) systems reporting monotonic behavior.

Purpose of the Study:

• To investigate the temperature-dependent behavior of ξ_c^dyn in Lennard-Jones (LJ) systems.
• To clarify the role of wall effects versus intrinsic liquid properties on the observed ξ_c^dyn behavior.
• To reconcile conflicting findings regarding the T-dependence of ξ_c^dyn in different simulation models.

Main Methods:

• Employing molecular dynamics (MD) simulations.
• Utilizing the specific Lennard-Jones (LJ) system parameters from Hocky et al.
• Systematically varying geometry size (d) to analyze finite-size and wall effects.

Main Results:

• A non-monotonic temperature dependence of ξ_c^dyn was observed in the simulated LJ system.
• The formation of a peak in ξ_c^dyn with respect to temperature was demonstrated to be a consequence of wall effects.
• A new non-monotonic behavior was identified, linking the maximum of a characteristic time ratio to the maximum of ξ_c^dyn, confirming its origin in sandwiched geometries.

Conclusions:

• The non-monotonic temperature dependence of ξ_c^dyn is a natural property of liquids confined in a sandwiched geometry, driven by wall effects.
• Unlike HM systems, the characteristic temperature T_max-c in LJ systems can be above, at, or below the mode-coupling temperature T_c.
• The study implies that the link between dramatic changes near T_c and non-monotonic ξ_c^dyn evolution, as suggested by random first-order transition theory, is not universally necessary.