Revisiting Multi-Wave Resonance in Classical Lattices: Quasi-Resonances, Not Exact Resonance, Govern Energy Redistribution

TL;DR

This paper shows that in classical lattices, energy redistribution is mainly driven by quasi-resonances rather than exact resonances, with size and nonlinearity affecting their roles in thermalization.

Contribution

It reveals that quasi-resonances, not exact resonances, govern energy transfer and thermalization in classical lattices, highlighting size and nonlinearity effects.

Findings

Exact resonance strength decreases with system size.

Quasi-resonance strength increases with system size.

Quasi-resonances drive energy transfer and thermalization.

Abstract

The multi-wave exact resonance condition is a fundamental principle for understanding energy transfer in condensed matter systems, yet the dynamical evolution of waves satisfying this condition remains unexplored. Here, we reveal that the multi-wave resonant kinetic equations possess distinctive symmetry properties that preferentially induce energy equalization between counter-propagating waves of identical frequency. This initial equalization disrupts the exact resonance condition, rendering it dynamically invalid. We further demonstrate that nonlinearity-mediated multi-wave quasi-resonances--not exact resonances--overn energy transfer and drive the system toward thermalization. Crucially, the strength of exact resonances decays with increasing system size, while quasi-resonance strength grows. Moreover, exact resonance strength remains independent of nonlinearity, whereas quasi-resonance strength diminishes with reduced nonlinearity. These observations provide additional evidence supporting the aforementioned conclusion while elucidating the size-dependent thermalization characteristics in lattice systems.