The Kovacs memory effect in a thin granular layer: experimental evidence and its physical origin

TL;DR

This study experimentally observes and theoretically explains the Kovacs memory effect in a thin vibrated granular layer, revealing how memory emerges during fast transients and is governed by kinetic and hydrodynamic regimes.

Contribution

It provides the first experimental evidence of the Kovacs effect in granular layers and develops a kinetic theory framework to explain its physical origin.

Findings

Memory appears during fast transients due to temperature coupling.

Memory vanishes quickly, leading to a memoryless regime.

Molecular dynamics simulations confirm experimental and theoretical results.

Abstract

We report the experimental observation of memory effects in a vertically vibrated thin granular layer. Following a quench in the input acceleration, the granular temperature exhibits an anomalous Kovacs memory effect confined to the initial fast relaxation stage. This memory vanishes shortly thereafter, yielding a time-dependent memoryless regime governed solely by the instantaneous temperature before the system reaches its final steady state. We develop a kinetic theory framework that quantitatively captures these features by identifying the initial memory and subsequent memoryless regimes with the kinetic and hydrodynamic states, respectively (that are well established in kinetic theory). Our analysis reveals that memory emerges during fast transients through coupling between horizontal and vertical temperatures, a mechanism that fundamentally constrains the accessible memory phenomenology and precludes observation of the standard Kovacs effect in this system. Molecular dynamics simulations provide independent confirmation of all experimental and theoretical findings.