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Kovacs Memory Effect in a Thin Granular Layer: Experimental Evidence and Its Physical Origin

Francisco Vega Reyes1,*, Álvaro Rodríguez-Rivas2,†, Pablo Maynar3,‡, and M. Isabel García de Soria3,§

  • 1Departamento de Física and Instituto de Computación Científica Avanzada (ICCAEx), Universidad de Extremadura, 06071 Badajoz, Spain
  • 2Departamento de Matemática Aplicada II, Universidad de Sevilla, E. T. S. de Ingeniería, C. de los Descubrimientos, s/n. Pabellón Plaza de América 41092 Sevilla (Spain)
  • 3Física Teórica, Universidad de Sevilla, Apartado de Correos 1065, 41080 Sevilla, Spain

  • *Contact author: fvega@eaphysics.xyz
  • †Contact author: arodriguezrivas@us.es
  • ‡Contact author: maynar@us.es
  • §Contact author: gsoria@us.es
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Phys. Rev. Lett. 137, 208201 – Published 10 November, 2026

DOI: https://doi.org/10.1103/791d-2tx9

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.

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Physics Subject Headings (PhySH)

synopsis

Granular Matter Carries Hidden Memory

Published 10 November, 2026

A memory phenomenon known as the anomalous Kovacs effect has been experimentally observed in a granular system for the first time.

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References (40)

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Phys. Rev. Lett. 137, 208201– Published 10 November, 2026
  • Received 25 February 2026
  • Accepted 9 September 2026
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