The challenge in understanding spin glasses - one of the complex states of matter in which Parisi's law has been able to find an order - that has engaged physicists over the past 25 years concerns the property of this particular state of matter at certain temperatures, to evolve very slowly and to age.

The study published in the journal Nature Physics and signed by an Italian-Spanish collaboration, including the Department of Physics research group comprising Giorgio Parisi (Nobel Prize, 2021), Enzo Marinari, Ilaria Paga (CNR-Nanotec) and Federico Ricci Tersenghi, and including on the Spanish side the Universidad Complutense de Madrid, the University of Extremadura and the University of Zaragoza, has shown that if the temperature is lowered further, the system can rejuvenate without forgetting its true age. Practically speaking, when the system grows old, it is learning, and when it rejuvenates, it forgets. However, when the previous conditions are re-established, it returns to remembering and growing old.

The researchers could reproduce these phenomena through numerical simulations on the powerful Janus supercomputer. That allowed the measurement of quantities inaccessible to experiments, which provided evidence that spin glasses can develop 'hidden' orderings of different types simultaneously. The competition between these orderings, which develop with different correlation lengths, is what enables rejuvenation and memory.

These results open up new research perspectives, such as understanding the principles on which biological systems are organised or the possibility of better understanding glassy systems and modelling their capabilities.

References:

Memory and rejuvenation effects in spin glasses are governed by more than one length scale - M. Baity-Jesi, E. Calore, A. Cruz, L. A. Fernandez, J. M. Gil-Narvion, I. Gonzalez-Adalid Pemartin, A. Gordillo-Guerrero, D. Iñiguez, A. Maiorano, E. Marinari, V. Martin-Mayor, J. Moreno-Gordo, A. Muñoz Sudupe, D. Navarro, I. Paga, G. Parisi, S. Perez-Gaviro, F. Ricci-Tersenghi, J. J. Ruiz-Lorenzo, S. F. Schifano, B. Seoane, A. Tarancon & D. Yllanes - Nat. Phys. (2023). https://doi.org/10.1038/s41567-023-02014-6

Further Information

Enzo Marinari 
Department of Physics
enzo.marinari@uniroma1.it

Giorgio Parisi
Department of Physics
giorgio.parisi@uniroma1.it