The Gardner’s phase

Low temperature glasses display all kinds of anomalies: anormal heat and thermal conductivity; abundance of localized vibration modes; plastic and irreversible response to arbitrarily small stress amplitudes.
Once the liquid is trapped in a particular glass, one could imagine that the transport properties would result, as in a crystal, from the vibrations of the particles around their mean positions, these defining an underlying network. In the case of glasses, the latter is disordered and it is expected that there will be significant differences between the properties of transport in crystals and glasses. However, from this point of view, a glass would ultimately be not so much more complicated than a disordered crystal. However this vision does not account for the observed anomalies.

Very recent theoretical work has shown that these anomalies can be understood as the remanence of a new phase transition - the Gardner transition, which distinguishes two types of amorphous solids: mechanically stable single glass and marginally stable glass. Numerical simulations in finite dimension have confirmed the existence of this transition and shown that it is associated with a heterogeneous organization of the vibrations of the particles within the cages formed by their neighbors.

On the basis of this image of cages, we obtained the first experimental confirmation of the existence of the Gardner phase in a granular glass in collaboration with Antoine Seguin (Laboratoire FAST). We followed the individual trajectories of the particles composing a vibrated granular medium. In a first step, by adiabatic compression, we formed a granular glass in which each particle vibrates in a cage formed by its neighbors. We then demonstrated that there exists a density beyond which the cages divide into several « intra-cages" defined by the neighboring particles with which the collisions dominates. The local minimum of free energy corresponding to the glass breaks up into a plethora of minima as the density increases. No significant barrier separating them, all these minima are marginally stable, hence the anormal properties of the glasses in the Gardner phase.
Seguin, A., & Dauchot, O. (2016). Experimental Evidence of the Gardner Phase in a Granular Glass. Prl, 117(22), 228001–5.


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Mechanical Response of a Glass

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