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The box model, originally introduced to account for the nonresonant hole burning (NHB) dielectric experiments in supercooled liquids, is compared to the measurements of the third harmonics P3 of the polarisation, reported recently in glycerol, close to the glass transition temperature Tg [C. Crauste-Thibierge, C. Brun, F. Ladieu, D. L'Hôte, G. Biroli, and J.-P. Bouchaud, Phys. Rev. Lett. 104, 165703 (2010)]. In this model, each box is a distinct dynamical relaxing entity (hereafter called dynamical heterogeneity (DH)) which follows a Debye dynamics with its own relaxation time τdh. When it is submitted to a strong electric field, the model posits that a temperature increase δTdh, depending on τdh, arises due to the dissipation of the electrical power. Each DH has thus its own temperature increase, on top of the temperature increase of the phonon bath δTph. Contrary to the 'fast' hole burning experiments where δTph is usually neglected, the P3 measurements are, from a thermal point of view, fully in a stationary regime, which means that δTph can no longer be neglected a priori. This is why the version of the box model that we study here takes δTph into account, which implies that the δTdh of the DHs are all coupled together. The value of P3, including both the 'intrinsic' contribution of each DH as well as the 'spurious' one coming from δTph, is computed within this box model and compared to the P3 measurements for glycerol, in the same range of frequencies and temperatures T. Qualitatively, we find that this version of the box model shares with experiments some nontrivial features, e.g., the existence of a peak at finite frequency in the modulus of P3 as well as its order of magnitude. Quantitatively, however, some experimental features are not accounted for by this model. We show that these differences between the model and the experiments do not come from δTph but from the 'intrinsic' contribution of the DHs. Finally, we show that the interferences between the 3ω response of the various DHs are the most important issue leading to the discrepancies between the box model prediction and the experiments. We argue that this could explain why the box model is quite successful to account for some kinds of nonlinear experiments (such as NHB) performed close to Tg, even if it does not completely account for all of them (such as the P3 measurements). This conclusion is supported by an analytical argument which helps understanding how a 'space-free' model as the box model is able to account for some of the experimental nonlinear features. [ABSTRACT FROM AUTHOR]

The impact of the magnetic anisotropy-axis alignment on the collective aging behavior observed in the superspin glass state of the textured and nontextured frozen ferrofluid is analyzed.

Abstract: The existence of a growing correlation length associated with the strong increase of relaxation times of glass-formers close to the glass transition is still a major open question in glass physics. It has been recently proposed that the ac nonlinear susceptibility of a supercooled liquid close to the glass transition temperature T g would be a probe of dynamical correlations. As for spin glasses, where the nonlinear susceptibility diverges at the transition, this quantity is tailored to reveal the possible “hidden” critical behavior of the glass transition. We have developed a high sensitivity experimental device to measure the nonlinear dielectric susceptibility of an insulating material at finite frequency. It measures the third harmonics of the current flowing out of a capacitor with the supercooled liquid as the dielectric layer. It is based on a bridge with two capacitors, and reaches a sensitivity better than 10−7 (ratio of third to first harmonics). Our first results on supercooled glycerol are presented. They clearly reveal the growing of the correlations close to the glass transition. [ABSTRACT FROM AUTHOR]

We report the observation of a surprising phenomenon consisting in a oscillating phase transition which appears in a binary mixture when this is enlightened by a strongly focused infrared laser beam. The mixture is poly-methyl-meth-acrylate (PMMA)-3-octanone, which has an upper critical solution temperature at T(c)=306.6K and volume fraction ϕ(c)=12.8% [Crauste et al., arXiv:1310.6720, 2013]. We describe the dynamical properties of the oscillations, which are produced by a competition between various effects: the local accumulation of PMMA produced by the laser beam, thermophoresis, and nonlinear diffusion. We show that the main properties of this kind of oscillations can be reproduced in the Landau theory for a binary mixture in which a local driving mechanism, simulating the laser beam, is introduced.

We present an innovative technique which allows the simultaneous measurement of the dielectric constant of a material at many frequencies, spanning a four orders of magnitude range chosen between 10(-2) Hz and 10(4) Hz. The sensitivity and accuracy are comparable to those obtained using standard single frequency techniques. The technique is based on three new and simple features: (a) the precise real time correction of the amplification of a current amplifier, (b) the specific shape of the excitation signal and its frequency spectrum, and (c) the precise synchronization between the generation of the excitation signal and the acquisition of the dielectric response signal. This technique is useful in the case of relatively fast dynamical measurements when the knowledge of the time evolution of the dielectric constant is needed.