Enhancement of structural rearrangement in glassy sys - tems under shear flow

– We extend the analysis of the mean field schematic model recently introduced [1] for the description of glass forming liquids to the case of a supercooled fluid subjected to a shear flow of rate γ. After quenching the system to a low temperature T , a slow glassy regime is observed before stationarity is achieved at the characteristic time τg. τg is of the order of the usual equilibration time without shear τ o g for weak shear, γτ o g < 1. For larger shear, γτ o g > 1, local rearrangement of dense regions is instead enhanced by the flow, and τg ≃ 1/(T γ). The fluctuation dissipation theorem violation factor X(t1, t1 + ∆t) is explicitly computed: During the glassy evolution X = 1 in the regime ∆t >> t1 whereas, for ∆t << t1, X → 0 in the limit t1 → ∞. Structural rearrangement in supercooled liquids and glassy systems is severely suppressed due to configurational restrictions, requiring a cooperative dynamics of correlated regions that involves many degrees of freedom [2]. This complex behaviour often results in a slow kinetics characterized by diverging relaxation times at the temperature of structural arrest T o [3] and strong non-equilibrium effects, such as aging. A glassy system above T o is generally observed to be off-equilibrium either because a modification of the control parameters, such as the pressure or the temperature, has been exerted or because it is driven mechanically. In many cases it is possible to show that the aging of a system can be triggered by the external forcing and that the system looks younger if a larger drift is applied [4]. This is also witnessed by the modalities of the violation of the fluctuation dissipation theorem (FDT) [5]. In this letter we study the out of equilibrium evolution of a glassy system, such as a supercooled fluid, quenched above T o in the presence of a shear flow with rate γ [6]. The analysis of the dynamics is carried out in the framework of a model [1] recently introduced for the description of the glassy behavior close to the dynamical transition. The approach is