Crossovers in the dynamics of supercooled liquids probed by an amorphous wall.

We study the relaxation dynamics of a binary Lennard-Jones liquid in the presence of an amorphous wall generated from equilibrium particle configurations. In qualitative agreement with the results presented by Kob et al. [Nat. Phys. 8, 164 (2012).] for a liquid of harmonic spheres, we find that our binary mixture shows a saturation of the dynamical length scale close to the mode-coupling temperature T(c). Furthermore we show that, due to the broken symmetry imposed by the wall, signatures of an additional change in dynamics become apparent at a temperature well above T(c). We provide evidence that this modification in the relaxation dynamics occurs at a recently proposed dynamical crossover temperature T(s) > T(c), which is related to the breakdown of the Stokes-Einstein relation. We find that this dynamical crossover at T(s) is also observed for the harmonic spheres as well as a WCA liquid, showing that it may be a general feature of glass-forming systems.