Collective stochastic resonance in shear-induced melting of sliding bilayers

The far-from-equilibrium dynamics of two crystalline two-dimensional monolayers driven past each other is studied using Brownian dynamics simulations. While at very high and low driving rates the layers slide past one another retaining their crystalline order, for intermediate range of drives the system alternates irregularly between the crystalline and fluid-like phases. A dynamical phase diagram in the space of interlayer coupling and drive is obtained. A qualitative understanding of this stochastic alternation between the liquid-like and crystalline phases is proposed in terms of a reduced model within which it can be understood as a stochastic resonance for the dynamics of collective order parameter variables. This remarkable example of stochastic resonance in a spatially extended system should be seen in experiments which we propose in the paper.Comment: 12 pages, 18 eps figures, minor changes in text and labelling of figures, accepted for publication in Phys. Rev.

Flow-induced currents in nanotubes: a Brownian dynamics approach

Motivated by recent experiments [Science {\bf 299}, 1042 (2003)] reporting that carbon nanotubes immersed in a flowing fluid displayed an electric current and voltage, we numerically study the behaviour of a collection of Brownian particles in a channel, in the presence of a flow field applied on similar but slower particles in a wide chamber in contact with the channel. For a suitable range of shear rates, we find that the flow field induces a unidirectional drift in the confined particles, and is stronger for narrower channels. The average drift velocity initially rises with increasing shear rate, then shows saturation for a while, thereafter starts decreasing, in qualitative agreement with recent theoretical studies [Phys. Rev. B {\bf 70}, 205423 (2004)] based on Brownian drag and ``loss of grip''. Interestingly, if the sign of the interspecies interaction is reversed, the direction of the induced drift remains the same, but the flow-rate at which loss of grip occurs is lower, and the level of fluctuations is higher.Comment: 7 pages, 9 figure