A continuum equation displaying Tracy-Widom distribution in the spatial and temporal fluctuations of growing interfaces

Abstract

A wide variety of surface growth phenomena involves random processes that result in correlated stochastic dynamics. Such dynamics is most succinctly described by a nonlinear equation known as the Kardar-Parisi-Zhang (KPZ) equation. It is of particular interest that the random fluctuations observed along a growing interface described by the KPZ equation turn out to be correlated, with statistics that match the so-called Tracy-Widom distribution. The correlated fluctuations pertain only to the space dimension, namely, along the growing interface. The fluctuations of any given point along the interface over time remain uncorrelated, thus exhibiting Gaussian fluctuations. This is to be expected since the KPZ equation and the experimental systems where the Tracy-Widom statistics have been observed lack mechanisms to induce temporal correlations. Recently, a new mechanism of dissipative self-assembly has been reported, where the self-assembly process is driven by an intrinsic feedback mechanism that is expected to induce temporal correlations. Indeed, such correlations have been experimentally observed with statistics that match the Tracy-Widom probability distribution. Here, we explore the theory of the emergence of correlated temporal fluctuations in such a system when a simplified feedback mechanism is introduced. We develop a highly simplified model, which formally constitutes a modified KPZ equation. We, then, show that this modified equation exhibits temporal fluctuations that are well described by Tracy-Widom fluctuations, up to at least the eight moment, in excellent agreement with the experimental results.