Emergence of Dynamical Coherence in a Driven One-dimensional Interacting Rotor Model

Abstract: In order to understand the dynamics of active matter, we examine a minimalistic model where interacting spins on a one-dimensional lattice are driven by a self-propelled spin at the centre with a fixed rotational velocity $({\omega}{0})$. The other spins execute rotational Brownian motion by following the Shore-Zwanzig model of rotational dynamics. The simplicity of the model allows us to inquire about several relevant microscopic quantities. The continuous 'active' torque on the central spin is propagated through nearest neighbour interactions with a uniform coupling parameter, J. We have found a bounded region in the J-${\omega}{0}$ plane where the system exhibits 'active matter like behaviour'. Interestingly, in the limits of large J and ${\omega}_{0}$, we observe a 'slipping behaviour'. The site specific average rotational velocity of the spin, as one moves away from the central spin exhibits a nearly exponential decay with distance, allowing the definition of a correlation length $({\xi})$ which grows rapidly with an increase of the coupling (J) between the spins. Site specific average velocity exhibits a change from a single exponential to biexponential decay pattern as the system enters the active region of the phase diagram, accompanied by a non-monotonic behavior of the correlation length. We conclude that a macroscopic coherent state can emerge in the presence of a small concentration of active molecules. We discuss experimental relevance of our results.