Diffusion controlled initial recombination

TL;DR

This paper investigates how initial recombination affects nucleation rates in diffusion-controlled systems, emphasizing its dominance at low temperatures and its impact on kink nucleation in the sine-Gordon model.

Contribution

It introduces a threshold-based approach to analyze initial recombination effects across different dimensions and applies the findings to the sine-Gordon system, highlighting its significance.

Findings

Initial recombination dominates at low temperatures.

Nucleation rate dependence on thresholds decreases with higher dimensions.

Diffusive initial recombination governs kink nucleation rates in the sine-Gordon model.

Abstract

This work addresses nucleation rates in systems with strong initial recombination. Initial (or `geminate') recombination is a process where a dissociated structure (anion, vortex, kink etc.) recombines with its twin brother (cation, anti-vortex, anti-kink) generated in the same nucleation event. Initial recombination is important if there is an asymptotically vanishing interaction force instead of a generic saddle-type activation barrier. At low temperatures, initial recombination strongly dominates homogeneous recombination. In a first part, we discuss the effect in one-, two-, and three-dimensional diffusion controlled systems with spherical symmetry. Since there is no well-defined saddle, we introduce a threshold which is to some extent arbitrary but which is restricted by physically reasonable conditions. We show that the dependence of the nucleation rate on the specific choice of this threshold is strongest for one-dimensional systems and decreases in higher dimensions. We discuss also the influence of a weak driving force and show that the transport current is directly determined by the imbalance of the activation rate in the direction of the field and the rate against this direction. In a second part, we apply the results to the overdamped sine-Gordon system at equilibrium. It turns out that diffusive initial recombination is the essential mechanism which governs the equilibrium kink nucleation rate. We emphasize analogies between the single particle problem with initial recombination and the multi-dimensional kink-antikink nucleation problem.