Abdoli I, Löwen H, Sommer J-U, Sharma A
Leibniz-Institut für Polymerforschung Dresden, Institut Theorie der Polymere, 01069 Dresden, Germany.
Institut für Theoretische Physik II: Weiche Materie, Heinrich-Heine-Universität Düsseldorf, Düsseldorf 40225, Germany.
J Chem Phys. 2023 Mar 14;158(10):101101. doi: 10.1063/5.0139830.
The probability per unit time for a thermally activated Brownian particle to escape over a potential well is, in general, well-described by Kramers's theory. Kramers showed that the escape time decreases exponentially with increasing barrier height. The dynamics slow down when the particle is charged and subjected to a Lorentz force due to an external magnetic field. This is evident via a rescaling of the diffusion coefficient entering as a prefactor in the Kramers's escape rate without any impact on the barrier-height-dependent exponent. Here, we show that the barrier height can be effectively changed when the charged particle is subjected to a vortex flow. While the vortex alone does not affect the mean escape time of the particle, when combined with a magnetic field, it effectively pushes the fluctuating particle either radially outside or inside depending on its sign relative to that of the magnetic field. In particular, the effective potential over which the particle escapes can be changed to a flat, a stable, and an unstable potential by tuning the signs and magnitudes of the vortex and the applied magnetic field. Notably, the last case corresponds to enhanced escape dynamics.
一般来说，热激活布朗粒子越过势垒的单位时间概率可以用克莱默斯理论很好地描述。克莱默斯表明，逃逸时间随着势垒高度的增加呈指数下降。当粒子带电并由于外部磁场而受到洛伦兹力时，动力学过程会减慢。这通过重新标度扩散系数很明显，该扩散系数作为前置因子进入克莱默斯逃逸率，而对依赖于势垒高度的指数没有任何影响。在这里，我们表明，当带电粒子受到涡旋流作用时，势垒高度可以有效地改变。虽然单独的涡旋不会影响粒子的平均逃逸时间，但当与磁场结合时，它会根据其相对于磁场的符号有效地将波动的粒子径向向外或向内推动。特别地，通过调整涡旋和外加磁场的符号和大小，可以将粒子逃逸所经过的有效势改变为平坦势、稳定势和不稳定势。值得注意的是，最后一种情况对应于增强的逃逸动力学。
