Condensed Matter Seminar
Beyond Kramers: Many-Body Activation and Delay-Induced Escape
Dr. Ohad Shpielberg
Haifa University
Abstract
Thermally activated escape underlies a wide range of phenomena, from chemical reactions and nucleation to transport through complex free-energy landscapes. In equilibrium systems, such processes are traditionally captured by the Kramers problem, leading to exponentially long escape times -- the Arrhenius law. In this talk, I will discuss two complementary routes beyond the Kramers problem and address a central question: how robust is the Arrhenius law?
First, I will present recent results showing that introducing a time delay into the conservative force qualitatively alters the mechanism of thermal activation. Beyond a critical delay, metastable states become dynamically unstable, allowing typical thermal fluctuations to be exponentially amplified. This leads to exponentially accelerated escape rates that can exceed the free-diffusion limit and even reverse the preferred activation pathway without modifying the underlying energy landscape. More broadly, the slingshot mechanism suggests a new route for accelerating the exploration of complex free-energy landscapes. Second, motivated by the broader question of how interactions reshape activated processes, I will discuss recent work on thermal activation in interacting diffusive many-body systems. These studies establish a many-body generalization of the Arrhenius law and reveal two universality classes governing collective activation, showing an incompleteness in Langer's theory of metastability. Together, these results reveal that thermal activation is far less universal than traditionally believed: interactions reshape its collective character, while memory can eliminate its activated nature altogether.
First, I will present recent results showing that introducing a time delay into the conservative force qualitatively alters the mechanism of thermal activation. Beyond a critical delay, metastable states become dynamically unstable, allowing typical thermal fluctuations to be exponentially amplified. This leads to exponentially accelerated escape rates that can exceed the free-diffusion limit and even reverse the preferred activation pathway without modifying the underlying energy landscape. More broadly, the slingshot mechanism suggests a new route for accelerating the exploration of complex free-energy landscapes. Second, motivated by the broader question of how interactions reshape activated processes, I will discuss recent work on thermal activation in interacting diffusive many-body systems. These studies establish a many-body generalization of the Arrhenius law and reveal two universality classes governing collective activation, showing an incompleteness in Langer's theory of metastability. Together, these results reveal that thermal activation is far less universal than traditionally believed: interactions reshape its collective character, while memory can eliminate its activated nature altogether.