Physical Society Colloquium

Interview for Faculty Position

Theoretical Studies on Fluctuations in Single Molecule Spectra and Supercooled Liquids:
Probing Dynamical Heterogeneities in Space and Time

YounJoon Jung

UC Berkeley

In the first part of the talk, I will present theoretical studies of time-dependent fluctuations in single molecule spectroscopy in a dynamic environment. In particular, I focus on the photon counting statistics of a single molecule in a fluctuating environment. I show that fluctuations of photon counts are described by a three-time correlation function in the linear response limit, thus generalizing the Wiener-Khintchine formalism. I consider two examples to illustrate how fluctuations in photon counts can yield unique dynamical information on a single molecule and its local environments: a simple spectral diffusion process with a finite timescale and a blinking behavior of quantum dots exhibiting power-law behavior without any finite timescales.

In the second part of the talk, I will describe recent theoretical development of dynamical arrests in supercooled liquids and glasses. Based on the idea of dynamical facilitations and local excitations, dynamical heterogeneity is described as excitation lines in space-time trajectory. Motivated by recent experiments of self-diffusions and single molecule rotations, I perform numerical simulations of the diffusion process, and find decoupling phenomena between structural relaxation and diffusions in the fluctuation-dominated regime. I will also describe statistics of exchange times of supercooled liquids, and their implications in recent single molecule measurements.