Probing anomalous relaxation by coherent multidimensional optical spectroscopy

TL;DR

This paper investigates the origin of algebraic decay in correlation functions in complex systems using nonlinear ultrafast laser spectroscopy, predicting specific spectral signatures and aging effects in 2D correlation signals.

Contribution

It introduces a novel approach linking algebraic decay to spectral jumps modeled by a continuous time random walk, with specific predictions for 2D spectroscopy signatures.

Findings

Spectroscopic signatures for stationary ensembles with 1<α<2.

Aging effects in nonstationary ensembles with 0<α<1.

Predicted power-law spectral singularities in 2DCS signals.

Abstract

We propose to study the origin of algebraic decay of two-point correlation functions observed in glasses, proteins, and quantum dots by their nonlinear response to sequences of ultrafast laser pulses. Power-law spectral singularities and temporal relaxation in two-dimensional correlation spectroscopy (2DCS) signals are predicted for a continuous time random walk model of stochastic spectral jumps in a two level system with a power-law distribution of waiting times $\psi (t)\sim t^{-\alpha -1}$. Spectroscopic signatures of stationary ensembles for $1<\alpha <2$ and aging effects in nonstationary ensembles with $0<\alpha <1$ are identified.