Response Function Theory for Many-Body Systems away-from Equilibrium: Conditions of Ultrafast-Time and Ultrasmall-Space Experimental Resolution

TL;DR

This paper develops a Response Function and Scattering Theory for analyzing ultrafast and nanoscale nonequilibrium systems, linking observable properties with correlation functions and susceptibilities, with applications in ultrafast spectroscopy and Raman scattering.

Contribution

It introduces a generalized response function framework for nonequilibrium many-body systems with space and time resolution, including a fluctuation-dissipation theorem and Green functions.

Findings

Derived a generalized fluctuation-dissipation theorem for nonequilibrium systems.

Applied the formalism to ultrafast laser spectroscopy and Raman scattering.

Established connections between observables and correlation functions out of equilibrium.

Abstract

A Response Function Theory and Scattering Theory applicable to the study of physical properties of systems driven arbitrarily away from equilibrium, specialized for dealing with ultrafast processes and in conditions of space resolution (including nanometric scale), are presented. The derivation is done in the framework of a Gibbs-style Nonequilibrium Statistical Ensemble Formalism. It is shown the connection of the observable properties with time and space-dependent correlation functions out of equilibrium. A generalized fluctuation-dissipation theorem, which relates these correlation functions with generalized susceptibilities is derived. It is also presented the method, useful for calculations, of nonequilibrium-thermodynamic Green functions. A couple of illustration with application of the formalism, consisting of the study of optical responses in ultrafast laser spectroscopy and Raman Scattering of electrons in III-N semiconductors (of "blue diodes") driven away from equilibrium by action of electric fields of moderate to high intensities, are described.