On the transient Fluctuation Dissipation Theorem after a quench at a critical point

TL;DR

This study experimentally verifies the Modified Fluctuation Dissipation Theorem during the transient relaxation of a liquid crystal near a critical point, demonstrating its applicability beyond equilibrium conditions.

Contribution

It provides experimental validation of MFDT in a non-equilibrium transient state close to a critical point, extending its relevance to systems described by Landau-Ginzburg theory.

Findings

MFDT is verified during the transient relaxation.

Standard FDT does not hold out of equilibrium.

Results are relevant for material aging studies.

Abstract

The Modified Fluctuation Dissipation Theorem (MFDT) proposed by G. Verley et al. {\it (EPL 93, 10002, (2011))} for non equilibrium transient states is experimentally studied. We apply MFDT to the transient relaxation dynamics of the director of a liquid crystal after a quench close to the critical point of the Fr\'eedericksz transition (Ftr), which has several properties of a second order phase transition driven by an electric field. Although the standard Fluctuation Dissipation Theorem (FDT) is not satisfied, because the system is strongly out of equilibrium, the MFDT is perfectly verified during the transient in a system which is only partially described by Landau-Ginzburg (LG) equation, to which our observation are compared. The results can be useful in the study of material aging.