Optical freezing of charge motion in an organic conductor

TL;DR

This study demonstrates optical freezing of charge motion in an organic conductor using an intense ultrafast infrared pulse, inducing charge localization by dynamically reducing electronic transfer integral t.

Contribution

It presents the first experimental observation of charge localization induced by ultrafast optical fields in an organic conductor, revealing a new method to control electronic states.

Findings

Reflectivity change of over 25% indicating charge localization.

Observation of coherent charge oscillations along the time axis.

Reduction of transfer integral t by approximately 10% due to the electric field.

Abstract

Dynamical localization, i.e., reduction of the intersite electronic transfer integral t by an alternating electric field, E(omega) , is a promising strategy for controlling strongly correlated systems with a competing energy balance between t and the Coulomb repulsion energy. Here we describe a charge localization induced by the 9.3 MV/cm instantaneous electric field of a 1.5 cycle (7 fs) infrared pulse in an organic conductor alpha-(bis[ethylenedithio]-tetrathiafulvelene)_2I_3. A large reflectivity change of > 25% and a coherent charge oscillation along the time axis reflect the opening of the charge ordering gap in the metallic phase. This optical freezing of charges, which is the reverse of the photoinduced melting of electronic orders, is attributed to the 10% reduction of t driven by the strong, high-frequency (omega>t/h_bar) electric field.