Coherent Control of Charge and Lattice Dynamics in a Photoinduced Neutral-to-Ionic Transition of a Charge-Transfer Compound

Abstract

Coherent control of a charge-lattice coupled oscillation associated with the neutral (N)-ionic (I) transition was successfully demonstrated for a charge-transfer (CT) compound, tetrathiafulvalene-p-chloranil, with use of double femtosecond laser pulses. By changing the interval of the two laser pulses, amplitude of the oscillation in the reflectivity for the intramolecular transition band sensitive to the degree of CT was periodically changed. With increase of the pump intensity, the oscillation amplitude was dramatically enhanced. Such an enhancement is discussed in terms of the cooperative nature of the N-I transition.

Tracking the evolution of electronic and structural properties of VO2during the ultrafast photoinduced insulator-metal transition

“…where a complete structural phase transition results, is fundamentally different to those found in highly excited materials where no phase transition results, such as charge transfer compounds 40 , organic solids 41,42 or bismuth. In these cases, photoexcitation increases the dephasing rate and softens the phonon modes, but does not result in an underlying change in the symmetry of the lattice potential on an ultrafast timescale [43][44][45] .…”

State of the art and opportunities in probing photoinduced phase transitions in molecular materials by conventional and picosecond X-ray diffraction

“…For instance, coherent oscillations were observed for different molecular materials (Buron and Collet, 2005;Koshihara and Kuwata-Gonokami, 2006;Iwai et al, 2006;Chollet et al, 2005) and are believed to be associated with coherent atomic motions. A more complicated case of nanostructured materials has been also reported (Bargheer et al, 2004).…”

Infrared Investigations of the Neutral-Ionic Phase Transition in TTF-CA and Its Dynamics

“…From that, we can deduce that in both cases the conductivity contributions are thermally activated or optically excited NIDWs, respectively. This pioneer ingreport [69] triggered numerous studies [70,76,[85][86][87] of the PIPT aiming to examine the creation process of the neutral domains in the ionic phase. Most of the studies were performed at two temperatures: either very close to the transition (approximately 78 K) or for a very low temperature (∼4 K).…”

“…Finally, the electronic system couples to the underlying lattice and excites phonons [87] via electron-phonon coupling; i.e., shock-waves are generated. They can convert neighboring chains into neutral domains (Figure 21f).…”

“…As discussed in Section 4.2, the symmetric a g modes become infrared activated in the ionic phase due to the dimerization of the molecules along the a-direction. This effect is a unique property of the ionic phase; thus it will be utilized to measure the presence of the ionic state and how it vanishes with time [87]. In Figure 24a, the time-dependent behavior of the reflectivity change ∆ t R = R(t) − R(0) at T = 78 K and for a laser pulse intensity of 0.71 mJ/cm 2 is directly compared with the variation of the static reflectivity upon passing through neutral-ionic phase transition ∆ T R = R 85K − R 79K .…”