Local response to light excitation in the charge-ordered phase of(EDO−TTF)2SbF6

Abstract

The family of materials (EDO-TTF) 2 XF 6 represents quasi-one-dimensional quarter filled systems exhibiting insulator-to-metal (I-M) phase transition at thermal equilibrium. (EDO-TTF) 2 PF 6 is known to undergo a photoinduced I-M conversion with cooperative response to light excitation. Here we use femtosecond pump-probe experiments to study the photoresponse of (EDO-TTF) 2 SbF 6 made of a larger counteranion SbF 6 compared to the well studied (EDO-TTF) 2 PF 6 . In the early stage of the photoinduced process, we reveal a multicomponent coherent oscillating feature. The evolution of this feature with excitation density and temperature points to the local nature of the photoswitching in (EDO-TTF) 2 SbF 6 . At longer time scale, we did not detect the features associated with the transformation to the M phase, albeit observed in the PF 6 derivative. We propose a scenario whereby the bigger size of the counteranion in (EDO-TTF) 2 SbF 6 hinders the establishment of this transformation at macroscopic scale.

Activation of coherent lattice phonon following ultrafast molecular spin-state photo-switching: A molecule-to-lattice energy transfer

“…Such low frequency modes in the 30 cm −1 range are usually associated to large amplitude ligand torsion (Ronayne et al , 2006). In molecular solids, this frequency range also corresponds to inter-molecular optical phonons, mixing molecular displacement and torsion (Uemura and Okamoto, 2010 and Servol et al , 2015). It seems therefore difficult to discriminate from these results the nature of such a mode.…”

“…The light-control of molecular transformations expands nowadays towards materials science, offering new opportunities to impact the macroscopic state of materials with a light pulse (Koshihara, 2009). Molecular crystals are promising systems composed of many interacting elements which can give rise to collective transformations as ferroelectricity (Collet et al , 2003; Okamoto et al , 2004; and Uemura and Okamoto, 2010) or metal-insulator transitions for instance (Chollet et al , 2005; Kawakami, 2009; Gao et al , 2013; and Servol et al , 2015). In such systems, the charge redistributions induced by light at the intra- and inter-molecular levels activate (through the couplings between charge and structural degrees of freedom) coherent optical phonons in the early stages of the transformation, which results from the energy redistribution from the absorbing centers to the molecular and lattice degrees of freedom.…”

Optical Study of Electronic Structure and Photoinduced Dynamics in the Organic Alloy System [(EDO-TTF)0.89(MeEDO-TTF)0.11]2PF6

“…The cooperation/competition of several types of interactions, including electron-electron, electron-lattice, and donor-anion interactions, must be regarded as important factors for realization of the unique low-T insulating phase of (EDO-TTF) 2 PF 6 and its photoinduced dynamics. Therefore, a comparative study of photoinduced dynamics in similar classes of materials with different physical parameter values is essential to understanding of the roles of these interactions in each material's photo-response [19][20][21]. Here we present the first report of a study on the dynamics of the photoinduced phase transition process in the organic alloy system [(EDO-TTF) 0.89 (MeEDO-TTF) 0.11 ] 2 PF 6 (MeEDO-TTF = 4,5-ethylenedioxy-4 -methyltetrathiafulvalene), which shows a quite different class of M-I phase transition than that of (EDO-TTF) 2 PF 6 despite the similarity of crystal structure in high-T metallic phase.…”

Photoinduced transition to charge-ordered phases from dynamical localization in the metallic phase of α−(BEDT-TTF)2I3

“…The transitions investigated so far have been towards destroying the order of the ground state, but photoinduced phenomena in the reverse direction have been observed recently. It has been reported that the electronic order of a charge density wave, [6][7][8] a spin density wave, 9 superconductivity, [10][11][12] ferroelectricity, 13 and charge order [14][15][16][17][18] is enhanced by photoexcitation. We investigate one of these counterintuitive phenomena in α-(BEDT-TTF) 2 I 3 (BEDT-TTF: bis[ethylenedithio]tetrathiafulvalene).…”