Photoinduced Change in the Charge Order Pattern in the Quarter-Filled Organic Conductor(EDO−TTF)2PF6with a Strong Electron-Phonon Interaction

Abstract

The quasistable state in the photoinduced phase transition for the quasi-one-dimensional quarter-filled organic conductor (EDO-TTF)2PF6 has been examined by ultrafast reflective measurements and time-dependent model calculations incorporating both electron-electron and electron-phonon interactions. The transient optical conductivity spectrum over a wide probe photon-energy range revealed that photoexcitation induced a new type of charge-disproportionate state. Additionally, coherent and incoherent oscillations dependent on probe photon energies were found, as predicted by the calculation.

The Earliest Stage of Photoinduced Phase Transition in a Strongly Correlated Organic System Using a 10-fs Pulse

“…This delayed emergence of the photoinduced phase indicates that the PIPT requires a lead time to create the photoinduced phase after photoexcitation. This lead time is already predicted as the delay of charge exchange by the theoretical model calculation in our previous study [6], and the strong electronlattice interaction in this sample causes this lead time.…”

“…The photoinduced state at around 100 fs was assigned to the (1010) photoinduced original phase by measuring the transient reflectivity spectrum ranging from 18 m to 590 nm using a 120-fs pulse [6]. Afterward, the photoinduced phase was found to turn to the charge melting (0.5, 0.5, 0.5, 0.5) metallic phase with time constant of 94 ps by time-resolved infrared vibrational spectroscopy [7].…”

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

“…It exhibits first-order insulator-to-metal (I-M) phase transition at thermal equilibrium and a gigantic ultrafast change of reflectivity under irradiation by a laser pulse in the I phase [5]. * It was shown by time-resolved optical [6,7] and vibrational spectroscopy [8] as well as ultrafast electron diffraction [9] that the photoinduced transformation proceeds stepwise. The initial electronic excited state is trapped at the molecular level within 40 fs following the electron-phonon coupled precursor state [7], while the crystal transformation is driven by slower propagation at the 100 ps time scale.…”

“…The initial electronic excited state is trapped at the molecular level within 40 fs following the electron-phonon coupled precursor state [7], while the crystal transformation is driven by slower propagation at the 100 ps time scale. Actually, different isostructural compounds of the same (EDO-TTF) 2 XF 6 family, where X stands for P, As, or Sb, have already been synthesized. They undergo similar I-M phase transition at thermal equilibrium.…”

Photoinduced Enhancement of the Charge Density Wave Amplitude

“…For instance, charge-lattice coupling creates chargedensity-wave (CDW) order [3,4], while more intricate spin-charge-orbital-lattice coupling leads to combined charge and orbital order in manganites [5,6], or charge-spin stripe order in cuprates [2]. Recent studies suggest that spin order can be generated in iron pnictides in response to excitation of a coherent phonon [7], charge localization can be photoinduced in charge order systems [8], the superconducting order parameter in cuprates can be enhanced via suppression of the competing charge order or the transient redistribution of superconducting coherence [9][10][11], and hidden electronic states can be dynamically accessed [12][13][14][15]. Here we demonstrate a dramatic transient enhancement of the CDW amplitude in elemental chromium (Cr) following photo-excitation.…”