Ultrafast modulation of polarization amplitude by terahertz fields in electronic-type organic ferroelectrics

Abstract

Ferroelectrics sometimes show large electro-optical and non-linear optical effects, available for polarization rotation and frequency conversion of light, respectively. If the amplitude of ferroelectric polarization is modulated in the picosecond time domain, terahertz repetition of optical switching via electro-optical and non-linear optical effects would be achieved. Here we show that polarization amplitude can be rapidly modulated by a terahertz electric field in an organic ferroelectric, tetrathiafulvalene-p-chloranil (TTF-CA). In this compound, alternately stacked donor (TTF) and acceptor (CA) molecules are dimerized via the spin-Peierls mechanism, and charge transfer within each dimer results in a new type of ferroelectricity called electronic-type ferroelectricity. Using a terahertz field, the intradimer charge transfer is strongly modulated, producing a subpicosecond change in the macroscopic polarization, which is demonstrated by transient reflectivity and second-harmonic generation measurements. Subsequently, coherent oscillation of the dimeric molecular displacements occur, which is explained by the modulation of the spin moment of each molecule.

Terahertz-field-induced polar charge order in electronic-type dielectrics

“…If the inversion symmetry is lost, the secondorder nonlinear optical response such as SHG should be observed. Note that in organic molecular materials such as TTF-CA and α-(ET) 2 I 3 , in the ferroelectric phases, the reflectivity changes are proportional to the applied terahertz electric fields; moreover, the second-order-nonlinear optical responses were observed 16,39 . However, similar responses, as well as SHG, are not observed in κ-Cl down to 10 K. This indicates that the inversion symmetry continues to exist at a macroscopic scale below 40 K.…”

“…The electric fields of both pulses were parallel to the c-axis. In the terahertz-pump optical-reflectivity-probe measurements, we change the electric fields of the terahertz pulses by using two wire-grid polarizers 39,43 .…”

Anisotropic Magnetoelectric Coupling and Cotton–Mouton Effects in the Organic Magnetic Charge-Transfer Complex Pyrene–F4TCNQ

“…The ferromagnetic phase transition and polarization switching in organic systems can only be realized at a low Curie temperature (T c ), for example, 16 K for tetrakis(dimethylamino)ethylene−C 60 (TDAE−C 60 ) 6,7 and 53 K for tetrathiafulvalene-p-bromanil (TTF−BA). 8,9 Thus, it is extremely challenging to realize simultaneous room-temperature dipoles and spin order in organic systems. 10−13 Generally, in organic CT complexes, the donor and acceptor components can be stabilized through noncovalent bonding interactions.…”

Ultrafast polarization switching of (BaSr)TiO3 thin film by a single-period terahertz pulse in a vicinity of phase transition

“…Electric filed can be applied to ferroelectric material in a contact-free fashion using freely propagating nearly single cycle THz pulse. The detection of the pulse-induced changes can be carried out by optical [4,5] or by X-Ray diffraction techniques [6,7]. In optical detection, time domain reflectivity (transmission) or polarization rotation are studied.…”