Ferroelectric nature and real-space observations of domain motions in the organic charge-transfer compound tetrathiafulvalene-p-chloranil

Abstract

Ferroelectricity in an organic charge-transfer compound, tetrathiafulvalene-p-chloranil ͑TTF-CA͒, originating from the one-dimensional valence and lattice instabilities, has been investigated by an electroreflectance ͑ER͒ method. Microscopic ER spectroscopy in the visible region enables real-space observations of both ferroelectric domain structures with a few hundred micrometers in size and depinning of the domain walls under strong electric fields. In addition, from ER spectroscopy in the infrared molecular-vibration region, we demonstrate that field-induced changes in the dimeric molecular displacement as well as charge transfer between TTF and CA molecules play an important role in the large dielectric response in TTF-CA.

Ionic versus Electronic Ferroelectricity in Donor–Acceptor Molecular Sequences

“…This unusual behavior is emphasized in the vicinity of the NIT and consistent with the findings of electroreflectance spectroscopy 45 as well as theoretical studies: 47 both the ionicity μ and intermolecular covalency within the DA dimer increase with the degree of dimerization (and also with the strength of the applied electric field).…”

“…10 8 ³ cm, even at low temperatures around T c ). 44 As evidence of the ferroelectricity on a mesoscopic scale, Kishida et al 45 found coexisting domains of different polarities in TTFCA through microscopic electro-reflectance spectroscopy. The bulk ferroelectric polarization of TTFQBrCl 3 was later evaluated, which showed better insulating properties (ca.…”

Magnetic ordering and charge dynamics in κ-(BEDT-TTF)2Cu[N(CN)2]Cl

“…It is worth recalling the discussion of the neutral-ionic transition in TTF-CA, where the increase of the dielectric constant is associated with domain walls [38]. The domains extend over a few hundred micrometers [39].…”

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

“…THz-field-induced changes in the reflectivity of these probe pulses and the SHG intensity were measured using a boxcar integrator. The diameter of the probe pulse was B200 mm, which is comparable to or smaller than the typical size of ferroelectric domains in TTF-CA 15 . Therefore, by selecting an appropriate measured area on a single crystal, the dynamics of a single ferroelectric domain could be detected.…”

“…In addition, the dimeric molecular displacements are three-dimensionally ordered in phase 13 , yielding in ferroelectricity 14,15 .…”