Electromodulation spectroscopy in ferroelectric CT complex: TTF-CA

Electroreflectance spectra have been measured on the ionic phase of a mixed-stack charge-transfer (CT) complex, TTF-CA, in a frequency range from 100Hz to 7kHz. We detect two types of electroreflectance signals in a visible region; one has the same frequency (=1f) as the applied electric field and another has the doubled frequency (=2f). The analysis of the spectral shape reveals that both signals come from the modulation of the degree of CT. The activation of the If and 2f components is related to the broken symmetry of the ground state induced by the dimerization along 1D chains and the field-induced motion of domain walls, respectively.