Neutral–Ionic Phase Transition in DMTTF-QCl₄ Investigated by ³⁵Cl NQR

Abstract

We report a 35 Cl NQR investigation into the neutral–ionic (NI) phase transition in DMTTF-QCl 4 (4,4'-dimethyltetrathiafulvalene- p -chloranil), the end material of the family containing an NI quantum transition system. Four distinct lines with comparable intensities were observed well below T c =65 K; this observation is consistent with the antiferroelectric nature of the ionic phase. The temperature dependences of the spectral shift and splitting below T c are moderate in contrast with the case of TTF-QCl 4 . Low-energy charge-lattice fluctuations are observed around T c as a drastic increase of 1/ T 1 , allowing the observation of the quantum fluctuations in a chemically substituted complex. An analysis of the NQR spectra yields detailed temperature variations in the charge transfer and the concomitant lattice distortion around the NI transition.