NQR study of neutral–ionic phase transition and quantum paraelectric state in organic charge-transfer complexes

Abstract

NQR measurements were performed for the charge-transfer complexes DMTTF–QBr n Cl n −4 under ambient and hydrostatic pressures in order to understand the neutral–ionic phase transition and the quantum critical behavior. The 35Cl NQR spectrum of DMTTF–QCl 4 showed a splitting and a shift below T c, indicating the occurrence of dimerization and charge transfer. The spin-lattice relaxation rate 1/ T 1 showed a peak anomaly around T c, reflecting the critical slowing down. The quantum paraelectric states in DMTTF–2,6-QBr 2Cl 2 and pressured DMTTF–QBr 4 were studied by the 79Br NQR. We found the microscopic evidence for the evolution of the critical fluctuations at low temperatures in the temperature dependence of spin-lattice relaxation rate.