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

NQR measurements were performed for the charge-transfer complexes DMTTF–QBrnCln−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–QCl4 showed a splitting and a shift below Tc, indicating the occurrence of dimerization and charge transfer. The spin-lattice relaxation rate 1/T1 showed a peak anomaly around Tc, reflecting the critical slowing down. The quantum paraelectric states in DMTTF–2,6-QBr2Cl2 and pressured DMTTF–QBr4 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.

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