Decoupled critical dynamics of the TMTSF donor molecules in (TMTSF)_2X organic superconductors

摘要

We have studied a high-temperature phase transition in the organic superconductors (TMTSF)_2PF_6 and (TMTSF)_2ClO_4 (where TMTSF indicates tetramethyltetraselenafulvalene) by means of ~1H laboratory-frame and rotating-frame nuclear magnetic resonance (NMR) relaxation measurements. The ~1H NMR spin-lattice (T_1) and spin-spin relaxation time (T_2), representing dynamics of the TMTSF donor molecules, manifested a divergence associated with the structural phase transition at 160 K. As no anomalies were observed in the ~(19)F NMR T_1 measurements representing dynamics of the PF_6 anion, the TMTSF donor molecules and the anions are shown to be well decoupled regarding the critical fluctuations accompanying the structural phase transition.