Decoupled critical dynamics of the TMTSF donor molecules in (TMTSF) 2 X organic superconductors

Abstract

We have studied a high-temperature phase transition in the organic superconductors (TMTSF) 2 PF6 and (TMTSF) 2 ClO4 (where TMTSF indicates tetramethyltetraselenafulvalene) by means of H1 laboratory-frame and rotating-frame nuclear magnetic resonance (NMR) relaxation measurements. The H1 NMR spin-lattice (T1) and spin-spin relaxation time (T2), 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 F19 NMR T1 measurements representing dynamics of the PF6 anion, the TMTSF donor molecules and the anions are shown to be well decoupled regarding the critical fluctuations accompanying the structural phase transition. © 2006 The American Physical Society.