Berlin 2008 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 18: Correlated Electrons: Low-dimensional Systems - Materials 2
TT 18.1: Vortrag
Dienstag, 26. Februar 2008, 15:15–15:30, H 2053
Charge Ordering in (TMTTF)2X: Evidences for Structural Changes — •Mariano de Souza1, Alec Moradpour2, Pascale Foury2, Jean-Paul Pouget2, and Michael Lang1 — 1Physikalisches Institut, J.W. Goethe-Universität, Max-von-Laue Str. 1, SFB/TRR49, D-60438 Frankfurt am Main, Germany — 2Laboratoire de Physique des Solides, Université Paris Sud, CNRS, UMR 8502, 91405 Orsay, France
The (TMTTF)2X family of quasi-1D organic conductors has been the subject of intensive studies over the last two decades. Recently, NMR spectroscopy studies [1] revealed the existence of a charge-ordered (CO) phase in the X=PF6 and AsP6 salts at TCO≈65 and 105 K, respectively. Until now, however, no evidence of structural changes has been reported in the literature and, due to this, the latter has been referred to as a “structureless" phase transition. In this contribution, we present directional-dependent high-resolution thermal expansion measurements on the X=PF6 salt. Our findings reveal strong anisotropic lattice effects at both the Spin-Peierls and the CO transition, with the strongest response along the c*-axis, along which the stacks are separated by the PF6− anions and where the transfer integral tc* is very weak. For the chain direction (a-axis), less pronounced signatures are observed. These results provide the first evidence for structural effects at the CO transition, indicating both charge and lattice degrees of freedom are involved in this transition.
[1] D.S. Chow et al., Phys. Rev. Lett. 85, 1698 (2000).