Regensburg 2010 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 27: CE: Poster Session
TT 27.2: Poster
Wednesday, March 24, 2010, 14:00–18:00, Poster D1
Dilatometric Investigations at the Charge-Ordering Transition in (TMTTF)2X — •Daniel Hofmann1, Mariano de Souza1, Christian Balz1, P. Foury-Leylekian2, A. Moradpour2, J.-P. Pouget2, and Michael Lang1 — 1Physikalisches Institut, Goethe-Universität, Max-von-Laue Str. 1, SFB/TR49 D-60438 Frankfurt (M), Germany — 2Laboratoire de Physique des Solides, Université Paris Sud, CNRS UMR 8502, Orsay, France
We report results of high-resolution measurements of the c*-axis expansivity (αc*) at the charge-ordering (CO) transition for the quasi-1D (TMTTF)2X compounds with X = Br and SbF6 and make a comparison with previous results for the X = PF6 and AsF6 salts [1]. For X = SbF6, due to the screening of the long-range Coulomb forces, a sharp λ-type anomaly is observed at TCO, which contrasts with the step-like mean-field anomaly at TCO for PF6 and AsF6, where CO occurs in the Mott-Hubbard charge-localized regime. For the latter two salts, a negative contribution to αc* is observed above TCO. This effect is assigned to the anions’ rigid-unit modes, which become inactive for T < TCO. Measurements for the X = Br salt, where such rigid-unit modes are absent, reveal no traces of such negative contribution to αc*, confirming the model based on the anions’ rigid-unit modes for the X = PF6 and AsF6 salts [1].
[1] M. de Souza et al., Phys. Rev. Lett. 101, 216403 (2008).