Exploring the charge-ordering transition in via thermal expansion measurements

✍ Scribed by Mariano de Souza; Daniel Hofmann; Pascale Foury-Leylekian; Alec Moradpour; Jean-Paul Pouget; Michael Lang

• Publisher: Elsevier Science
• Year: 2010
• Tongue: English
• Weight: 227 KB
• Volume: 405
• Category: Article
• ISSN: 0921-4526
• DOI: 10.1016/j.physb.2009.12.022

✦ Synopsis

We report results of high-resolution measurements of the c à -axis expansivity (a c Ã) at the chargeordering (CO) transition for the quasi-1D ðTMTTFÞ 2 X compounds with X ¼ SbF 6 and Br and make a comparison with previous results for the X ¼ PF 6 and AsF 6 salts. For X ¼ SbF 6 , due to the screening of the long-range Coulomb forces, a sharp l-type anomaly is observed at T CO , which contrasts with the steplike mean-field anomaly at T CO for PF 6 and AsF 6 , where CO occurs in the Mott-Hubbard charge-localized regime. For the latter two salts, a negative contribution to a c à is observed above T CO . This feature is assigned to the anions' rigid-unit modes, which become inactive for T o T CO . Our a c à results for the X ¼ Br salt, where such rigid-unit modes are absent, reveal no traces of such negative contribution, confirming the model based on the anions' rigid-unit modes for the X ¼ PF 6 and AsF 6 salts.