Exploring the Charge-Ordering Transition in (TMTTF)${}_2$X via Thermal Expansion Measurements

Abstract

We report results of high-resolution measurements of the \emph{c${}^{\ast }$}-axis expansivity (${\alpha }_{c^{\ast }}$) at the charge-ordering (CO) transition for the quasi-1D (TMTTF)${}_2$X compounds with X = SbF${}_6$ and Br and make a comparison with previous results for the X = PF${}_6$ and AsF${}_6$ salts. For X = SbF${}_6$, due to the screening of the long-range Coulomb forces, a sharp $\lambda$-type anomaly is observed at $T_{CO}$, which contrasts with the step-like 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 ${\alpha }_{c^{\ast }}$ is observed above $T_{CO}$. This feature is assigned to the anions' rigid-unit modes, which become inactive for $T$ $<$ $T_{CO}$. Our ${\alpha }_{c^{\ast }}$ results for the X = 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 = PF${}_6$ and AsF${}_6$ salts.

Submitted to Special Issue - ISCOM 2009 - Physica B Condensed Matter

References in corpus (6)

• The ferroelectric Mott-Hubbard phase of organic (TMTTF)2X conductors
• Electron-lattice coupling and the broken symmetries of the molecular salt (TMTTF)${}_2$SbF${}_6$
• Ordering phenomena in quasi one-dimensional organic conductors
• Anomalous Lattice Response at the Mott Transition in a Quasi-2D Organic Conductor
• Evidence for Lattice Effects at the Charge-Ordering Transition in (TMTTF)${}_2$X
• Influence of the anion potential on the charge ordering in quasi-one dimensional charge transfer salts

Cited by in corpus (6)

• Electronic crystals: an experimental overview
• Comprehensive transport studies of anisotropy and ordering phenomena in quasi-one-dimensional (TMTTF)2X salts (X = PF6, AsF6, SbF6; BF4, ClO4, ReO4)
• Charge-Ordering Transition in (TMTTF)${}_2$X Explored via Dilatometry
• Probing the Mott Physics in $\kappa$-(BEDT-TTF)${}_2$X Salts via Thermal Expansion
• Low temperature structural effects in the (TMTSF)${}_2$PF${}_6$ and AsF${}_6$ Bechgaard salts
• Superlattice Induced by Charge Order in the Organic Spin Chain (TMTTF)${}_{2}X$ ($X=$ SbF${}_6$, AsF${}_6$ and PF${}_6$) Revealed by High Field EPR