# Exploring the Charge-Ordering Transition in TMTTF$2$X via Thermal Expansion Measurements - Condensed Matter > Strongly Correlated Electrons

Exploring the Charge-Ordering Transition in TMTTF$2$X via Thermal Expansion Measurements - Condensed Matter > Strongly Correlated Electrons - Download this document for free, or read online. Document in PDF available to download.

Abstract: We report results of high-resolution measurements of the \emph{c$^*$}-axisexpansivity $\alpha {c^{*}}$ at the charge-ordering CO transition for thequasi-1D TMTTF${2}$X compounds with X = SbF$6$ and Br and make a comparisonwith 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 $\lambda$-typeanomaly is observed at $T {CO}$, which contrasts with the step-like mean-fieldanomaly at $T {CO}$ for PF$6$ and AsF$6$, where CO occurs in the Mott-Hubbardcharge-localized regime. For the latter two salts, a negative contribution to$\alpha {c^{*}}$ is observed above $T {CO}$. This feature is assigned to theanions- rigid-unit modes, which become inactive for $T$ $<$ $T {CO}$. Our$\alpha {c^{*}}$ results for the X = Br salt, where such rigid-unit modes areabsent, reveal no traces of such negative contribution, confirming the modelbased on the anions- rigid-unit modes for the X = PF$6$ and AsF$6$ salts.

Author: Mariano de Souza, Daniel Hofmann, Pascale Foury-Leylekian, Alec Moradpour, Jean-Paul Pouget, Michael Lang

Source: https://arxiv.org/