Phase Diagram of Fabre Salts

By Tom Sharp on February 13, 2017

Organic charge transfer salts are a hot topic within the condensed matter community. In a recent Journal of Physics: Condensed Matter paper, Martin Dressel et al. investigated tetramethyltetrathiafulvalene (TMTTF) Fabre salts using vibrational spectroscopy. Read on to find out more in the authors’ words:

The charge-ordered ground state of one-dimensional TMTTF-salts is mainly driven by electronic correlations that can be tuned effectively by applying hydrostatic pressure. Infrared spectroscopy of molecular vibrations is a powerful tool for quantitatively investigating the local charge per molecule. In our recent paper we investigate the temperature and pressure dependence of (TMTTF)₂SbF₆, (TMTTF)₂AsF₆ and (TMTTF)₂PF₆ for a wide range.

Phase diagram obtained by pressure- and temperature-dependent infrared measurements of (TMTTF)2AsF6 and (TMTTF)2SbF6 single crystals. Image taken from J. Phys. Cond. Mat. 29 115601 © Copyright 2017 IOP Publishing

We find that charge order and the Spin Peierls ground state coexist with a maximum T_SP right where charge order is suppressed, indicating the competition of the two phases. Following the variation of the methylene group and the anion vibrations with pressure and temperature, we elucidate the coupling of the counterions to the molecular stack, the involvement of the anions in the charge order, and spin-Peierls transition. Presumably, the stability of these states depends on the amount of translational freedom the anions experience within the cavity.

We will continue our investigations with measurements of Fabre salts with non-centrosymmetric anions, in order to explore the influence of anion order.

The 1. Physikalisches Institut, Universität Stuttgart, Germany, headed by Professor Martin Dressel, focuses on the electronic and magnetic properties of low-dimensional electron systems. The group is renowned for its investigations on the electrodynamics of electronically correlated matter, in particular organic conductors and superconductors.

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