Microwave dielectric study of spin-Peierls and charge ordering transitions in (TMTTF)$_2$PF$_6$ salts

TL;DR

This study investigates the dielectric properties of (TMTTF)$_2$PF$_6$ salts, revealing insights into charge ordering, spin-Peierls transitions, and the effects of hydrogenation and deuteration on these phenomena.

Contribution

It provides new experimental data on dielectric behavior and phase transitions in (TMTTF)$_2$PF$_6$ salts, highlighting the influence of isotopic substitution and magnetic fields.

Findings

Charge ordering transition shows relaxor behavior in dielectric response.

Deuteration increases charge ordering temperature by over 30%.

Spin-Peierls transition exhibits anomalies indicating lattice effects.

Abstract

We report a study of the 16.5 GHz dielectric function of hydrogenated and deuterated organic salts (TMTTF)$_2$PF$_6$. The temperature behavior of the dielectric function is consistent with short-range polar order whose relaxation time decreases rapidly below the charge ordering temperature. If this transition has more a relaxor character in the hydrogenated salt, charge ordering is strengthened in the deuterated one where the transition temperature has increased by more than thirty percent. Anomalies in the dielectric function are also observed in the spin-Peierls ground state revealing some intricate lattice effects in a temperature range where both phases coexist. The variation of the spin-Peierls ordering temperature under magnetic field appears to follow a mean-field prediction despite the presence of spin-Peierls fluctuations over a very wide temperature range in the charge ordered state of these salts.