Competition and coexistence of bond and charge orders in (TMTTF)2AsF6

TL;DR

This study investigates the interplay between charge and spin orders in (TMTTF)2AsF6, revealing their competing nature and how external pressure influences their transition temperatures, supported by experimental and theoretical analysis.

Contribution

It provides new insights into the competition between charge-ordering and spin-Peierls transitions in a quasi-one-dimensional organic conductor, combining NMR experiments with theoretical modeling.

Findings

Charge-ordering occurs at 103 K with a 3:1 charge disproportionation.

Pressure suppresses charge-ordering and raises the spin-Peierls transition temperature.

Experimental results align with predictions from the 1D extended Peierls-Hubbard model.

Abstract

(TMTTF)2AsF6 undergoes two phase transitions upon cooling from 300 K. At Tco=103 K a charge-ordering (CO) occurs, and at Tsp(B=9 T)=11 K the material undergoes a spin-Peierls (SP) transition. Within the intermediate, CO phase, the charge disproportionation ratio is found to be at least 3:1 from carbon-13 NMR 1/T1 measurements on spin-labeled samples. Above Tsp, up to about 3Tsp, 1/T1 is independent of temperature, indicative of low-dimensional magnetic correlations. With the application of about 0.15 GPa pressure, Tsp increases substantially, while Tco is rapidly suppressed, demonstrating that the two orders are competing. The experiments are compared to results obtained from calculations on the 1D extended Peierls-Hubbard model.