Influence of Charge Order on the Ground States of TMTTF Molecular Salts.pdf

Influence of Charge Order on the Ground States of TMTTF Molecular Salts 1 1,2 1 3 3 1 W. Yu , F. Zamborszky , B. Alavi , A. Baur , C. A. Merlic , and S. E. Brown 1Department of Physics, UCLA, Los Angeles, CA 90095 USA 3 2Los Alamos National Laboratory, Los Alamos, NM 87545 USA 0 3 0 Department of Chemistry and Biochemistry, UCLA, Los Angeles, CA 90095 USA 2 c e D Abstract. (TMTTF ) AsF and (TMTTF ) SbF are both known to undergo a charge ordering phase 2 6 2 6 6 transition, though their ground states are different. The ground state of the first is Spin-Peierls, and the 1 second is an antiferromagnet. We study the effect of pressure on the ground states and the charge-ordering 13 using C NMR spectroscopy. The experiments demonstrate that the the CO and SP order parameters are ] l repulsive, and consequently the AF state is stabilized when the CO order parameter is large, as it is for e (TMTTF ) SbF . An extension of the well-known temperature/pressure phase diagram is proposed. - 2 6 r t s. Keywords. Organic conductors, charge order, spin-Peierls, antiferromagnet, high-pressure t a m - 1. INTRODUCTION d n o Unlike the highly-conducting TMTSF analog compounds, molecular salts based on T MT T F molecules c tend to insulating behavior below T = 100 − 300K . It is commonly attributed to a dimerization of the [ T MT T F stacks that results in a half-filled anti-bonding band [1]. A Mott-Hubbard gap results, without 1 additional symmetry breaking, once electronic correlations are included. If the dimerization is sufficiently v 7 weak compared to the interchain hoppi