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TT: Tiefe Temperaturen

TT 6: Niederdimensionale Systeme (incl. Peierls-Übergang, organische Leiter, ...)

TT 6.3: Vortrag

Montag, 8. März 2004, 14:45–15:00, H18

Optical studies of charge ordering in quasi-1D organic conductors — •Michael Dumm, Mohamed Abaker, and Martin Dressel — 1. Physikalisches Institut, Universität Stuttgart, 70550 Stuttgart

Interactions between charge, spin, or lattice degrees of freedom result in the extraordinary rich phase diagram of the quasi-1D (TMTTF)₂X and (TMTSF)₂X charge-transfer salts with ground states like charge order, spin order, anion order, and superconductivity. The focus of this contribution is on the charge-order transition in (TMTTF)₂AsF₆ and (TMTTF)₂PF₆ which is related to charge disproportionation along the molecular stacks at moderate temperatures T_CO. We investigated this phase transition into a ferroelectric state by infrared spectroscopy. For the first time, the lattice dynamics was explored in the vicinity of T_CO. We observed a splitting of the electron-molecular-vibration coupled totally symmetric intramolecular a_g(ν₃) mode in the charge-ordered state. From this result a charge disproportionation on the TMTTF molecular stacks of about 2:1 in (TMTTF)₂AsF₆ and 1.25:1 in (TMTTF)₂PF₆ can be estimated. In the very far infrared spectral range, we found new absorption modes in the optical conductivity below T_CO.