Dresden 2006 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 19: Correlated Electrons: Low-dimensional Materials
TT 19.19: Vortrag
Dienstag, 28. März 2006, 18:45–19:00, HSZ 301
Infrared and Raman studies of the competition between spin and charge order in quasi-1D conductors — •Michael Dumm1, Matteo Masino2, and Martin Dressel1 — 11. Physikalisches Institut, Universität Stuttgart, Stuttgart, Germany — 2Dipartimento di Chimica and INSTM-UdR, Università di Parma, Parma, Italy
Charge order (CO) phenomena and their competition with spin order are one focus of recent research on low-dimensional highly correlated materials like organic conductors or transition-metal oxides. In the quasi-1D (TMTTF)2X charge-transfer salts charge disproportionation (CD) on the (TMTTF)2-dimers leads to a ferroelectric CO state. Subsequently, at lower T a transition into a spin-Peierls ground state is observed. Up to now, issues like the charge-order patterns and the coexistence of charge- and spin-ordered ground states in this class of materials remain unclear. We address these issues with T-dependent polarized infrared and Raman spectroscopy on single crystals of (TMTTF)2X.
In the mid-IR spectra, we observed a splitting of several vibronic modes below the charge-order transition which can be directly linked to the CD on the molecules. At far-IR frequencies below 100 cm−1, new intradimer vibrations get IR active along all three crystal axes in the CO state due to the unequal charge distribution on the TMTTF molecules. Above the CO transition, these modes are Raman active. We performed a detailed analysis of the temperature dependence of these modes. We find for the first time clear evidence that the charge order coexists with the spin-Peierls ground state at low temperatures despite the fact that both are competing ground states.