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Transport in Dense Systems of Almost Localized Electrons near Charge and Spin Ordering

The problem of localized charge carriers transport has been heavily reserached in the limit of their low concentration. The aim of this work is to consider the high concentration limit when the situation is further complicated by non- vanishing interaction between carriers and their ability to create the charge and/or spin ordered states. One example of such a system is the recently described organic kagome material (EDT- TTF-CONH2)6 [Re6Se8(CN)6] [1, 2]. The formation of its ground state is interesting as well, because of the kagome lattice symmetry and the phenomenon of spin frustration. The numeric calculation of transport coefficients is done by implementing the Mahan's lattice-gass formalisam [3, 4] for the Blume-Emery-Griffiths model with two parameters (short-range Coulomb interaction V and spin interaction J). The temperature and concentration dependence of transport coefficients (electric conductivity and thermopower) is examined. We have reproduced the experimentally observed metal-semiconductor soft crossover in resistivity, as well as the dependence of the Seebeck coefficient on temperature. The sharp minimum in the concentration dependence of electrical conductivity appears as the consequence of charge ordering. [1] S. A. Baudron et al., J. Am. Chem. Soc. 123 (33), 11785-11797 (2005). [2] A. Olariu et al. (preprint). [3] J. F. Kwak and G. Beni, Phys. Rev. B 13, 2 (1976). [4] G. D. Mahan, Phys. Rev. B 14, 2 (1976).

polaron gas ; charge ordering ; spin ordering ; thermoelectric power

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