Münster 1999 – scientific programme
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TT: Tiefe Temperaturen
TT 9: Postersitzung I: TT-Teilchendetektoren (1-7), TT-Techniken (8-11), 2-D-Systeme (12-21), Meso- u. nanoskopische Strukturen (22-44), Niederdim. Spinsysteme (45-60), Tunneln u. Symmetrien (61-65), SQUID-Anwendungen (66-73), Massive HTSL, Bandleiter (74-96)
TT 9.47: Poster
Tuesday, March 23, 1999, 09:30–12:30, Z
Optical conductivity of α′-NaV2O5 — •M. Cuoco, P. Horsch, and F. Mack — Max-Planck-Institut fur Festkorperforschung, Heisenbergstr. 1, D-70569 Stuttgart
The physics of low dimensional quantum systems like spin chains, ladders or plaquettes has been receiving considerable interest due to the surprising changes of the ground state and excitation spectrum in the 1D-2D crossover. On the other hand, how the doping modifies the ground state and the excitation spectrum is not well understood until now. In this respect, the vanadate α′-NaV2O5, initially identified as an inorganic spin-Peierls compound similar to CuGeO3, has been attracting great interest as a quarter filled ladder material that displays an intriguing interplay between spin and charge degrees of freedom due to the valence fluctuations of V ions. Using numerical techniques it is shown that the extended t-J model at quarter filling on a trellis lattice is suitable for getting a quantitative explanation of the optical conductivity in the α′-NaV2O5 compound. The combined effects of the short-range Coulomb potential together with the valence fluctuation of V ions on the optical spectra are investigated. We show that the main peak at ∼1 eV observed [1] for an electric field polarized along the a direction is associated with a transition to a bound excited state of pairs of double-domain walls. We have found indications that the low energy features in the a direction of the optical spectra are related to the presence of domain walls in the ground state and to the direct spin-charge coupling induced by the short range Coulomb potential on the electron dynamics. By fitting the experiments we can estimate the values of the microscopic parameters involved, namely the Coulomb repulsion and the hopping matrix elements. [1] A. Damascelli et al.,Phys. Rev. Lett. 81, 918 (1998).