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TT: Tiefe Temperaturen

TT 12: Correlated Electrons: Low-dimensional Systems - Models

TT 12.8: Vortrag

Dienstag, 28. März 2006, 11:30–11:45, HSZ 304

Charge Response in Quasi-1D Wigner Lattice Systems — •Anup Mishra¹, Matthias Mayr², and Peter Horsch¹ — ¹Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany. — ²Dept. of Physics, Univ. of Tennesse, Knoxville, USA

Doped edge-sharing Cu-O chain compounds are ideal realizations of 1D Wigner lattices(WL). Such chains are found in the recently synthesized Na₃Cu₂O₄ and Na₈Cu₅O₁₀ systems [1] and are also structural elements in the composite compound Sr_14−xCa_xCu₂₄O₄₁. As a result of the structure the hopping matrix elements t_l and hence the kinetic energy are small compared to the Coulomb energy. At low temperature the charge order resulting from Coulomb interaction V_l ∼ V/l generates modulated Heisenberg chains with varying distance between spins. We discuss the charge dynamics of WL starting from a model of spinless fermions. We give a detailed discussion of domain-wall excitation spectra and excitonic states at doping x=1/2. In the model with t₁ only the resulting periodicity of WL charge modulation may also be explained by a 4k_F charge-density wave(CDW) arising from a Fermi surface instability. However due to the ≈ 90^∘ Cu-O-Cu bond angle in edge-sharing chains |t₂|>|t₁|. Presence of t₂ does not affect the classical WL order, but it changes the Fermi surface topology. This allows to distinguish the WL from the CDW on the basis of the modulation period. We present a detailed phase diagram taking into account t₁, t₂ and V_l. [1] P. Horsch, M. Sofin, M. Mayr, and M. Jansen, Phys. Rev. Lett. 94, 076403 (2005).