Regensburg 2010 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 11: CE: Low-dimensional Systems - Materials 2

TT 11.7: Vortrag

Dienstag, 23. März 2010, 11:15–11:30, H18

Spectroscopic ellipsometry study of the edge-sharing CuO₄ chain cuprate Li₂CuO₂ — •Yulia Matiks¹, A.V. Boris¹, J. Malek², S. Nishimoto², S.-L. Drechsler², P. Horsch¹, N. Wizent², G. Behr², M. Knupfer², B. Buchner², and B. Keimer¹ — ¹Max-Planck-Inst. f. Festkörperforschung, Stuttgart, Germany — ²Leibniz-Inst. f. Festkörper- & Werkstoffforschung, Dresden, Germany

Motivated by observation of a double-peak structure in the edge-sharing chain cuprate LiCuVO₄, assigned to the Zhang-Rice exciton states [1], we report detailed ellipsometric measurements on Li₂CuO₂. This compound is characterized by different ratio between the near-neighbor J₁ and the next-near-neighbor J₂ exchange integrals, α = − J₂/ J₁=0.33 [2]. Temperature dependence of the interband transition peaked at 3.7 eV in the optical conductivity along the chains follows spin correlations and becomes apparent below T_N ≈ 9 K. This excitation is assigned to the Zhang-Rice singlet excitation and modelled within a five band Cu 3d O2 p extended Hubbard model including long range Coulomb interactions. Applying exact diagonalization and DMRG studies to Cu_nO_2n+2 chains and corresponding rings a strong intersite Coulomb interaction of about V_pd=2.2 eV is found. The main in-chain exchange integrals obtained from a mapping onto a spin-1/2 Hamiltonian are in agreement with the spin wave analysis of the new detailed inelastic neutron scattering study [2].

[1] Y. Matiks et al., Phys. Rev. Lett. 103, 187401 (2009).

[2] W.E.A. Lorenz et al., Europhys. Lett. 88, 37002 (2009).