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TT: Fachverband Tiefe Temperaturen

TT 18: Correlated Electrons: Low-dimensional Systems - Materials 2

TT 18.9: Vortrag

Dienstag, 26. Februar 2008, 17:30–17:45, H 2053

Competing exchange interactions in the edge-shared chain cuprates CuCl₂ and CuBr₂ — •Miriam Schmitt¹, Stefan-Ludwig Drechsler², and Helge Rosner¹ — ¹MPI CPfS Dresden, Nöthnitzer Strasse 40, D-01187 Dresden — ²IFW Dresden, P.O.Box 270116, D-01171 Dresden

Low dimensional spin 1/2 chain systems show fascinating phase diagrams with many unusual magnetic ground states as spin-Peierls, spin gap or helically ordered states. These ground states are usually driven by the strong competition between the nearest and next nearest neighbor in-chain interactions. We will present a detailed study of the electronic and magnetic properties based on density functional calculation for the edge shared chain Cu²⁺ compounds CuCl₂ and CuBr₂. Starting from LDA band structure calculation we developed an effective one-band tight-binding model and mapped it subsequently to a Heisenberg model to evaluate the orbitals and main interactions relevant for the low energy properties. The combination of these results with the exchange integrals from LDA+U total energy differences of different spin configurations leads to reliable microscopic models. For CuCl₂ and CuBr₂ we find a strong frustration due to competing antiferromagnetic J₂ and ferromagnetic J₁. Unless the significant inter-chain coupling stabilizes a commensurate ground state we predict that both compounds exhibit a helically ordered state at low temperatures.