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TT: Fachverband Tiefe Temperaturen

TT 16: Correlated Electrons: Low-dimensional Systems - Materials 1

TT 16.7: Vortrag

Dienstag, 24. März 2009, 11:00–11:15, HSZ 304

Electronic structure and exchange coupling of a frustrated S=1/2 pyrochlore Hg₂Cu₂F₆S — •Deepa Kasinathan¹, Klaus Koepernik², and Helge Rosner¹ — ¹Max Planck Institute for Chemical Physics of Solids, Dresden, Germany — ²Leibniz Institute for Solid State and Materials Research Dresden, Germany

Spin systems with geometric frustration have a macroscopic number of degenerate low lying states. An interesting question to answer for such kind of systems is: "Which state is chosen as the ground state at low T?" Our talk will focus on the pyrochlore compound Hg₂Cu₂F₆S which exibits a perfectly cubic CuF₆ octahedral environment.[1] This is quite unusual for a Cu²⁺ ion which is normally in the 4+2 coordination. The lack of distortion for the CuF₆ octahedron leads to a 2-fold degenerate e_g band complex at the Fermi level. Since the system is insulating due to the presence of strong Coulomb repulsion, this 2-fold degeneracy is strongly disfavoured because it would lead to metallicity. Orbital or charge ordering can lift this degeneracy. Strong magnetic frustrations will also play a role in determining the ground state of this system due to the presence of 3D linkages of corner sharing Cu₄ tetrahedra. We will present results from density functional theory (DFT) calculations within the LDA and LDA+U methodology. We will discuss the role of total energies, hoppings and possible orbital ordering (visible in the spin density) in this compound.

[1]. S. Kawabata et al., J. Phys. Soc. Japan Vol 76, No.8, 084705 (2007).