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Dresden 2009 – scientific programme

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TT: Fachverband Tiefe Temperaturen

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

TT 16.7: Talk

Tuesday, March 24, 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 Rosner11Max 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 eg 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).

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