Dresden 2009 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 6: Postersession Correlated Electrons: (General) Theory, Low-Dimensional Systems, Kondo Physics, Heavy Fermions, Quantum-Critical Phenomena
TT 6.68: Poster
Montag, 23. März 2009, 13:00–16:45, P1A
Quantum criticality in the quasi one-dimensional Ising spin-1/2 chain system BaCo2V2O8 — •Sandra Niesen, Martin Valldor, Oliver Heyer, and Thomas Lorenz — II. Physikalisches Institut, Universität zu Köln, Germany
BaCo2V2O8 contains screw chains of CoO6 octahedra which are running along the c axis of the tetragonal crystal structure and are separated by nonmagnetic Ba2+ und V5+ ions in the aa plane. Due to a compression of the octahedra along c the threefold degeneracy of the t2g orbitals is lifted and the magnetic ground state can be described by an effective Ising spin-1/2 antiferromagnetic chain. In zero magnetic field BaCo2V2O8 shows long-range antiferromagnetic order below TN≃ 5.5 K with the spins oriented along c. The magnetic field influence is highly anisotropic. For magnetic fields applied in the aa plane TN is only weakly suppressed, e.g. TN≃ 4.5 K for H=8 T. In case of H parallel c, however, the Néel order is completely suppressed already for fields above about 4 T. Thus, BaCo2V2O8 is ideally suited to study this field-induced quantum phase transition. We have prepared single crystals of BaCo2V2O8 by a spontaneous nucleation method and have performed measurements of the magnetization, the specific heat, the thermal expansion, and the magnetostriction. These results will be compared to existing theory.
This work is supported by the DFG through SFB 608.