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TT: Tiefe Temperaturen

TT 19: Metall-Isolator-Überg
änge, Phasenüberg
änge in Quantensystemen II

TT 19.1: Hauptvortrag

Donnerstag, 14. März 2002, 09:30–10:00, H20

Spin-orbital fluctuations in the insulating and conducting phases of BaVS₃ — •Patrik Fazekas — Research Institute for Solid State Physics and Optics, Budapest, Hungary

We studied the pressure (p) and magnetic field (H) dependence of the electrical, magnetic, and optical properties of BaVS₃. A peculiar crystal structure and crystal field scheme make BaVS₃ unique among correlated 3d systems. A surface of metal-insulator transitions (MIT) separates the low-T non-magnetic spin-gapped insulator from high-T bad metallic states. The character of the MIT is debated. At low p and H, the MIT is continuous, implying that the spin gap is sustained by a spin-orbital order which is, however, different from either conventional magnetic order or dimerization. Thermopower (TEP) suggests a change in the character of the transition at p>7.5kbar. The spin and the charge gap are suppressed by either p or H, vanishing at a critical pressure (or field). In the conducting phase, a low-p pseudogap regime is indicated by a resistivity precursor and a TEP anomaly. The high-p metal is non-Fermi liquid.

The anomalous metallic and insulating states, and the MIT itself, are explicable by the mutual frustration of orbital and spin interactions, and the interplay of spin-orbital fluctuations with atomic dynamics.

Thanks to: N. Barisic, H. Berger, L. Forró, R. Gaál (Lausanne, Switzerland); Sz. Csonka, I. Kézsmárki, G. Mihály, K. Penc (Budapest, Hungary).