Berlin 2005 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 2: Correlated Electrons - Metal Insulator Transition

TT 2.11: Vortrag

Freitag, 4. März 2005, 12:45–13:00, TU H2053

Effect of pressure on the electric transport properties of RNiO₃ — •R. Lengsdorf¹, J.A. Alonso², D.I. Khomskii¹, H. Micklitz¹, and M.M. Abd-Elmeguid¹ — ¹II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln — ²Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, E-28049 Madrid, Spain

The temperature-induced metal-insulator (MI) transition in the RNiO₃ series has been ascribed to an opening of a small charge transfer gap at T<T_MI which is intimately connected with either a slight but abrupt expansion of the unit cell volume or an orthorhombic (Pbnm) to monoclinic (P2_1/n) structural transition for large (R=Pr,.., Eu) and small (R=Dy,.., Lu) R³⁺ ions, respectively. The monoclinic symmetry in the insulating state implies two independent Ni-sites and the presence of charge ordering. Experimental evidence for such a charge ordered state in larger R³⁺ nickelates has recently been reported (e.g. EuNiO₃ and NdNiO₃ thin films), supporting the importance of charge ordering for the occurence of the temperature-induced MI transition. For a deeper understanding of the mechanism of the MI transition in the RNiO₃ series, we have studied the effect of pressure on the transport properties of some selected RNiO₃ (R=Sm, Eu, Y and Lu) oxides. While the monoclinic structure of YNiO₃ (T_MI=582 K and T_N=138 K) and LuNiO₃ (T_MI=599 K and T_N=125 K) remains stable up to 14 GPa and 16 GPa, respectively, the pressure-temperature dependence of the electrical resistance clearly indicates a transition to a metallic state already at p≥5 GPa. Possible mechanisms responsible for the pressure-induced insulator-metal transition in RNiO₃ series will be discussed.