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TT: Fachverband Tiefe Temperaturen

TT 32: Correlated Electrons: Poster Session

TT 32.34: Poster

Donnerstag, 28. Februar 2008, 14:00–18:00, Poster B

Surface topographic and spectroscopic studies of charge ordering La_0.5Sr_1.5MnO₄ using Scanning Tunneling Microscopy — •Paul Sass¹, Grzegorz Urbanik^1,2, Christian Hess¹, Torben Hänke¹, Bernd Büchner¹, Antoni Ciszewski², Pascal Reutler³, and Alexandre Revcolevschi³ — ¹Institute for Solid State Research, IFW-Dresden, 01171 Dresden, Germany — ²Institute of Experimental Physics, University of Wroclaw, 50-204 Wroclaw, Poland — ³Laboratoire de Physico-Chimie de l’Etat Solide, Université Paris Sud, Bâtiment 414, 91405 Orsay, France

We have studied the compound La_0.5Sr_1.5MnO₄ which can be considered as a textbook example of charge and orbital ordering by means of Scanning Tunneling Microscopy (STM) and Spectroscopy (STS). We were able to cleave the material in-situ under Ultra High Vacuum conditions prior to the STM/STS studies. Topographic scans routinely reveal atomically resolved surfaces both above and below the charge ordering temperature T_CO≈225 K (down to T≈ 205 K). The step height analysis suggests cleaving between the (Sr,La)O-layers. We have studied the temperature dependence of the electronic structure both for T>T_CO and T<T_CO. The STS clearly reveals finite DOS at the Fermi level for T>T_CO and the opening of a gap Δ≈0.5 eV just below T_CO. In the topographic studies we find nanometer scale modulations with various periodicity. We discuss these modulations in view of the inherent charge and orbital ordered state of this material. We compare our results with STS studies on other transition metal oxides exhibiting inhomogeneous charge distributions.