Surface topographic and spectroscopic studies of charge ordering La0.5Sr1.5MnO4 using scanning tunneling microscopy

We have studied the compound La0.5Sr1.5MnO4 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 TCO∼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>TCO and TTCO and the opening of a gap Δ∼0.5 eV just below TCO. 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