Regensburg 2007 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 8: Superconductivity - Poster Session

TT 8.7: Poster

Monday, March 26, 2007, 14:00–17:45, Poster A

Surface studies of underdoped YBa₂Cu₃O_6.6 by means of Scanning Tunneling Microscopy — •Grzegorz Urbanik^1,2, Torben Hänke¹, Christian Hess¹, Bernd Büchner¹, Antoni Ciszewski², Vladimir Hinkov³, and Chengtian Lin³ — ¹Leibniz-Institute for Solid State and Materials Research, IFW-Dresden, 01171 Dresden, Germany — ²Institute of Experimental Physics, University of Wroclaw, Poland — ³Max Planck Institute for Solid State Research, Heisenbergstrae 1, D-70569 Stuttgart, Germany

According to the data in the literature, low temperature (<40 K) cleaving of YBa₂Cu₃O_7−δ-single crystals under UHV conditions (in order to get high quality surfaces), leads mainly to either BaO or CuO sheets as the topmost layer. We performed scanning tunneling microscopy and spectroscopy on high quality underdoped YBa₂Cu₃O_6.6 crystals. We present topographic results and a detailed statistical analysis of the step heights on a micrometer scale. Our data show that the cleaving of this material below 40K is much more complicated than anticipated. We find that the material primarily cleaves in multiples of one unit cell. Fractional step heights are also found, but only in few cases (∼5%). The topmost layers often exhibit a high corrugation (∼3 Å) which indicates that cleaving takes place at either the CuO chain layer or the Y-layer involving a non-uniform distribution of the layer atoms on the two cleaving planes. Furthermore, scanning tunneling spectroscopy reveals that terraces with a height difference smaller than one unit cell differ significantly in their tunneling conductance.