Berlin 2005 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 15: Superconductivity - Properties, Electronic Structure, Order Parameter I

TT 15.7: Vortrag

Samstag, 5. März 2005, 15:45–16:00, TU H2053

Scanning tunneling spectroscopy on (100) plane of NdBa₂Cu₃O_7−δ — •Pintu Das¹, Michael R. Koblischka¹, Thomas Wolf², Uwe Hartmann¹, and Iduru Shigeta³ — ¹Institute of Experimental physics, University of Saarbruecken, P.O.Box- 151150, D-66041 Saarbruecken, Germany — ²Forschungszentrum Karlsruhe GmbH, Institute of Solid State Physics, D-76021, Karlsruhe Germany — ³Department of General Education, Kumamoto National College of Technology, Kumamoto 861-1102, Japan

We report the results of STS experiments performed on the (100) plane of NdBa₂Cu₃O_7−δ (NdBCO) single crystals (T_c = 95.5 K) at 4.2 K. From the dI/dV curves, which represents the local density of states (LDOS), we find a V-shaped curve with a very high conductance at the zero bias in the gap region which is typical in case of d-wave symmetry of the order parameter. In a region of 200 Å, we also observed other curves with very low coherence peaks or even with no peak structure, which is possible if the oxygen content is inhomogeneously distributed across the surface. A third type of curve, which is not frequently observed, has a peak at the zero bias conductance (ZBCP). We consider that the ZBCP is due to the Andreev reflection at the impurity potential (geometrically rough surface) and can be explained with the theory of roughness effect on the density of states of d-wave superconductor [1]. We can explain the data considering the symmetry order parameter to be d_x²−y² wave, but at this moment we can not confirm if there is a mixing of any other component.

[1] Tanuma et al., Phys. Rev. B57, 7997 (1998).