Berlin 2008 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 15: Superconductivity: Poster Session
TT 15.10: Poster
Dienstag, 26. Februar 2008, 14:00–18:00, Poster B
Energy gap and asymmetry of coherence peaks in 123 cuprate superconductors and their Tc dependence — •Pintu Das1,3, Michael R. Koblischka1, Thomas Wolf2, and Uwe Hartmann1 — 1Institute of Experimental Physics, University of Saarland, 66041, Saarbruecken, Germany — 2Forschungzentrum Karlsruhe GmbH, Institute of Solid State Physics, 76021 Karlsruhe, Germany — 3Max Planck Institute of Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany
The energy gap in conventional superconductors is directly proportional to the transition temperature. In high-Tc cuprate superconductors, scanning tunneling spectroscopy (STS) and angle resolved photoemission studies have often shown that the underdoped samples which have low Tc values exhibit very large energy gaps giving rise to a high value of the coupling ratio (2Δ/kBTc). This has been mostly observed for Bi2Sr2CaCu2O8+δ. In this work, we observe from the STS experiments on NdBa2Cu3O7−δ single crystal samples that the average energy gap increases with the decrease of Tc. For a moderately underdoped sample the coupling ratio is found to be as high as 18. We also observed an asymmetry in coherence peaks which is minimum in the case of optimally doped (highest Tc) samples. The observed Tc dependence of the asymmetry suggests that it is related to the number of electrons and holes.