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Observation of a common symmetry for the pseudogap and the superconducting order parameter near the surface of underdoped YBCO

G. Koren, L. Shkedy, E. Polturak

cond-mat.supr-conarXiv:cond-mat/0306594

Abstract

Measurements of the angular dependence of conductance spectra in the a-b plane of underdoped YBCO junctions are reported. At zero magnetic field the superconducting gap shows a |d+is|-like symmetry. Application of a magnetic field strongly suppresses this gap leaving only the pseudogap feature which also shows a |d+is|-like angular dependence. We thus observe the same symmetry for the superconducting gap and the pseudogap characterizing the YBCO electrodes near the interface with the barrier. An Hc2 value of about 5T of the secondary (is) order parameter can also be deduced from our results.

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