The European Physical Journal B - Condensed Matter and Complex Systems

, Volume 22, Issue 4, pp 411-414

First online:

Evidence for pseudogap and phase-coherence gap separation by Andreev reflection experiments in Au/ La 2 - x Sr x CuO 4 point-contact junctions

  • R.S. GonnelliAffiliated withINFM - Dipartimento di Fisica, Politecnico di Torino, 10129 Torino, Italy
  • , A. CalzolariAffiliated withINFM - Dipartimento di Fisica, Politecnico di Torino, 10129 Torino, Italy
  • , D. DagheroAffiliated withINFM - Dipartimento di Fisica, Politecnico di Torino, 10129 Torino, Italy
  • , L. NataleAffiliated withINFM - Dipartimento di Fisica, Politecnico di Torino, 10129 Torino, Italy
  • , G.A. UmmarinoAffiliated withINFM - Dipartimento di Fisica, Politecnico di Torino, 10129 Torino, Italy
  • , V.A. StepanovAffiliated withP.N. Lebedev Physical Institute, Russian Academy of Sciences, 117924 Moscow, Russia
  • , M. FerrettiAffiliated withDipartimento di Chimica e Chimica Industriale, Università di Genova, 16146 Genova, Italy

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Abstract:

We present new Au/La2-xSrxCuO4 (LSCO) point-contact conductance measures as a function of voltage and temperature in samples with 0.08 ? x ? 0.2. Andreev reflection features disappear at about the bulk T c , giving no evidence of gap for T > T c . The fit of the normalized conductance at any T < T c supports a (s + d)-wave symmetry of the gap, whose dominant low-T s component follows the T c ( x ) curve in contrast with recent angle-resolved photoemission spectroscopy and quasiparticle tunneling data. These results prove the separation between pseudogap and phase-coherence superconducting gap in LSCO at x 0.2.

PACS. 74.50.+r Proximity effects; weak links; tunneling phenomena and Josephson effects – 74.25.Dw Superconductivity phase diagrams – 74.72.Dn La-based cuprates