Evidence for pseudogap and phase-coherence gap separation by Andreev reflection experiments in Au/ La2 - xSrxCuO4 point-contact junctions

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 Tc, giving no evidence of gap for T > Tc. The fit of the normalized conductance at any T < Tc supports a (s + d)-wave symmetry of the gap, whose dominant low-Ts component follows the Tc(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.