Andreev reflections and tunneling spectroscopy on underdoped
Université Libre de Bruxelles, Service de Physique des Solides
CP233, Blvd du Triomphe, B-1050 Brussels, Belgium
Accepted: 31 March 2000
Andreev-reflection and tunneling studies have been carried out on a single crystal of underdoped (NCCO) by using Ag, Pt-Ir and Nb tips to clarify the symmetry of its order parameter. Surprisingly, we observed in the NCCO, on the one hand, the Josephson current (with Nb tip) which indicates the presence of s-wave order parameter, on the other hand, a zero-bias conductance peak (with Ag tip) which is a manifestation of d-wave order parameter. In addition, we find the presence of two distinct energy scales in the underdoped NCCO: the smallest energy scale is associated with the Andreev gap and c-axis tunneling gap, and the second scale corresponds to the maximum in-plane tunneling gap. It seems that the phenomenon of superconductivity in electron- and hole-doped cuprates can be understood within a common scheme.
PACS: 74.50.+r – Proximity effects, weak links, tunneling phenomena, and Josephson effects / 74.72.Jt – Other cuprates / 74.25.Dw – Superconductivity phase diagrams
© EDP Sciences, 2000