Investigation of Nd-Ce-Cu-O planar tunnel junctions and bicrystal grain boundary junctions

Abstract

We have fabricated planar c-axis Pb/NCCO junctions and in-plane NCCO bicrystal grain boundary junctions. The Pb/NCCO junctions exhibit single-step elastic tunneling and sustain hysteretic Josephson supercurrents, evidence that NCCO has an s-wave component to its superconducting order parameter. Tunneling spectroscopy on high-resistance Pb/NCCO junctions reveals a semi-gap of 3-4 meV in the density of states of NCCO and evidence for phonon coupling to NCCO quasiparticles. The grain boundary junctions were made by laser ablating thin NCCO films onto yttrium-stabilized-zirconia bicrystal substrates and sustain supercurrents that modulate in applied magnetic field and show resistively-shunted-junction I-V characteristics.