Point-contact spectroscopy of the electron-doped cuprate superconductor Pr_2-xCe_xCuO₄: The dependence of conductance-voltage spectra on cerium doping, barrier strength, and magnetic field

We present conductance-voltage (G-V) data for point-contact junctions between a normal metal and the electron-doped cuprate superconductor Pr_2-xCe_xCuO₄ (PCCO). We observe a zero-bias conductance peak for the underdoped composition of this cuprate (x=0.13) which is consistent with d-wave pairing symmetry. For optimally doped (x=0.15) and overdoped (x=0.17) PCCO, we find that the G-V characteristics indicate the presence of an order parameter without nodes. We investigate this further by obtaining point-contact spectroscopy data for different barrier strengths and as a function of magnetic field. We observe a gaplike feature at the Fermi energy in the normal state of PCCO (H>˜H_c2) for all dopings.