Tunneling characteristics of La2-xSrxCuO4-y metal contacts

This paper reports that in order to investigate the electronic state locating in the Hubbard gap of the oxide superconductor, the electron tunneling spectra ranging of ∼±1.2 eV were observed for the La2-xSrxCuO4-y (0.04 ≤ x ≤ 0.4) system. Upon the polished surface of sintered or single crystal specimens, metal gold film of submicron thickness was vacuum deposited with a large contact area of 10-3 cm2. Observed tunneling conductance spectra showed some systematic characteristics; for x = 0.04 the V-shaped spectrum with vanishing conductance at zero-bias point, for x = 0.4 high level conductance over the bias range, and for x = 0.19 the intermediate characters