Local tunneling measurements of the high-Tc superconductor La2−xSrxCuO4−y

Abstract

We have measured the current-voltage (I-V) characteristics for tunneling into the superconducting layered copper oxide ${\mathrm{La}}_{2\mathrm{-}\mathrm{x}}$ ${\mathrm{Sr}}_{\mathrm{x}}$ ${\mathrm{CuO}}_{4\mathrm{-}\mathrm{y}}$ using a low-temperature scanning-tunneling microscope. The I-V curves were highly nonlinear, even at low voltages, with evidence for superconducting energy gaps Δ of several meV. Substantial variation of Δ was observed from measurement to measurement, with the largest being Δ∼7 meV, corresponding to 2Δ/$k_B$ $T_c$∼4.5. .AE