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Pairing in the cuprate high-temperature superconductors and its origin remain among the most enduring mysteries in condensed matter physics.With cross-sectional scanning tunneling microscopy/spectroscopy we clearly reveal the spatial-dependence or inhomogeneity of the superconducting gap structure of Bi_2Sr_2CaCu_2O_(8+δ)(Bi2212) and YBa_2Cu_3O_(7-x)(YBCO) along their c-axes on a scale shorter than the interlayer spacing.By tunneling into the(100) plane of a Bi2212 single crystal and a YBCO film,we observe both U-shaped tunneling spectra with extended flat zero-conductance bottoms,and V-shaped gap structures,in different regions of each sample.On the YBCO film,tunneling into a(110) surface only reveals a U-shaped gap without any zero-bias peak.Our analysis suggests that the U-shaped gap is likely a nodeless superconducting gap.The V-shaped gap has a very small amplitude,and is likely proximity-induced by regions having the larger U-shaped gap.
Pairing in the cuprate high-temperature superconductors and its origin remain among the most enduring mysteries in condensed matter physics. Cross-sectional scanning tunneling microscopy / spectroscopy we clearly reveal the spatial-dependence or inhomogeneity of the superconducting gap structure of Bi_2Sr_2CaCu_2O_ (8+ δ) (Bi2212) and YBa_2Cu_3O_ (7-x) (YBCO) along their c-axes on a scale shorter than the interlayer spacing. By tunneling into the (100) plane of a Bi2212 single crystal and a YBCO film, we observe both U-shaped tunneling spectra with extended flat zero-conductance bottoms, and V-shaped gap structures, in different regions of each sample. On the YBCO film, tunneling into a (110) surface only reveals a U- shaped gap without any zero- bias peak. Our analysis suggests that the U-shaped gap is likely a nodeless superconducting gap. The V-shaped gap has a very small amplitude, and is likely proximity-induced by regions having the larger U-shaped gap.