Possible Nodeless Superconducting Gaps in Bi2Sr2CaCu2O8＋δ and YBa2Cu3O7-x Revealed by Cross-Sectional Scanning Tunneling Spectroscopy

• Published in: 中国物理快报：英文版 Vol. 33; no. 12; pp. 124 - 128
• Main Author: 任明强 闫亚军 张童 封东来
• Format: Journal Article
• Language: English
• Published: 01.12.2016
• Subjects: Bi2212单晶; YBa2Cu3O7-x; YBCO薄膜; 扫描隧道显微术; 扫描隧道谱; 横断面; 氧化物高温超导体; 超导能隙
• ISSN: 0256-307X; 1741-3540
• DOI: 10.1088/0256-307X/33/12/127402

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 Bi2Sr2CaCu2O8＋δ （Bi2212） and YBa2Cu3O7-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 fiat 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.