Chin. Phys. Lett.  2016, Vol. 33 Issue (12): 127402    DOI: 10.1088/0256-307X/33/12/127402
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES |
Possible Nodeless Superconducting Gaps in Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ and YBa$_2$Cu$_3$O$_{7-x}$ Revealed by Cross-Sectional Scanning Tunneling Spectroscopy
Ming-Qiang Ren1,2, Ya-Jun Yan1,2, Tong Zhang1,2**, Dong-Lai Feng1,2**
1State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433
2Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093
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Ming-Qiang Ren, Ya-Jun Yan, Tong Zhang et al  2016 Chin. Phys. Lett. 33 127402
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Abstract

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$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (Bi2212) and YBa$_2$Cu$_3$O$_{7-x}$ (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.
Received: 08 November 2016      Published: 29 December 2016
PACS:  74.20.Rp (Pairing symmetries (other than s-wave))  
  74.25.Jb (Electronic structure (photoemission, etc.))  
  74.55.+v (Tunneling phenomena: single particle tunneling and STM)  
  74.72.-h (Cuprate superconductors)  
Fund:

Supported by the National Natural Science Foundation of China, and the National Key Research and Development Program of China under Grant No 2016YFA0300203.
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https://cpl.iphy.ac.cn/10.1088/0256-307X/33/12/127402       OR      https://cpl.iphy.ac.cn/Y2016/V33/I12/127402
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Ming-Qiang Ren
Ya-Jun Yan
Tong Zhang
Dong-Lai Feng
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