Abstract
High-transition-temperature (high-Tc) superconductivity is ubiquitous in the cuprates containing CuO2 planes, but each cuprate has its own character. The study of the material dependence of the d-wave superconducting gap (SG) should provide important insights into the mechanism of high-Tc superconductivity. However, because of the ‘pseudogap’ phenomenon, it is often unclear whether the energy gaps observed by spectroscopic techniques really represent the SG. Here, we use scanning tunnelling spectroscopy to image nearly optimally doped Ca2−xNaxCuO2Cl2(Na-CCOC) with Tc=25–28 K. It enables us to observe the quasiparticle interference effect in this material, through which we obtain unambiguous information on the SG. Our analysis of quasiparticle interference in Na-CCOC reveals that the SG dispersion near the gap node is almost identical to that of Bi2Sr2CaCu2Oy (Bi2212) at the same doping level, despite the Tc of Bi2212 being three times higher than that of Na-CCOC. We also find that the SG in Na-CCOC is confined in narrower energy and momentum ranges than Bi2212, which explains—at least in part—the remarkable material dependence of Tc.
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Acknowledgements
The authors thank A.V. Balatsky, C.-M. Ho, D.-H. Lee, K. Machida, A. Mackenzie, K. McElroy, T. Tohyama, J. Zaanen and F.-C. Zhang for discussions. They also thank J. Matsuno and P. Sharma for critical readings. T.H., M.T. and H.T. are supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan. J.C.D. and Y.K. acknowledge support from Brookhaven National Laboratory under contract No DE-AC02-98CH1886 with the US Department of Energy, from the US Department of Energy Award No DE-FG02-06ER46306 and from the US Office of Naval Research.
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T.H. was responsible for all aspects of this project except sample growth. Y.K., J.C.D. and C.L. contributed the project planning and data analysis. I.Y., M.A., M.T. and K.O. grew samples and M.O. contributed the STM measurements. H.T. contributed the project planning and managed the whole project.
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Hanaguri, T., Kohsaka, Y., Davis, J. et al. Quasiparticle interference and superconducting gap in Ca2−xNaxCuO2Cl2. Nature Phys 3, 865–871 (2007). https://doi.org/10.1038/nphys753
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DOI: https://doi.org/10.1038/nphys753
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