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Quasiparticle interference and superconducting gap in Ca2−xNaxCuO2Cl2

Nature Physics volume 3, pages 865–871 (2007)Cite this article

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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Figure 1: Schematic illustration of electronic states responsible for the interference effect of Bogoliubov quasiparticles in the superconducting state.
Figure 2: Spectroscopic features of nearly optimally doped Na-CCOC with Tc∼25 K (x∼0.13).
Figure 3: Fourier-transform STS results on Na-CCOC (Tc∼28 K,x∼0.14) demonstrating the QPI in the conductance-ratio map Z(r,E)≡g(r,+E)/g(r,−E).
Figure 4: The obtained FS and the SG dispersion for Na-CCOC (Tc∼28 K,x∼0.14).

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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.

Author information

Authors and Affiliations

  1. Magnetic Materials Laboratory, RIKEN (The Institute of Physical and Chemical Research), Wako 351-0198, Japan

    T. Hanaguri, M. Ono & H. Takagi

  2. CREST, Japan Science and Technology Agency, Kawaguchi 332-0012, Japan

    T. Hanaguri, M. Ono & H. Takagi

  3. Department of Physics, LASSP, Cornell University, Ithaca, New York 14853, USA

    Y. Kohsaka & J. C. Davis

  4. CMPMS Department, Brookhaven National Laboratory, Upton, New York 11973, USA

    J. C. Davis

  5. Département de Physique, Université de Sherbrooke, Sherbrooke, QC J1K 2R1, Canada

    C. Lupien

  6. Institute for Chemical Research, Kyoto University, Uji 601-0011, Japan

    I. Yamada, M. Azuma & M. Takano

  7. Advanced Science Research Center, Japan Atomic Energy Agency, Ibaraki 319-1195, Japan

    K. Ohishi

  8. Department of Advanced Materials, University of Tokyo, Kashiwa 277-8561, Japan

    H. Takagi

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  1. T. Hanaguri
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Contributions

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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Correspondence to T. Hanaguri.

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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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