Pb € ¾U c lT c l; c ] k ùV R Ëc Ü R Au-Pb ¶  ¥ Œ £ ?; c 6 ” X ¢ — ¤ ' [, f Ç S Ë Ø° Ä Z Ë Ñ] K ¡ Ž ì ŏ Œ

Scanning Tunneling Spectroscopy Study of Au-Pb Alloys Formed on Pb Mesa Islands

Jungdae Kim

Department of Physics, University of Ulsan, Ulsan 44610, Korea (Received 25 April 2015 : revised 26 June 2015 : accepted 5 August 2015)

Quantum-well states (QWSs) and superconducting properties were studied for Au-Pb alloys (type A, type B, and a Moir´e pattern island) formed on top of Pb mesa islands via low-temperature scanning tunneling microscopy. Type A islands behaved just like 1 ML (monolayer) Pb based on the measured QWSs and superconducting gap. On the contrary, type B islands showed significantly suppressed QWSs while having a persistent superconducting gap. For Moir´e pattern islands, the QWSs and the superconducting gap were obtained at the peak and the valley of the Moir´e pattern.

As with type B islands, the peak of the Moir´e pattern presented severely damped QWSs, but still exhibited a clear superconducting gap. The QWSs originated from the strong vertical quantum confinement of the Pb mesa island. Our result indicates that vertical confinement has no influence on superconductivity because superconductivity can be maintained through lateral coherence with nearby Pb.

PACS numbers: 68.35.bd, 68.37.Ef, 68.65.Fg

Keywords: STM, STS, Au-Pb alloy, Superconducting gap, Quantum-well state

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PACS numbers: 68.35.bd, 68.37.Ef, 68.65.Fg

Keywords:ÅÒ'V,aA‰&³p, Åâ Ò'V,aAìrFgÆ, Au-Pb ½†< ËF+K,œí„•¸ :£§,œ€ªĺÓüt©œI

∗E-mail: [email protected]

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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REFERENCES

[1] Z. Y. Zhang, Q. Niu and C. K. Shih, Phys. Rev.

Lett. 80, 5381 (1998).

[2] M. H. Upton, C. M. Wei, M. Y. Chou, T. Miller and T. C. Chiang, Phys. Rev. Lett. 93, 026802 (2004).

[3] A. R. Smith, K. J. Chao, Q. Niu and C. K. Shih, Science 273, 226 (1996).

[4] H. Oughaddou, C. Leandri, B. Aufray, C. Gi- rardeaux and J. Bemardini et al., Appl. Surf. Sci.

212, 291 (2003).

[5] S. H. Chang, W. B. Su, W. B. Jian, C. S. Chang and L. J. Chen et al., Phys. Rev. B 66, 245401 (2002).

[6] D. A. Luh, T. Miller, J. J. Paggel, M. Y. Chou and T. C. Chiang, Science 292, 1131 (2001).

[7] P. Czoschke, H. Hong, L. Basile and T. C. Chiang, Phys. Rev. B 72, 075402 (2005).

[8] S. M. Lu, M. C. Yang, W. B. Su, C. L. Jiang and T. Hsu et al., Phys. Rev. B 75, 113402 (2007).

[9] J. Kim, S. Qin, W. Yao, Q. Niu and M. Y. Chou et al., Proc. Natl. Acad. Sci. USA 107, 12761 (2010).

[10] X. C. Ma, P. Jiang, Y. Qi, J. F. Jia and Y. Yang et al., Proc. Natl. Acad. Sci. USA 104, 9204 (2007).

[11] S. Y. Qin, J. Kim, Q. Niu and C. K. Shih, Science 324, 1314 (2009).

[12] M. M. Ozer, Y. Jia, Z. Y. Zhang, J. R. Thompson and H. H. Weitering, Science 316, 1594 (2007).

[13] Y. Guo, Y. F. Zhang, X. Y. Bao, T. Z. Han and Z.

Tang et al., Science 306, 1915 (2004).

[14] D. Eom, S. Qin, M. Y. Chou and C. K. Shih, Phys.

Rev. Lett. 96, 027005 (2006).

[15] C. M. Wei and M. Y. Chou, Phys. Rev. B 66, 233408 (2002).

[16] P. S. Kirchmann, M. Wolf, J. H. Dil, K. Horn and U. Bovensiepen, Phys. Rev. B 76, 075406 (2007).

[17] Y. Jia, B. Wu, H. H. Weitering and Z. Y. Zhang, Phys. Rev. B 74, 035433 (2006).

[18] T. Schmidt and E. Bauer, Phys. Rev. B 62, 15815 (2000).

[19] J. Kim, S. Qin, Y. Zhang, W. Zhu and C.-K. Shih, Surf. Sci. 632, 174 (2015).

[20] V. Yeh, L. Berbil-Bautista, C. Z. Wang, K. M. Ho and M. C. Tringides, Phys. Rev. Lett. 85, 5158 (2000).