磁性奈米島嶼成長在s-wave超導體上被預測為其中一種可能以人工的方式合成拓樸超導體，在這項研究中，我們延續陳家儒學長之研究[10]，在不同溫度下將鐵磁性元素的Ni成長在Pb(111)基板上，透過掃描穿隧顯微鏡(Scanning Tunneling Spectroscopy)，我們發現鎳會形成鎳鉛合金與單層鎳奈米島。配合第一原理計算，鎳鉛合金會形成雙層結構，以Ni1Pb1所組成六方晶格與四方晶格結構；而單層鎳奈米島則形成蜂巢狀的結構並且具有亮暗兩種邊界，分別對應hcp-site與fcc-site的鎳原子所組成之鬚行邊界((Bearded edges)，而透過dI/dV mapping可以在單層鎳奈米島的邊界外的Pb(111)表面上觀察到由電子所引發的駐波，但只能夠在暗邊觀察到此現象，而這個現象也表示在邊界由fcc-site的鎳原子與底層鉛的鍵結強度比由hcp-site的鎳原子還大。接著我們將溫度降低至0.32K量測掃描穿隧能譜(Scanning Tunneling Spectroscopy)，發現由鄰近效應所引發鎳鉛合金之超導性並非傳統的s-wave 超導體，為具有異相性之超導態，其超導能隙(Superconducting gap)為Δ_NiPb≈0.88meV，比鉛的超導能隙Δ_Pb≈1.22meV小了許多，而同樣由鄰近所引發單層鎳奈米島之超導性，反而比Pb(111)基板要大了一點。

The growth of magnetic nanoislands on superconductors has been predicted to be one of the possibilities for artificially synthesizing topological superconductors. In this work, we are motivated by the previous study[10] to grow Ni on Pb(111) substrate at different temperatures. By using Scanning Tunneling Microscopy and Spectroscopy (STM/STS), we find that Ni-Pb binary alloy and Ni nanoislands with honeycomb structures can be formed on Pb(111). The topography images and first-principle calculations show that Ni-Pb alloy forms a bilayer structures with hexagonal and rectangular lattices. And Ni nanoislands with honeycomb lattice show the bearded edges having both FCC site and HCP site terminations. Scattering of surface electrons by the edges of Ni-island on Pb(111) can be observed from the quasiparticle interference mappings. We also find that only the edges with FCC site termination show scattering events due to stronger and local bonding potential between Ni and Pb. The superconductivity on Ni-Pb alloy induced by the proximity effect represents the anisotropic superconductivity. The superconducting gap (Δ_NiPb≈0.88meV) is smaller than the Pb(111)( Δ_Pb≈1.22meV). On the other hand, the superconductivity on honeycomb Ni nanoislands induced by the proximity effect is slightly enhanced than the Pb (111) substrate.

[1] L. Fu and C. L. Kane, Phys. Rev. Lett. 100, 096407 (2008).
[2] C. W. Beenakker, Rev. Mod. Phys. 69, 731 (1997).
[3] C. Lambert and R. Raimondi, J. Phys. Condens. Matter 10, 901 (1998).
[4] S. Nadj-Perge, I. K. Drozdov, J. Li, H. Chen, S. Jeon, J. Seo, A. H. MacDonald, B. A.Bernevig, and A. Yazdani, Science 346, 602 (2014).
[5] M. Ruby, B. W. Heinrich, Y. Peng, F. von Oppen, and K. J. Franke, Nano Lett.17, 4473 (2017).
[6] A. Palacio-Morales, E. Mascot, S. Cocklin, H. Kim, S. Rachel, D. K. Morr, and R.Wiesendanger, Sci. Adv. 5, eaav6600 (2019).
[7] G. C. Ménard, A. Mesaros, C. Brun, F. Debontridder, D. Roditchev, P. Simon, and T. Cren, Nat. Commun. 10, 1 (2019).
[8] V. Mourik, K. Zuo, S. M. Frolov, S. Plissard, E. P. Bakkers, and L. P. Kouwenhoven, Science 336, 1003 (2012).
[9] S. M. Albrecht, A. P. Higginbotham, M. Madsen, F. Kuemmeth, T. S. Jespersen, J. Nygård, P. Krogstrup, and C. Marcus, Nature 531, 206 (2016).
[10] 陳家儒. (2020). 於單原子層鎳鉛合金與鎳奈米島由鄰近效應所引發之超導態.
[11] L. N. Cooper, Phys. Rev. 104, 1189 (1956).
[12] J. Bardeen, L. N. Cooper, and J. R. Schrieffer, Phys. Rev. 108, 1175 (1957).
[13] Kittel, C. (1976). Introduction to solid state physics.
[14] J. Bardeen and D. Pines, Phys. Rev. 99, 1140 (1955)
[15] H. Frohlich, Proc. Roy. Soc. (London) A215, 291 (1952)
[16] A. P. Mackenzie and Y. Maeno, Rev. Mod. Phys. 75, 657 (2003).
[17] M. Müller, N. Néel, S. Crampin, and J. Kröger, Phys. Rev. Lett. 117, 136803 (2016).
[18] M. Müller, N. Néel, S. Crampin, and J. Kröger, Phys. Rev. B 96, 205426 (2017).
[19] S. Y. Song and J. Seo, Sci. Rep 7, 1 (2017).
[20] E. Boaknin, R.W. Hill, C. Proust, C. Lupien, L. Taillefer, and P.C. Canfield, Phys. Rev. Lett. 87, 237001 (2001).
[21] K. Izawa, K. Kamata, Y. Nakajima, Y. Matsuda, T. Watanabe, M Nohara, H. Takagi, P. Thalmeier, and K. Maki, Phys. Rev. Lett. 89, 137006 (2002).
[22] T. Yokoya, T. Kiss, T. Watanabe, S. Shin, M. Nohara, H. Takagi, and T. Oguchi, Phys. Rev. Lett. 85, 4952 (2000).
[23] K. Izawa, A. Shibata, Y. Matsuda, Y. Kato, H.Takeya, K. Hirata, C.J. van der Beek, and M. Konczykowski, Phys. Rev. Lett. 86, 1327 (2001).
[24] M. Nohara, H. Suzuki, N. Mangkorntong, and H.Takagi, Physica C 341-348, 2177 (2000).
[25] T. Jacobs, B.A. Willemsen, S. Sridhar, R. Nagarajan, L.C. Gupta,Z. Hossain, C. Mazumdar, P.C. Canfield, and B.K. Cho, Phys. Rev. B 52, R7022 (1995).
[26] Martinez-Samper, P., Suderow, H., Vieira, S., Brison, J. P., Luchier, N., Lejay, P., & Canfield, P. C. (2003). Phys Rev B, 67(1),014526.
[27] 伍秀菁、汪若文、林美吟編輯, 真空技術與應用 (國科會精密儀器發展中心, 民90).
[28] Across International. HowScrollPumpsWork. https:
//www.acrossinternational.com/media/HowScrollPumpsWork.gif.
[29] Osaka Vacuum. Turbo Molecular Pumps Exhaust Theory. https://www.osakavacuum.co.jp/en/products/.
[30] Hofmann, P. ion pump https://philiphofmann.net/ultrahighvacuum/
ind_ionpump.html.
[31] Gamma Vacuum. TITANIUM SUBLIMATION PUMPS TSP Cartridges. https://www.gammavacuum.com/index.php/product?id=23.
[32] FOCUS, Instruction Manual UHV Evaporator EFM 2/3(s)/4(s) Triple Evaporator EFM3T(s) IBAD Evaporator EFM 3i (FOCUS GmbH., 2017).
[33] J. Bardeen, Phys. Rev. Lett. 6, 57 (1961).
[34] C. J. Chen, Introduction to Scanning Tunneling Microscopy (Oxford University Press,2008), 2nd edn.
[35] J. Tersoff and D. R. Hamann, Phys. Rev. B 31, 805 (1985).
[36] J. Tersoff and D. R. Hamann, Phys. Rev. Lett. 50, 1998 (1983).
[37] Ukraintsev, V. A. Phys. Rev. B 53, 11176–11185 (1996).
[38] Huda, M. N. Epitaxial growth of lateral graphene / hexagonal boron nitride
heterostructures PhD thesis (2016).
[39] Unisoku.(2018). USM1300S He 3E. Operating Manual.
[40] Grimvall, G., & Sjödin, S. (1974). Correlation of properties of materials to Debye and melting temperatures. Physica Scripta, 10(6), 340.
[41] Liu, R. Y., Huang, A., Huang, C. C., Lee, C. Y., Lin, C. H., Cheng, C. M., ... & Tang, S. J. (2015).Phys Rev B,92(11), 115415.