當磁性原子被放置在s-wave超導體附近時，它會對準粒子 (quasiparticle) 展現出交互散射勢 (scattering potential)，接著Yu-Shiba-Rusinov bound state (亦簡稱為YSR or Shiba state) 會出現在超導能隙中，此束縛態提供了我們關於磁性原子與超導體的耦合力強度的資訊，除了單一磁性元素，因為發現了馬約拉納模式，對於量子計算這是一個有前途的平台，超導體上的一維與二維磁性奈米結構也引起了人們的興趣，因此研究磁性元素和超導體之間的交互作用已變得更加重要。
在本研究中，我們透過掃描穿隧顯微鏡進行0.32 K下的低溫量測，並延續先前陳家儒學長[1]與葉大有學長[2]之研究，成功在低溫下成長出具有2×2晶格週期的單原子Ni Kagome晶格，並配合第一原理計算的結果，我們發現在Ni Kagome結構底部存在Ni的次表面 (subsurface) 原子，使得此奈米島具有兩種不同的邊緣高度，並且在邊緣觀察到不對稱的駐波條紋，此外在能帶結構圖中，可以清楚的看見其flat band與Dirac cone的特性。藉由掃描穿隧能譜探索此Ni Kagome結構，我們發現它被Pb(111)基板的鄰近效應誘導出超導特性，有趣的是由於hole doping效應的原因，Ni Kagome結構的超導能隙 (∆_(〖Ni〗_Kagome )≈ 1.29 meV) 相比其超導性來源的Pb(111)基板 (∆_(Pb(111))≈ 1.25 meV) 有些微的增強。
接著我們研究Co與Fe原子在Ni Kagome Lattice上的特性。在Co/Ni/Pb(111)系統中，單一Co原子在Ni Kagome結構與乾淨的Pb(111)基板上，沒有展現出Shiba state的訊號，也代表著在此系統中Co原子沒有磁矩；在Fe/Ni/Pb(111)系統中，我們可以明顯的觀察到單一Fe原子在Ni Kagome結構上的Shiba state，而Fe吸附原子具有兩種主要的形式，藉由高度的差異我們稱為「亮點」與「暗點」，有趣的是它們具有不同的耦合狀態，分別為「亮點」屬於弱耦合狀態，束縛態能量為 0.72 meV ；「暗點」則屬於強耦合狀態，束縛態能量為 -0.36 meV 。最後透過dI/dU mapping來探索Fe原子在Ni Kagome結構上Shiba state的自旋軌域結構。

When magnetic impurities are placed in the proximity to a s-wave superconductor, the Yu-Shiba-Rusinov (YSR or Shiba, in short) bound states can appear inside the superconducting gap because magnetic impurities will exhibit a scattering potential to quasiparticle. The bound state energy can provide us information about the coupling strength between magnetic impurities and superconductors. Beside single magnetic impurities, 1D and 2D magnetic nanostructure on superconductor have attracted interesting because of the finding of Majorana mode, which is a promising platform for quantum computing. Therefore, studding the interaction between magnetic impurities and superconductors has become more important.
In this work, we used scanning tunneling microscopy for low-temperature measurements at 0.32K. We are motivated by the previous study[1,2] and successfully grew a monatomic Ni Kagome structure with a (2x2) lattice periodicity at low temperature. Combine with the results of the first-principle calculations, we found that there are Ni subsurface atoms at the bottom of the Ni Kagome structure, which makes the nanoislands with two kinds of edge height and results in asymmetric scattering events at the edge. In addition, the feature of the flat band and Dirac cone can be clearly seen in the band structure. To investigate the Ni Kagome structure by Scanning Tunneling Spectroscopy, we found that its superconductivity is induced by the proximity effect of the Pb(111) substrate. Interestingly, due to the hole doping effect[3], the superconducting gap of Ni Kagome structure (∆_(〖Ni〗_Kagome )≈ 1.29 meV) slightly enhanced comparing to Pb(111) substrate (∆_(Pb(111))≈ 1.25 meV) .
Then, we study the properties of the magnetic impurities Co or Fe atoms on Ni Kagome Lattice. In the Co/Ni/Pb(111) system, a single Co atom on the Ni Kagome structure and the bare Pb(111) substrate do not exhibit Shiba state signal, which implies that the Co atom have no magnetic moment in this system; in the Fe/Ni/Pb(111) system, we can clearly observe the Shiba state of a single Fe atom on Ni Kagome Lattice. The Fe adatoms have two major type, which are called “bright dot” and “dark dot” by the height difference. Interestingly, they are in different coupling regime: “bright dot” is in weak coupling regime with bound energy of 0.72 meV and “dark dot” is in strong regime with bound energy of -0.36 meV. Finally, We investigate the spin orbital structure of Shiba state of the Fe adatoms on Ni Kagome Lattice by dI/dU mapping.

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