It has been well established that the presence of quantum-well states in metal thin films plays an essential role in determining the thickness dependence of many physical properties. Oscillatory features in these properties are often observed and attributed to the energy variations of these quantum-well states near the Fermi level. Modern film growth capability has made it possible to create composite metal thin films in which one metal thin film is stacked on top of a dissimilar one with precise control of individual thickness. How the original quantum-well states evolve in the composite film becomes a critical issue in understanding the electronic structure of these new complex thin-film systems. In this paper we present first-principles calculations and measurements by angle-resolved photoemission spectroscopy for electronic states in a bimetallic film composed of ten layers of Pb and nine layers of Ag in the [111] direction on a Si substrate. It is found that the original quantum-well states in individual Pb and Ag films evolve into a new set of states in the bimetallic film by extending into the additional space, instead of directly coupling with each other as one would have expected. The new set of quantum-well states therefore has modified effective masses and energy values compared with the parent ones. Even though the Pb/Ag interface is incommensurate, the coherently coupled electronic states across the whole bimetallic film are verified by supercell configurations with different rotational arrangements in the calculation. The excellent agreement between theory and experiment in the energy dispersion of the quantum-well states in this bimetallic film confirms the physical picture proposed in this work, which could form the basis for exploring the electronic structure in multiple stacked thin films with more complicated designs.

中文翻译：

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双金属Pb / Ag薄膜中的相干耦合量子阱态

众所周知，金属薄膜中量子阱态的存在对于确定许多物理性质的厚度依赖性起着至关重要的作用。这些性质的振荡特征经常被观察到，并且归因于这些费米能级附近的量子阱态的能量变化。现代的薄膜生长能力使得制造复合金属薄膜成为可能，在该复合金属薄膜中，一种金属薄膜堆叠在另一种薄膜之上，并且可以精确地控制各个厚度。在理解这些新的复杂薄膜系统的电子结构中，原始量子阱态如何在复合膜中演化成为一个关键问题。在本文中，我们介绍了通过角分辨光发射光谱法对Si衬底上由十层Pb和九层Ag沿[111]方向组成的双金属膜中的电子态进行第一性原理的计算和测量。已经发现，单个Pb和Ag膜中的原始量子阱状态通过扩展到附加空间中而演变为双金属膜中的一组新状态，而不是像人们期望的那样彼此直接耦合。因此，与母态相比，新的量子阱态集修改了有效质量和能量值。即使Pb / Ag界面不相称，在整个双金属薄膜中相干耦合的电子态仍通过计算中具有不同旋转排列的超级电池构型得以验证。