在局部有序材料中建立相干的动量空间电子态
Establishing Coherent Momentum-Space Electronic States in Locally Ordered Materials
AI总结：
本研究以Bi$_2$Se$_3$为对象，利用角分辨光电子能谱发现即使在缺乏长程有序的非晶态中，局部有序的真实空间尺度也能产生相干的动量依赖电子态，揭示了电子相干性源于平均最近邻距离的倒数，为在更广泛材料中实现动量依赖量子现象开辟了新途径。
摘要：
在我们对固体的理解中，高度空间相干电子态的形成是控制材料量子行为的基础，它依赖于晶格的离散平移对称性。相反，在缺乏长程有序的情况下，例如非晶态材料，电子态是局域的，且无法发展出电子相干性。这提出了一个根本性问题：长程有序是否是建立相干性和结构化动量依赖电子态的必要条件，以及如何在存在短程有序时对其进行表征。在此，我们研究了Bi$_2$Se$_3$，该材料存在具有长程有序的晶态、具有短中程有序的非晶态以及短程有序减弱的纳米晶态形式。通过使用角分辨光电子能谱以动量分辨方式直接探测电子态，我们揭示了即使在缺乏长程有序的情况下，明确定义的真实空间长度尺度也足以产生色散能带结构。此外，我们首次观察到重复的费米面结构，由复制的环形组成，类似于布里渊区式的重复。这些结果结合我们使用非晶哈密顿量的模拟表明，发生相干的典型动量尺度是平均最近邻距离的倒数，这是底层原子结构局部秩序的直接指纹。这些结果不仅为固体中电子相干性的新理解铺平了道路，也为在比目前研究的缺乏长程晶格平移对称性的更广泛材料类别中实现动量配对和自旋轨道耦合等新型动量依赖量子现象开辟了道路。
英文摘要：
In our understanding of solids, the formation of highly spatially coherent electronic states, fundamental to command the quantum behavior of materials, relies on the existence of discrete translational symmetry of the crystalline lattice. In contrast, in the absence of long-range order, as in the case of non-crystalline materials, the electronic states are localized and electronic coherence does not develop. This brings forward the fundamental question whether long range order is necessary condition to establish coherence and structured momentum-dependent electronic state, and how to characterize it in the presence of short-range order. Here we study Bi$_2$Se$_3$, a material that exists in its crystalline form with long range order, in amorphous form, with short and medium range order, and in its nanocrystalline form, with reduced short range order. By using angle resolved photoemission spectroscopy to directly access the electronic states in a momentum resolved manner, we reveal that, even in the absence of long-range order, a well-defined real-space length scale is sufficient to produce dispersive band structures. Moreover, we observe for the first time a repeated Fermi surface structure of duplicated annuli, reminiscent of Brillouin zone-like repetitions. These results, together with our simulations using amorphous Hamiltonians, reveal that the typical momentum scale where coherence occurs is the inverse average nearest-neighbor distance, the direct fingerprint of the local order of the underlying atomic structure. These results, not only lead the way to a new understanding of electronic coherence in solids, but also open the way to the realization of novel momentum-dependent quantum phenomena such as momentum pairing and spin-orbit coupling, in a much broader class of materials than the currently studied ones, lacking long range crystalline translational symmetry.
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