紧支撑Wannier函数与严格局部投影
Compactly Supported Wannier Functions and Strictly Local Projectors
摘要：
最大局部化的Wannier函数有助于理解晶体材料的许多性质。在没有拓扑障碍的情况下，它们至少是指数局部的。在某些情况下，例如平带哈密顿，可以构造更局部化的Wannier函数，使得它们是紧支集的，从而在它们对应的位置之外具有零支集。在什么一般条件下可以构造紧支撑的Wannier函数？我们在本文中回答这个问题。具体来说，我们证明了在1d非相互作用紧束缚模型中，投影算子的严格局部性是子空间被紧支撑正交基张成的充分必要条件，与晶格平移对称性无关。对于任何严格的本地投影仪，我们提供了一个程序来获得这样的基础。对于高维系统，我们讨论了紧支撑正交基张成被占子空间的一些附加条件，并证明了在许多情况下相应的投影子是拓扑平凡的.我们还表明，在任意尺寸的投影仪是严格本地的当且仅当对于任何选定的轴，其图像是跨越的混合Wannier功能，紧支持沿该轴。
英文摘要：
Wannier functions that are maximally localized help in understanding many properties of crystalline materials. In the absence of topological obstructions, they are at least exponentially localized. In some cases such as flat-band Hamiltonians, it is possible to construct Wannier functions that are even more localized, so that they are compactly supported thus having zero support outside their corresponding locations. Under what general conditions is it possible to construct compactly supported Wannier functions? We answer this question in this paper. Specifically, we show that in 1d non-interacting tight-binding models, strict locality of the projection operator is a necessary and sufficient condition for a subspace to be spanned by a compactly supported orthogonal basis, independent of lattice translation symmetry. For any strictly local projector, we provide a procedure for obtaining such a basis. For higher dimensional systems, we discuss some additional conditions under which an occupied subspace is spanned by a compactly supported orthogonal basis, and show that the corresponding projectors are topologically trivial in many cases. We also show that a projector in arbitrary dimensions is strictly local if and only if for any chosen axis, its image is spanned by hybrid Wannier functions that are compactly supported along that axis.
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