近日，美国麻省理工学院的Joseph G.Checkelsky及其研究小组取得一项新进展。经过不懈努力，他们发现烧绿石金属CaNi₂中的三维平带。相关研究成果已于2023年11月8日在国际权威学术期刊《自然》上发表。

该研究团队对C15 Laves相金属CaNi₂进行了深入研究，该金属包含一个模型网络水平预测的镍烧绿石型晶格，用以容纳由电子跳跃的三维相消干涉引起的双简并拓扑平带。通过利用角度分辨光发射光谱技术，研究人员观察到了在整个三维布里渊区中存在一个色散为零的带，将其认定为焦绿石平带，并发现了另外两个额外的平带。进一步的研究表明，这些平带是由Ni d-电子的多轨道干涉所引起的。此外，研究人员还证明了平带流形可以通过化学调谐达到费米能级，与增强的电子关联性和超导性的出现相一致。这一发现将固有带平坦度的概念从二维扩展到了三维，为预测从可调谐拓扑到分数相的高维平带系统中的相关行为提供了潜在途径。

据悉，电子平带材料具有独特的量子态，其特征为淬灭动能。这些平带通常有助于增强电子关联效应，以及物质的涌现量子相。经过理论模型中的长期研究后，这些系统在范德华异质结构和准二维晶体材料中得到了实验验证，再次激发了人们的兴趣。目前，一个备受关注的实验问题是，能否在三维网络中实现这种平带，以期开发出新的材料平台和现象。

附：英文原文

Title: Three-dimensional flat bands in pyrochlore metal CaNi₂

Author: Wakefield, Joshua P., Kang, Mingu, Neves, Paul M., Oh, Dongjin, Fang, Shiang, McTigue, Ryan, Frank Zhao, S. Y., Lamichhane, Tej N., Chen, Alan, Lee, Seongyong, Park, Sudong, Park, Jae-Hoon, Jozwiak, Chris, Bostwick, Aaron, Rotenberg, Eli, Rajapitamahuni, Anil, Vescovo, Elio, McChesney, Jessica L., Graf, David, Palmstrom, Johanna C., Suzuki, Takehito, Li, Mingda, Comin, Riccardo, Checkelsky, Joseph G.

Issue&Volume: 2023-11-08

Abstract: Electronic flat-band materials host quantum states characterized by a quenched kinetic energy. These flat bands are often conducive to enhanced electron correlation effects and emergent quantum phases of matter. Long studied in theoretical models, these systems have received renewed interest after their experimental realization in van der Waals heterostructures and quasi-two-dimensional (2D) crystalline materials. An outstanding experimental question is if such flat bands can be realized in three-dimensional (3D) networks, potentially enabling new materials platforms and phenomena. Here we investigate the C15 Laves phase metal CaNi₂, which contains a nickel pyrochlore lattice predicted at a model network level to host a doubly-degenerate, topological flat band arising from 3D destructive interference of electronic hopping. Using angle-resolved photoemission spectroscopy, we observe a band with vanishing dispersion across the full 3D Brillouin zone that we identify with the pyrochlore flat band as well as two additional flat bands that we show arise from multi-orbital interference of Ni d-electrons. Furthermore, we demonstrate chemical tuning of the flat-band manifold to the Fermi level that coincides with enhanced electronic correlations and the appearance of superconductivity. Extending the notion of intrinsic band flatness from 2D to 3D, this provides a potential pathway to correlated behaviour predicted for higher-dimensional flat-band systems ranging from tunable topological to fractionalized phases.

DOI: 10.1038/s41586-023-06640-1

Source: https://www.nature.com/articles/s41586-023-06640-1