Huang Hao, Zheng Lixuan, Lin Zhiyong, Guo Xu, Wang Sheng, Zhang Shuai, Zhang Chi, Sun Zhe, Wang Zhengfei, Weng Hongming, Li Lin, Wu Tao, Chen Xianhui, Zeng Changgan
CAS Key Laboratory of Strongly Coupled Quantum Matter Physics, Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China.
Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026, China.
Phys Rev Lett. 2022 Mar 4;128(9):096601. doi: 10.1103/PhysRevLett.128.096601.
For solids, the dispersionless flat band has long been recognized as an ideal platform for achieving intriguing quantum phases. However, experimental progress in revealing flat-band physics has so far been achieved mainly in artificially engineered systems represented as magic-angle twisted bilayer graphene. Here, we demonstrate the emergence of flat-band-dominated anomalous transport and magnetic behaviors in CoSn, a paramagnetic kagome-lattice compound. By combination of angle-resolved photoemission spectroscopy measurements and first-principles calculations, we reveal the existence of a kagome-lattice-derived flat band right around the Fermi level. Strikingly, the resistivity within the kagome lattice plane is more than one order of magnitude larger than the interplane one, in sharp contrast with conventional (quasi-) two-dimensional layered materials. Moreover, the magnetic susceptibility under the out-of-plane magnetic field is found to be much smaller as compared with the in-plane case, which is revealed to be arising from the introduction of a unique orbital diamagnetism. Systematic analyses reveal that these anomalous and giant anisotropies can be reasonably attributed to the unique properties of flat-band electrons, including large effective mass and self-localization of wave functions. Our results broaden the already fascinating flat-band physics, and demonstrate the feasibility of exploring them in natural solid-state materials in addition to artificial ones.
对于固体而言，无色散平带长期以来一直被认为是实现有趣量子相的理想平台。然而，迄今为止，揭示平带物理的实验进展主要是在以魔角扭曲双层石墨烯为代表的人工工程系统中取得的。在这里，我们展示了在顺磁 Kagome 晶格化合物 CoSn 中出现的平带主导的反常输运和磁行为。通过结合角分辨光电子能谱测量和第一性原理计算，我们揭示了在费米能级附近存在一个由 Kagome 晶格衍生的平带。引人注目的是，Kagome 晶格平面内的电阻率比平面间的电阻率大一个多数量级，这与传统的（准）二维层状材料形成鲜明对比。此外，发现平面外磁场下的磁化率与平面内情况相比要小得多，这被揭示是由于引入了独特的轨道抗磁性。系统分析表明，这些反常和巨大的各向异性可以合理地归因于平带电子的独特性质，包括大有效质量和波函数的自局域化。我们的结果拓宽了已经引人入胜的平带物理，并证明了除了人工材料之外，在天然固态材料中探索它们的可行性。
