近日，西班牙马德里自治大学的 Hermann Suderow课题组与日本东北大学的Dai Aoki以及法国格勒诺布尔阿尔卑斯大学的Jacques Flouquet等人合作，研究了重费米子超导体表面的量子阱态。相关成果已于2023年3月22日在国际权威学术期刊《自然》上发表。
该课题组使用米开文扫描隧道显微镜(STM)，研究了重费米子超导体URu2Si2的U端表面上的原子平坦台阶，该超导体在17.5K以下表现出神秘的隐藏序（HO）态。研究人员观察到由5f电子构成的2DHFs，其有效质量是自由电子质量的17倍。2DHFs以meV分数形成了量子态之间的分离，其能级宽度由关联体态的相互作用决定。研究还发现，表面台阶之间的边缘态沿着两个平面方向之一出现，表明表面上的电子对称性破缺。该研究提出了一条在强关联量子材料中实现量子阱态的新途径，并探索了这些态与电子环境之间的联系。
据介绍，表面上的二维电子态通常在简单的宽带金属，如Cu或Ag中观察到。在纳米尺度下通过封闭的几何结构（如表面台阶）限制，会导致表面带的量子化能级形成，与体电子带的连续能量依赖形成鲜明对比。尽管二维重费米子(2DHFs)中的量子阱态能级分离通常只有几百毫电子伏，但由于它们微小的能量分离，观察到这些态非常困难。
附：英文原文
Title: Quantum-well states at the surface of a heavy-fermion superconductor
Author: Herrera, Edwin, Guillamn, Isabel, Barrena, Vctor, Herrera, William J., Galvis, Jose Augusto, Yeyati, Alfredo Levy, Rusz, Jn, Oppeneer, Peter M., Knebel, Georg, Brison, Jean Pascal, Flouquet, Jacques, Aoki, Dai, Suderow, Hermann
Issue&Volume: 2023-03-22
Abstract: Two-dimensional electronic states at surfaces are often observed in simple wide-band metals such as Cu or Ag (refs.1,2,3,4). Confinement by closed geometries at the nanometre scale, such as surface terraces, leads to quantized energy levels formed from the surface band, in stark contrast to the continuous energy dependence of bulk electron bands2,5,6,7,8,9,10. Their energy-level separation is typically hundreds of meV (refs.3,6,11). In a distinct class of materials, strong electronic correlations lead to so-called heavy fermions with a strongly reduced bandwidth and exotic bulk ground states12,13. Quantum-well states in two-dimensional heavy fermions (2DHFs) remain, however, notoriously difficult to observe because of their tiny energy separation. Here we use millikelvin scanning tunnelling microscopy (STM) to study atomically flat terraces on U-terminated surfaces of the heavy-fermion superconductor URu2Si2, which exhibits a mysterious hidden-order (HO) state below 17.5K (ref.14). We observe 2DHFs made of 5f electrons with an effective mass 17 times the free electron mass. The 2DHFs form quantized states separated by a fraction of a meV and their level width is set by the interaction with correlated bulk states. Edge states on steps between terraces appear along one of the two in-plane directions, suggesting electronic symmetry breaking at the surface. Our results propose a new route to realize quantum-well states in strongly correlated quantum materials and to explore how these connect to the electronic environment.
DOI: 10.1038/s41586-023-05830-1
Source: https://www.nature.com/articles/s41586-023-05830-1
来源：科学网 小柯机器人