Ideal Weyl semimetal with 3D spin-orbit coupled ultracold quantum gas

理想外尔半金属和三维人工自旋轨道耦合在超冷量子气体中的实现

There is an immense effort in search for various types of Weyl semimetals, of which the most fundamental phase consists of the minimal number of i.e. two Weyl points, but is hard to engineer in solids. Here we demonstrate how such fundamental Weyl semimetal can be realized in a maneuverable optical Raman lattice, with which the three-dimensional(3D) spin-orbit(SO) coupling is synthesised for ultracold atoms. In addition, a new novel Weyl phase with coexisting Weyl nodal points and nodal ring is also predicted here, and is shown to be protected by nontrivial linking numbers. We further propose feasible techniques to precisely resolve 3D Weyl band topology through 2D equilibrium and dynamical measurements. This work leads to the first realization of the most fundamental Weyl semimetal band and the 3D SO coupling for ultracold quantum gases, which are respectively the significant issues in the condensed matter and ultracold atom physics.

寻找各类外尔半金属吸引了极广泛的研究.尽管取得很多进展,但是最基本的理想外尔半金属相,即只有最少(两个)外尔点数的外尔半金属却存在实现困难.只有两个外尔点的外尔半金属在理论和实验研究上均有特殊意义.另外,基于超冷原子进行拓扑量子模拟是重要方向.然而基于超冷原子实现外尔半金属面临挑战:长期以来超冷原子一直未能实现三维人工自旋轨道耦合,这是实现外尔半金属的基本前提.本文提出几何构型可控的拉曼光晶格方案,克服过去所有困难,不仅成功实现三维人工自旋轨道耦合和理想外尔半金属,并预言外尔点和节线圈共存的新外尔相.作者证明这种共存相由连环拓扑数刻画.进一步,作者提出称为虚拟断层扫描的技术,使得仅由二维测量可重建三维拓扑能带结构.该工作导致理想外尔半金属和三维人工自旋轨道耦合基于超冷原子的首次实现,将推动该领域多方发展.