光诱导蜂窝型光子晶格中与赝自旋相关涡旋现象的研究

Graphene is a two-dimensional material which has attracted great attention in condensed matter physics due to its unique band gap structure with Dirac cones. Recently, various artificial graphene-like periodic structures have been proposed to simulate fundamental physical phenomena in graphene. In this project, we propose a method to fabricate graphene-like photonic periodic structures in a bulk nonlinear crystal by the optical induction method. Such honeycomb photonic lattices provide a useful and controllable platform to explore fundamental graphene physics, some of which are even inaccessible in real graphene. In this proposal we plan to use the optically induced graphene-like periodic structure to study the pseudospin-mediated vortex generation. By selectively excitation of the two sublattices, various pseudospin-mediated vortex generation phenomena including the fractional charged vortex and the integer charged vortex will be realized. We want to reveal the underlying physics of interaction between pseudospin and angular momentum. We will also investigate the pseudospin-mediated phenomena in deformed honeycomb photonic lattices, and unveil the relationship between pseudospin angular momentum and Dirac cone band structures. Moreover, we want to uncover the underlying physics between pseudospin ,angular momentum and Dirac cone and realize controllable generation of the pseudospin-mediated angular momentum. Our research not only provides a new physical mechanism of generating optical vortex beam with orbital angular momentum, but also has direct impact on the study of pseudospin-mediated vortex phenomena in other periodic structures with Dirac cone.

石墨烯是一种具有狄拉克锥能带结构的二维材料，在凝聚态物理中引起了人们极大的关注。最近人们发现可以构建参数可调的人工石墨烯结构来类比研究石墨烯中的多种基本物理现象。本项目提出利用光学诱导的方法在非线性晶体中制备出类石墨烯型的光学周期结构---蜂窝型光子晶格，然后利用该光学平台来类比研究在石墨烯中很难实验实现的物理现象---赝自旋。通过选择激发蜂窝型光子晶格的不同子晶格来实现与赝自旋相关的多种涡旋现象包括分数光涡旋与整数光涡旋，揭示赝自旋与角动量相互作用与转化的物理机制；通过研究变形蜂窝型光子晶格中与赝自旋相关的涡旋现象，阐明赝自旋涡旋与狄拉克锥能带结构之间的关系；最终揭示赝自旋、角动量、狄拉克锥能带结构之间的内在物理规律，实现赝自旋角动量的可控产生。我们的研究不仅提供了一种产生具有轨道角动量涡旋光的新方法与新物理机制，而且对其它人工石墨烯系统甚至碳石墨烯中赝自旋现象的研究也具有借鉴作用。

石墨烯是一种具有狄拉克锥能带结构的二维材料，在凝聚态物理中引起了人们极大的关注。最近人们发现可以构建参数可调的人工石墨烯结构来类比研究石墨烯中难以实现的新颖物理现象。在项目执行期，我们以光诱导制备的石墨烯型光子晶格为平台实现了多种与赝自旋自由度相关的物理现象，包括能谷涡旋产生与涡旋简并破除、赝自旋与轨道角动量的相互作用导致的涡旋拓扑荷转换，梯度场下的布洛赫震荡与赝自旋破缺等，揭示了动量空间能带拓扑奇点与实空间拓扑奇点的普适关联。此外，我们也将相关的研究拓展到了赝自旋为1的狄拉克光子晶格中，并实现了多种实空间拓扑特性保护的非传统平带模式。这些结果对其他类狄拉克体系的相关研究也具有借鉴意义。项目共发表SCI论文14篇， 其中包括Nat.Commun. 1篇，Phys. Rev. Lett. 4篇，毕业博士研究2人，硕士研究生4人， 项目负责人获得了2019年优秀青年基金项目资助。