ITMO University, St. Petersburg, 197101, Russia.
Department of Physics, University of Bath, Bath, BA2 7AY, United Kingdom.
Sci Rep. 2017 May 11;7(1):1780. doi: 10.1038/s41598-017-01646-y.
Matter in nontrivial topological phase possesses unique properties, such as support of unidirectional edge modes on its interface. It is the existence of such modes which is responsible for the wonderful properties of a topological insulator - material which is insulating in the bulk but conducting on its surface, along with many of its recently proposed photonic and polaritonic analogues. We show that exciton-polariton fluid in a nontrivial topological phase in kagome lattice, supports nonlinear excitations in the form of solitons built up from wavepackets of topological edge modes - topological edge solitons. Our theoretical and numerical results indicate the appearance of bright, dark and grey solitons dwelling in the vicinity of the boundary of a lattice strip. In a parabolic region of the dispersion the solitons can be described by envelope functions satisfying the nonlinear Schrödinger equation. Upon collision, multiple topological edge solitons emerge undistorted, which proves them to be true solitons as opposed to solitary waves for which such requirement is waived. Importantly, kagome lattice supports topological edge mode with zero group velocity unlike other types of truncated lattices. This gives a finer control over soliton velocity which can take both positive and negative values depending on the choice of forming it topological edge modes.
非平庸拓扑相中的物质具有独特的性质，例如在其界面上支持单向边缘模式。正是这些模式的存在，使得拓扑绝缘体具有奇妙的性质——这种材料在体相是绝缘的，但在表面是导电的，还有许多最近提出的光子和极化激元类似物。我们表明，在 kagome 晶格中非平庸拓扑相中激子极化激元流体以拓扑边缘模式波包构建的孤子形式支持非线性激发——拓扑边缘孤子。我们的理论和数值结果表明，在晶格带边界附近存在亮、暗和灰色孤子。在色散的抛物区中，孤子可以用满足非线性薛定谔方程的包络函数来描述。在碰撞过程中，多个拓扑边缘孤子会毫发无损地出现，这证明它们是真正的孤子，而不是孤立波，因为孤立波不需要满足这种要求。重要的是，kagome 晶格支持具有零群速度的拓扑边缘模式，这与其他类型的截断晶格不同。这可以更精细地控制孤子速度，根据形成拓扑边缘模式的选择，孤子速度可以取正值或负值。
