Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada.
Phys Rev Lett. 2023 Jan 27;130(4):043801. doi: 10.1103/PhysRevLett.130.043801.
Systems with strong light-matter interaction open up new avenues for studying topological phases of matter. Examples include exciton polaritons, mixed light-matter quasiparticles, where the topology of the polaritonic band structure arises from the collective coupling between matter wave and optical fields strongly confined in periodic dielectric structures. Distinct from light-matter interaction in a uniform environment, the spatially varying nature of the optical fields leads to a fundamental modification of the well-known optical selection rules, which were derived under the plane wave approximation. Here we identify polaritonic Chern insulators by coupling valley excitons in transition metal dichalcogenides to photonic Bloch modes in a dielectric photonic crystal slab. We show that polaritonic Dirac points, which are markers for topological phase transition points, can be constructed from the collective coupling between valley excitons and photonic Dirac cones in the presence of both time-reversal and inversion symmetries. Lifting exciton valley degeneracy by breaking time-reversal symmetry leads to gapped polaritonic bands with nonzero Chern numbers. Through numerical simulations, we predict polaritonic chiral edge states residing inside the topological gaps. Our Letter paves the way for the further study of strong exciton-photon interaction in nanophotonic structures and for exploring polaritonic topological phases and their practical applications in polaritonic devices.
具有强光物质相互作用的系统为研究物质的拓扑相开辟了新途径。例如激子极化激元，混合光物质准粒子，其中极化激元能带结构的拓扑结构源于物质波和光学场之间的集体耦合，光学场在周期性介电结构中被强烈限制。与均匀环境中的光物质相互作用不同，光学场的空间变化性质导致了众所周知的光学选择规则的基本修正，这些规则是在平面波近似下推导出来的。在这里，我们通过将过渡金属二卤化物中的谷激子耦合到介电光子晶体平板中的光子布洛赫模式，来识别极化激子 Chern 绝缘体。我们表明，在时间反演和反转对称性的存在下，通过谷激子和光子狄拉克锥之间的集体耦合，可以构建出拓扑相变点的极化激子 Dirac 点。通过打破时间反演对称性来消除激子谷简并性，会导致具有非零 Chern 数的带隙极化激子能带。通过数值模拟，我们预测了位于拓扑间隙内的极化激子手性边缘态。我们的信件为进一步研究纳米光子结构中的强激子光子相互作用以及探索极化激子拓扑相及其在极化激子器件中的实际应用铺平了道路。
