A study from MRSEC seed led by Ritesh Agarwal published in Science, reports a new type of quasiparticle, helical topological exciton-polaritons in a system of monolayer of tungsten sulfide strongly coupled to a photonic crystal. Exciton-polaritons, which are half-light half-matter quasiparticles inherit useful properties of their constituents but typically suffer from scattering losses. By creating a new type of topological insulator for polaritons, the Agarwal group demonstrated propagation of polaritons around sharp bends with no backscattering losses. In addition, due to spin-momentum locking, the polaritons with opposite spins (helicities) were transported to different directions. These studies were performed at relatively higher temperatures (200K) and without the need for strong magnetic fields, which make them promising for fundamental studies and device applications. Topological helical polaritons provide a new platform for developing robust and tunable polaritonic spintronic devices for classical and quantum information processing applications.
The Laboratory for Research on the Structure of Matter 