Our understanding of quantum physics has involved the creation of a wide range of “quasiparticles.” These notional constructs describe emergent phenomena that appear to have the properties of multiple other particles mixed together.
An exciton, for example, is a quasiparticle that acts like an electron bound to an electron hole, or the empty space in a semiconducting material where an electron could be. A step further, an exciton-polariton combines the properties of an exciton with that of a photon, making it behave like a combination of matter and light. Achieving and actively controlling the right mixture of these properties — such as their mass, speed, direction of motion, and capability to strongly interact with one another — is the key to applying quantum phenomena to technology, like computers.
Now, researchers at the University of Pennsylvania’s School of Engineering and Applied Science are the first to create an even more exotic form of the exciton-polariton, one which has a defined quantum spin that is locked to its direction of motion. Depending on the direction of their spin, these helical topological exciton-polaritons move in opposite directions along the surface of an equally specialized type of topological insulator.
Read more at: University of Pennsylvania
On the left, an image of the Agarwal group's device, a single layer of tungsten disulfide (WS2) on a periodically patterned photonic crystal. Strong coupling between the excitons of WS2 with the photonic crystal leads to the formation of exciton-photon polaritons with helical topological properties. On the right, the bright spot is circularly polarized light exciting helical topological exciton-polaritons, which have a particular spin and propagate forward, bending around sharp corners with no backscattering. (Photo Credit: University of Pennsylvania)