1. valley pseudospin-selective light-exciton integration in multilayered WS2

Su-Hyun Gong

Korea University, Korea

27 April 2021 Tue 4 pm

                                      IBS Center for Theoretical Physics of Complex Systems (PCS), Administrative Office (B349), Theory Wing, 3rd floor

                                      Expo-ro 55, Yuseong-gu, Daejeon, South Korea, 34126 Tel: +82-42-878-8633                     

The emergence of transition metal dichalcogenides (TMD) layers has sparked significant research interest and led to the rapid development of valleytronics. A monolayer of TMD materials has direct bandgaps consisting of two (energy-degenerate) valleys at the corners of the Brillouin zone (K, K’), which provide an opportunity to manipulate the additional degree of freedom, so called the valley degree of freedom. And valley information can be optically addressed and detected using the spin angular momentum of light, due to their valley-dependent optical selection rule. However, the interaction between light and a TMD layer is intrinsically weak due to the huge mismatch between wavelength and the layer thickness (400–1500 nm vs. <1 nm). It is generally believed that additional photonic structures such as external cavity are necessary to increase and control light-matter coupling in a TMD layer. Unfortunately, these additional structures with a linearly polarized optical mode easily spoil valley pseudospin information making it difficult to exploit the full potential of TMD layers. In this talk, the valley-selective exciton–light coupling in a TMD layer will be discussed. In weak coupling regime, we demonstrated directional emission of valley-polarized exciton into plasmonic eigenstates of a silver nanowire. A plasmonic nanowire provides a high degree of local transverse optical spin, and its handedness is locked to the propagation direction of the mode. As a result, the emission from the two different valleys of TMDs material will couple to the plasmonic modes propagating in opposite directions. In strong coupling regime, we investigated coherent coupling between exciton and photon in a thick TMD layer. We found out that these intrinsic exciton polariton in a TMD layer can carry valley information of exciton. Valley-dependent exciton–light coupling offers a novel platform for realization of valley transport even at room temperature without any magnetic fields. And these results pave the way for exploiting a valley pseudospin in integrated valleytronics devices using nanophotonics structures.