Electrically Tunable and Dramatically Enhanced Valley‐Polarized Emission of Monolayer WS<sub>2</sub> at Room Temperature with Plasmonic Archimedes Spiral Nanostructures
Wei‐Hsiang Lin, Pin Chieh Wu, Hamidreza Akbari, George R. Rossman, N.-C. Yeh, Harry A. Atwater
Abstract
Abstract Monolayer transition metal dichalcogenides (TMDs) have intrinsic valley degrees of freedom, making them appealing for exploiting valleytronic applications in information storage and processing. WS 2 monolayer possesses two inequivalent valleys in the Brillouin zone, each valley coupling selectively with a circular polarization of light. The degree of valley polarization (DVP) under the excitation of circularly polarized light (CPL) is a parameter that determines the purity of valley polarized photoluminescence (PL) of monolayer WS 2 . Here efficient tailoring of valley‐polarized PL from monolayer WS 2 at room temperature (RT) through surface plasmon–exciton interactions with plasmonic Archimedes spiral (PAS) nanostructures is reported. The DVP of WS 2 at RT can be enhanced from <5% to 40% and 50% by using 2 turns (2T) and 4 turns (4T) of PAS, respectively. Further enhancement and control of excitonic valley polarization is demonstrated by electrostatically doping monolayer WS 2 . For CPL on WS 2 –2TPAS heterostructures, the 40% valley polarization is enhanced to 70% by modulating the carrier doping via a backgate, which may be attributed to the screening of momentum‐dependent long‐range electron–hole exchange interactions. The manifestation of electrically tunable valley‐polarized emission from WS 2 –PAS heterostructures presents a new strategy toward harnessing valley excitons for application in ultrathin valleytronic devices.