Robust room temperature valley polarization in monolayer and bilayer WS2. Issue 11 (1st March 2016)

• Record Type: Journal Article
• Authors: Nayak, Pramoda K.; Lin, Fan-Cheng; Yeh, Chao-Hui; Huang, Jer-Shing; Chiu, Po-Wen
• Is Part Of: Nanoscale. Volume 8:Issue 11(2016)
• Page Start: 6035
• Page End: 6042
• Publication Date: 2016-03-01
• Subjects: Nanoscience -- Periodicals; Nanotechnology -- Periodicals; 620.505
• DOI: 10.1039/c5nr08395h
• Languages: English
• ISSNs: 2040-3364

Abstract

Abstract : Robust room temperature valley polarization in monolayer and bilayer WS2 using excitation slightly smaller than the ground state excitation energy. Abstract : We report robust room temperature valley polarization in chemical-vapor-deposition (CVD) grown monolayer and bilayer WS2 via polarization-resolved photoluminescence measurements using excitation below the bandgap. We show that excitation with energy slightly below the bandgap of the multi-valleyed transition metal chalcogenides can effectively suppress the random redistribution of excited electrons and, thereby, greatly enhance the efficiency of valley polarization at room temperature. Compared to mechanically exfoliated WS2, our CVD grown WS2 films also show enhancement in the coupling of spin, layer and valley degree of freedom and, therefore, provide improved valley polarization. At room temperature, using below-bandgap excitation and CVD grown monolayer and bilayer WS2, we have reached a record-high valley polarization of 35% and 80%, respectively, exceeding the previously reported values of 10% and 65% for mechanically exfoliated WS2 layers using resonant excitation. This observation provides a new direction to enhance valley control at room temperature.