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Author: Yilei Li
Requested Type: Oral
Submitted: 2015-04-11 20:35:45

Co-authors: A. Chernikov, Y. Rao, K. F. Mak, X. Zhang, Y. You, A. Rigosi, H. M. Hill, A. M. van der Zande, D. A. Chenet, S. Wang, E. Shih, C. R. Dean, J. Hone, T. F. Heinz

Contact Info:
Columbia University
538 West 120th Street
New York, NY   10027
USA

Abstract Text:
In this paper, we present results for the linear and second-order nonlinear optical response of atomically thin transition metal dichalcogenides (TMDCs). To determine linear optical response, we measured the optical reflectance of a number of TMDC monolayers, including MoSe2, MoS2, WSe2 and WS2. The complex optical sheet conductivity of the TMDC monolayers is obtained through a Kramers-Kronig constrained analysis of the optical spectra. The sheet conductivity provides complete information to predict the linear optical response of the thin layers in a defined dielectric environment.
Symmetry plays a critical role in determining the second-order nonlinear optical response of a crystal system. We show that the second-harmonic (SH) signal from monolayer and odd layers of TMDC is dramatically enhanced comparing to the bulk crystals because of the breaking of inversion symmetry. Restoration of inversion symmetry in even layers is revealed through a strong suppression of the SH signal. For odd layers with large SH response, the SH signal intensity is modulated with a six-fold symmetry by in-plane rotation of the atomically thin crystal. The pattern is consistent with the underlying symmetry group of the crystal and provides a convenient tool to determine the orientation of the crystallographic axes.

Comments:
The submitted paper covers topics in both Category 3.0 and Category 4.0