123rd General Meeting of the KCS

Type Oral Presentation
Area Oral Presentation for Young Physical Chemists I
Room No. Room 305+306
Time THU 09:20-09:29
Code PHYS1.O-3
Subject Twist-angle dependent optical second-harmonic generation from transition metal dichalcogenides (TMD) heterostructures
Authors Wontaek Kim, Sunmin Ryu*
Department of Chemistry, Pohang University of Science and Technology, Korea
Abstract Optical second-harmonic generation (SHG) by single and few-layer transition metal dichalcogenides (TMD) is highly efficient and sensitive to their structural symmetry. The SHG signal from artificially-stacked MoS2 bilayers can be understood as a superposition of SHG fields from the individual layers. However, this model has not been verified for TMD heterostructures. Here, we studied the SHG behavior of TMD hetero-bilayers of varying twist angle in comparison with homo-bilayers. When homo-bilayers were rotated over 2pi-azimuth with a fundamental beam normally incident on their basal planes, the polarization-resolved SHG signal exhibited a six-petal pattern with six azimuthal nodes, which agreed with the superposition model. The heterostructures, however, lacked the angular nodes because of an azimuth-independent signal in addition to the six-petal pattern. The fractional contribution of the constant signal was larger for more staggered hetero-bilayers. To explain these results, we propose that the anomaly originates from a non-zero phase difference between SHG fields generated in the individual monolayers. In addition, we show that the degree of the anomaly is sensitive to the fundamental’s wavelength, as the phase depends on photon energy.
E-mail kwt2015@postech.ac.kr