Anisotropic Collective Charge Excitations in Quasimetallic 2D Transition-Metal Dichalcogenides

Chi Sin Tang; Xinmao Yin; Ming Yang; Di Wu; Jing Wu; Lai Mun Wong; Changjian Li; Shi Wun Tong; Yung-Huang Chang; Fangping Ouyang; Yuan Ping Feng; Shi Jie Wang; Dongzhi Chi; Mark B H Breese; Wenjing Zhang; Andrivo Rusydi; Andrew T S Wee

doi:10.1002/advs.201902726

Anisotropic Collective Charge Excitations in Quasimetallic 2D Transition-Metal Dichalcogenides

Adv Sci (Weinh). 2020 Apr 16;7(10):1902726. doi: 10.1002/advs.201902726. eCollection 2020 May.

Authors

Chi Sin Tang^{1

2}, Xinmao Yin^{1

3}, Ming Yang⁴, Di Wu^{5

6}, Jing Wu⁴, Lai Mun Wong⁴, Changjian Li⁷, Shi Wun Tong⁴, Yung-Huang Chang⁸, Fangping Ouyang⁶, Yuan Ping Feng¹, Shi Jie Wang⁴, Dongzhi Chi⁴, Mark B H Breese^{1

3}, Wenjing Zhang⁵, Andrivo Rusydi^{1

3}, Andrew T S Wee^{1

2}

Affiliations

¹ Department of Physics Faculty of Science National University of Singapore S12 Science Drive 3 Singapore 117551 Singapore.
² NUS Graduate School for Integrative Sciences and Engineering National University of Singapore 21 Lower Kent Ridge Singapore 119077 Singapore.
³ Singapore Synchrotron Light Source (SSLS) National University of Singapore 5 Research Link Singapore 117603 Singapore.
⁴ Institute of Materials Research and Engineering (IMRE) ASTAR (Agency for Science, Technology and Research) 2 Fusionopolis Way, Innovis Singapore 138634 Singapore.
⁵ International Collaborative Laboratory of 2D Materials for Optoelectronics Science and Technology Shenzhen University Shenzhen 518060 China.
⁶ School of Physics and Electronics Central South University No. 932, South Lushan Road Changsha Hunan 410083 China.
⁷ Department of Materials Science & Engineering National University of Singapore 9 Engineering Drive 1 Singapore 117575 Singapore.
⁸ Bachelor Program in Interdisciplinary Studies National Yunlin University of Science and Technology 123 University Road, Section 3 Douliou Yunlin 64002 Taiwan.

Abstract

The quasimetallic 1T' phase 2D transition-metal dichalcogenides (TMDs) consist of 1D zigzag metal chains stacked periodically along a single axis. This gives rise to its prominent physical properties which promises the onset of novel physical phenomena and applications. Here, the in-plane electronic correlations are explored, and new mid-infrared plasmon excitations in 1T' phase monolayer WSe₂ and MoS₂ are observed using optical spectroscopies. Based on an extensive first-principles study which analyzes the charge dynamics across multiple axes of the atomic-layered systems, the collective charge excitations are found to disperse only along the direction perpendicular to the chains. Further analysis reveals that the interchain long-range coupling is responsible for the coherent 1D charge dynamics and the spin-orbit coupling affects the plasmon frequency. Detailed investigation of these charge collective modes in 2D-chained systems offers opportunities for novel device applications and has implications for the underlying mechanism that governs superconductivity in 2D TMD systems.

Keywords: anisotropic charge dynamics; phase transitions; plasmons; spectroscopic ellipsometry; transition‐metal dichalcogenides.