Optical probing charge density wave and lattice vibration in metallic 2D materials

• Main Author: Chen, Yu
• Other Authors: Yu Ting
• Format: Theses and Dissertations
• Language: English
• Published: 2018
• Subjects: DRNTU::Science::Physics
• Online Access: http://hdl.handle.net/10356/75862
• Institution: Nanyang Technological University

Layered metallic transition metal dichalcogenide (TMD), representing a novel group of two-dimensional (2D) materials, has attracted considerable interest due to its coexistence and competition of collective many-body phenomena, including charge density wave (CDW) and superconductivity. Here, the charge density wave instabilities, phonon vibrations and thermal conductivities of the layered metallic transition metal dichalcogenides have been optically investigated by in situ Raman spectroscopy and scanning tunneling microscope. In the first part, we focus on the investigation and manipulation of CDW orders in 2D metallic TMDs (1T-TaS2 and 1T-TiSe2). Furthermore, the effects of interlayer coupling on the CDW states have been explored in graphene/NbSe2 heterostructures. Finally, the in-plane anisotropic thermal conductivity, which is related to the lattice vibrations, is also revealed in few-layer Td-WTe2 films via micro Raman spectroscopy. In general, our work on these metallic 2D materials opens up a new window for the controllable synthesis of ultrathin CDW materials and demonstrates effective strategies for tuning these many-body states. The observation of in-plane anisotropic thermal conductivity sheds more light on the design of efficient thermal management schemes in the next-generation thermoelectric devices based on the promising 2D TMDs.