Visualizing the Anomalous Charge Density Wave States in Graphene/NbSe2 Heterostructures

Yu Chen; Lishu Wu; Hai Xu; Chunxiao Cong; Si Li; Shun Feng; Hongbo Zhang; Chenji Zou; Jingzhi Shang; Shengyuan A Yang; Kian Ping Loh; Wei Huang; Ting Yu

doi:10.1002/adma.202003746

Visualizing the Anomalous Charge Density Wave States in Graphene/NbSe₂ Heterostructures

Adv Mater. 2020 Nov;32(45):e2003746. doi: 10.1002/adma.202003746. Epub 2020 Oct 1.

Authors

Yu Chen^{1

2}, Lishu Wu², Hai Xu^{3

4

5}, Chunxiao Cong^{6

7}, Si Li⁸, Shun Feng², Hongbo Zhang², Chenji Zou², Jingzhi Shang^{1

2}, Shengyuan A Yang⁸, Kian Ping Loh³, Wei Huang^{1

9}, Ting Yu²

Affiliations

¹ Shaanxi Institute of Flexible Electronics (SIFE), Northwestern Polytechnical University (NPU), Xi'an, 710129, China.
² Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, 637371, Singapore.
³ Department of Chemistry, National University of Singapore, Singapore, 117543, Singapore.
⁴ Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Science, Changchun, 130033, China.
⁵ Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing, 100040, China.
⁶ State Key Laboratory of ASIC and System, School of Information Science and Technology, Fudan University, Shanghai, 200433, China.
⁷ Academy for Engineering and Technology, Fudan University, Shanghai, 200433, China.
⁸ Research Laboratory for Quantum Materials, Singapore University of Technology and Design, Singapore, 487372, Singapore.
⁹ Key Laboratory of Flexible Electronics (KLOFE) & Institute of Advanced Materials (IAM), Nanjing Tech University (NanjingTech), Nanjing, 211800, China.

PMID: 33002238
DOI: 10.1002/adma.202003746

Abstract

Metallic layered transition metal dichalcogenides (TMDs) host collective many-body interactions, including the competing superconducting and charge density wave (CDW) states. Graphene is widely employed as a heteroepitaxial substrate for the growth of TMD layers and as an ohmic contact, where the graphene/TMD heterostructure is naturally formed. The presence of graphene can unpredictably influence the CDW order in 2D CDW conductors. This work reports the CDW transitions of 2H-NbSe₂ layers in graphene/NbSe₂ heterostructures. The evolution of Raman spectra demonstrates that the CDW phase transition temperatures (T_CDW ) of NbSe₂ are dramatically decreased when capped by graphene. The induced anomalous short-range CDW state is confirmed by scanning tunneling microscopy measurements. The findings propose a new criterion to determine the T_CDW through monitoring the line shape of the A_1g mode. Meanwhile, the 2D band is also discovered as an indicator to observe the CDW transitions. First-principles calculations imply that interfacial electron doping suppresses the CDW states by impeding the lattice distortion of 2H-NbSe₂ . The extraordinary random CDW lattice suggests deep insight into the formation mechanism of many collective electronic states and possesses great potential in modulating multifunctional devices.

Keywords: 2D transition metal dichalcogenides; anomalous charge density wave; graphene/NbSe2 heterostructures; interfacial electron doping; phase transitions.

Abstract

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