Observation of Electronic Strong Correlation in ${\mathrm{VTe}}_{2}\text{-2}\sqrt{3}\ifmmode\times\else\texttimes\fi{}2\sqrt{3}$ Monolayer

Observation of Electronic Strong Correlation in ${VTe}_{2} -2 \sqrt{3} \times 2 \sqrt{3}$ Monolayer

Wei-Min Zhao, Wenjun Ding, Qi-Wei Wang, Yu-Xin Meng, Li Zhu, Zhen-Yu Jia, Wenguang Zhu, and Shao-Chun Li

Phys. Rev. Lett. 131, 086501 – Published 21 August 2023

Abstract

Strong electron correlation under two-dimensional limit is intensely studied in the transition metal dichalcogenides monolayers, mostly within their charge density wave (CDW) states that host a star of David period. Here, by using scanning tunneling microscopy and spectroscopy and density functional theory calculations with on-site Hubbard corrections, we study the ${VTe}_{2}$ monolayer with a different $2 \sqrt{3} \times 2 \sqrt{3}$ CDW period. We find that the dimerization of neighboring Te-Te and V-V atoms occurs during the CDW transition, and that the strong correlation effect opens a Mott-like full gap at Fermi energy ( $E_{F}$ ). We further demonstrate that such a Mott phenomenon is ascribed to the combination of the CDW transition and on-site Coulomb interactions. Our work provides a new platform for exploring Mott physics in 2D materials.

Received 22 December 2022
Revised 9 July 2023
Accepted 18 July 2023

DOI:https://doi.org/10.1103/PhysRevLett.131.086501

Physics Subject Headings (PhySH)

Charge density waves Electronic structure

Monolayer films Strongly correlated systems Transition metal dichalcogenides

Scanning tunneling microscopy Scanning tunneling spectroscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Wei-Min Zhao¹, Wenjun Ding², Qi-Wei Wang¹, Yu-Xin Meng¹, Li Zhu¹, Zhen-Yu Jia¹, Wenguang Zhu^2,3, and Shao-Chun Li ^1,3,4,5,*

¹National Laboratory of Solid State Microstructures, School of Physics, Nanjing University, Nanjing 210093, China
²International Center for Quantum Design of Functional Materials (ICQD), Hefei National Research Center for Physical Sciences at the Microscale, Department of Physics, University of Science and Technology of China, Hefei 230026, China
³Hefei National Laboratory, Hefei 230088, China
⁴Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
⁵Jiangsu Provincial Key Laboratory for Nanotechnology, Nanjing University, Nanjing 210093, China

^*Corresponding author: scli@nju.edu.cn

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Vol. 131, Iss. 8 — 25 August 2023

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Figure 1
(a) Atomically resolved STM image ( $9 \times 9 {nm}^{2}$ ) taken on the $2 \sqrt{3} \times 2 \sqrt{3} {VTe}_{2}$ monolayer. $U = + 17 mV$ , $I_{t} = 100 pA$ . Inset: Fast Fourier transform (FFT) image. The blue and red circles mark the Bragg and CDW vectors, respectively. (b) Atomically resolved STM image ( $5 \times 5 {nm}^{2}$ ) taken on the ${VTe}_{2}$ monolayer. $U = - 30 mV$ , $I_{t} = 100 pA$ . The black ellipses enclose the Te-Te dimers. (c) Enlargement of an image of (b) with an overlaid ideal atomic lattice. In atomic model of ${VTe}_{2}$ monolayer, the top Te atoms and middle V atoms are labeled by brown and blue balls, while the bottom Te atoms are not shown for clarity. The black lines mark the truncated triangle-shaped clustered structures of the $2 \sqrt{3} \times 2 \sqrt{3} CDW$ period. The colored circles (red, orange, blue, and black) mark the four groups of topmost Te atoms (A, B, C, and D) within a CDW supercell. (d) DFT calculated $2 \sqrt{3} \times 2 \sqrt{3} CDW$ phase of ${VTe}_{2}$ monolayer. The bond lengths between Te atoms and V atoms are labeled by $l$ and $l^{'}$ .
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Figure 2
(a) Typical $d I / d V$ spectrum taken on the $2 \sqrt{3} \times 2 \sqrt{3} {VTe}_{2}$ monolayer, showing four characteristic peaks as labeled by $V_{1}$ ( $\sim - 125 mV$ ), $V_{2}$ ( $\sim - 460 mV$ ), $C_{1}$ ( $\sim + 220 mV$ ), and $C_{2}$ ( $\sim + 480 mV$ ), respectively. $U = + 300 mV$ , $I_{t} = 200 pA$ . (b) Small-range $d I / d V$ spectrum showing a full gap feature near Fermi energy ( $E_{F}$ ). The $d I / d V$ intensity is completely suppressed to zero at $E_{F}$ . $U = + 200 mV$ , $I_{t} = 200 pA$ . (c) $d I / d V$ spectra taken at positions of A, B, C, and D within a CDW supercell. $U = + 300 mV$ , $I_{t} = 200 pA$ . The black arrow marks the position of the IGS that is localized at the A position. Inset: Atomic model of the top Te atoms with the colored balls (red, orange, blue, and black) representing the positions (A, B, C, and D) of the top Te atoms, as defined in Fig. 1. (d) Spatially resolved $d I / d V$ spectra taken along the black arrowed line in the upper panel image. $U = + 300 mV$ , $I_{t} = 200 pA$ . (e) Line-cut profiles extracted at three bias voltages as marked by the three colored triangles in (d).
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Figure 3
(a) STM topographic image ( $12 \times 12 {nm}^{2}$ ) taken on the $2 \sqrt{3} \times 2 \sqrt{3} {VTe}_{2}$ monolayer with a low K coverage. The $2 \sqrt{3} \times 2 \sqrt{3}$ CDW order is persistent and clearly identifiable. The center of each adsorbed K atom is marked with a gray ball. More topographic images taken at various K coverages can be found in Fig. S7 in the Supplemental Material [24]. (b) $d I / d V$ spectra taken on the K-occupied site (the hollow site between position A and B) at $\sim 0.1 1 ML$ and the equivalent site on the pristine ${VTe}_{2}$ surface, respectively. $U = + 300 mV$ , $I_{t} = 200 pA$ . (c) $d I / d V$ spectra taken on the positions of $C / D$ that are away from the K-occupied sites at various K coverages. $U = + 300 mV$ , $I_{t} = 200 pA$ . The positions of $C_{1}$ and IGS are marked by the vertical short lines and triangles, respectively. The K coverage is defined as the number of potassium atoms per CDW supercell.
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Figure 4
(a) DFT-calculated band structures of the prototype 1T phase of ${VTe}_{2}$ monolayer, at $U = 0 eV$ , in the nonmagnetic state. (b),(c) Band structures of the $2 \sqrt{3} \times 2 \sqrt{3}$ CDW phase of ${VTe}_{2}$ monolayers in the nonmagnetic state without and with U corrections. The lower panels of (a)–(c) are the corresponding DFT-calculated DOS results.
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Physical Review Letters

Observation of Electronic Strong Correlation in VTe2-23×23 Monolayer

Wei-Min Zhao, Wenjun Ding, Qi-Wei Wang, Yu-Xin Meng, Li Zhu, Zhen-Yu Jia, Wenguang Zhu, and Shao-Chun Li

Phys. Rev. Lett. 131, 086501 – Published 21 August 2023

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Observation of Electronic Strong Correlation in ${VTe}_{2} -2 \sqrt{3} \times 2 \sqrt{3}$ Monolayer