Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Revealing Charge Transfer in Defect-Engineered 4H$_\mathrm{b}$-TaS$_2$

Siavash Karbasizadeh, Wooin Yang, Wonhee Ko, Haidong Zhou, An-Ping Li, Tom Berlijn, Sai Mu

Abstract

We present a comprehensive first-principles investigation of defects in 4$H_b$-TaS$_2$. In this layered transition metal dichalcogenide, charge transfer between alternating Mott-insulating 1T and metallic 1H layers gives rise to exotic quantum phases such as the Kondo effect and topological superconductivity. Motivated by recent defect manipulation in 4$H_b$-TaS$_2$ via STM, we address their microscopic nature and impact on interlayer charge transfer. To this end, we systematically analyze over 90 defects using large-scale density functional theory (DFT) calculations. Our extensive dataset, compiled from STM simulations, defect formation energies, work functions, and charge transfer, establishes a foundational resource for future theoretical and experimental studies on defect engineering in 4$H_b$-TaS$_2$.

Revealing Charge Transfer in Defect-Engineered 4H$_\mathrm{b}$-TaS$_2$

Abstract

We present a comprehensive first-principles investigation of defects in 4-TaS. In this layered transition metal dichalcogenide, charge transfer between alternating Mott-insulating 1T and metallic 1H layers gives rise to exotic quantum phases such as the Kondo effect and topological superconductivity. Motivated by recent defect manipulation in 4-TaS via STM, we address their microscopic nature and impact on interlayer charge transfer. To this end, we systematically analyze over 90 defects using large-scale density functional theory (DFT) calculations. Our extensive dataset, compiled from STM simulations, defect formation energies, work functions, and charge transfer, establishes a foundational resource for future theoretical and experimental studies on defect engineering in 4-TaS.

Paper Structure

This paper contains 11 sections, 7 equations, 11 figures, 2 tables.

Table of Contents

  1. INTRODUCTION
  2. COMPUTATIONAL METHODOLOGY
  3. RESULTS AND DISCUSSION
  4. Sulfur Vacancies
  5. Defect Identification via STM-DFT Comparison
  6. Interlayer Charge Transfer Modulation
  7. Other Defects
  8. Defect Identification via STM-DFT Comparison
  9. Interlayer Charge Transfer Modulation
  10. Hybridization Effects on Charge Transfer
  11. Conclusion and Outlook

Figures (11)

  • Figure 1: (a) Bulk 4$H_b$-TaS$_2$ structure from the side. Brown spheres show tantalum, while the yellow spheres show sulfur. (b) Tantalum atoms constructing the star of David. Black arrows show the displacements of the charge density wave distortion.
  • Figure 2: Scanning tunneling microscopy (STM) image of 1T-terminated 4$H_b$-TaS$_2$ at $V_\mathrm{bias}$ of (a) 200 mV, and (b) $-$200 mV. Types 1 and 2 defects are specified using cyan and neon green circles. Both images were measured at a tunneling current of 10 pA. Parts (c)-(f) show magnified images of the defects in both positive and negative biases. We have also used a purple circle to show a different type of defect that does not belong in the type 1 or 2 categories.
  • Figure 3: 1T-TaS$_2$ monolayer from the top. Brown spheres show tantalum, while the yellow spheres show sulfur. The dotted line marks the charge density wave cell considered. The numbers show different lateral positions of sulfur and tantalum atoms with respect to the tantalum in the center of the star of David (Ta1).
  • Figure 4: Simple picture explaining 1T-terminated 4$H_b$-TaS$_2$ STM contrast of type 2 defects and pristine SoD sites at positive and negative biases, in terms of electron doping Hubbard bands. 1T-TaS$_2$ is a Mott insulator, in pristine 4$H_b$-TaS$_2$ electrons are doped from 1T to 1H, and in the presence of type 2 defect, an electron is doped in 1T, restoring the Mott insulating state. The green dashed line shows the Fermi level.
  • Figure 5: Scanning tunneling microscopy simulations of the 1T/1H bilayer (a) without defects and with (c) $V_\mathrm{S1}^\mathrm{1H(top)}$, (e) $V_\mathrm{S1}^\mathrm{1T(top)}$, (g) $V_\mathrm{S1}^\mathrm{1T(bottom)}$, and (i) O$_\mathrm{S3}^\mathrm{1T(top)}$ at a bias voltage of $-200$ mV. Panels (b), (d), (f), (h), and (j) show the corresponding simulations for the same configurations at $+200$ mV. The red star and blue circle mark the Star-of-David cluster and the lateral position of the defect, respectively.
  • ...and 6 more figures