Thickness-dependent electronic structure in layered ${\mathrm{ZrTe}}_{5}$ down to the two-dimensional limit

Thickness-dependent electronic structure in layered ${ZrTe}_{5}$ down to the two-dimensional limit

W. Z. Zhuo, B. Lei, C. S. Zhu, Z. L. Sun, J. H. Cui, W. X. Wang, Z. Y. Wang, T. Wu, J. J. Ying, Z. J. Xiang, and X. H. Chen

Phys. Rev. B 106, 085428 – Published 30 August 2022

Abstract

Zirconium pentatelluride ( ${ZrTe}_{5}$ ) has recently attracted intense research interest, mainly due to its potential topological nontriviality and the extraordinary quantum phenomena it displays. As an exemplary layered compound, ${ZrTe}_{5}$ is expected to exhibit thickness-sensitive physical properties that vary with thinning towards the two-dimensional (2D) limit, which has not been thoroughly investigated yet. In this work, we successfully prepare sizable ${ZrTe}_{5}$ thin flakes down to the monolayer for the first time. By examining the evolution of magnetotransport properties and the Shubnikov–de Haas effect in ${ZrTe}_{5}$ flakes with various layer numbers, we reveal a pronounced thickness dependence of the electronic structure of ${ZrTe}_{5}$ characterized by a downward shift of the Fermi level as large as ∼160 meV upon thickness reduction from bulk to two-unit cells (four atomic layers). Furthermore, an external electric field effectively modifies the magnetoresistance and quantum oscillation frequency in the few-layered ${ZrTe}_{5}$ . Our study proves that ${ZrTe}_{5}$ thin flake can be an excellent platform for exploring the novel properties proposed for 2D topological materials as well as their tunability.

Received 2 June 2022
Revised 5 August 2022
Accepted 11 August 2022

DOI:https://doi.org/10.1103/PhysRevB.106.085428

Physics Subject Headings (PhySH)

Electrical properties Electronic structure Fermi surface

2-dimensional systems Topological materials

Quantum oscillation techniques

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

W. Z. Zhuo¹, B. Lei¹, C. S. Zhu¹, Z. L. Sun¹, J. H. Cui¹, W. X. Wang¹, Z. Y. Wang¹, T. Wu¹, J. J. Ying¹, Z. J. Xiang^1,*, and X. H. Chen ^1,2,3,†

¹Department of Physics, and Key Laboratory of Strongly-Couple Quantum Matter Physics, Chinese Academy of Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China
²Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
³CAS Center for Excellence in Quantum Information and Quantum Physics, Hefei, Anhui 230026, China

^*Correspondence and requests for materials should be addressed: zijixiang@ustc.edu.cn
^†chenxh@ustc.edu.cn

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Vol. 106, Iss. 8 — 15 August 2022

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Figure 1
${ZrTe}_{5}$ thin-flake device fabrication. (a) Crystal structure of ${ZrTe}_{5}$ . (b) Optical image of the exfoliated ${ZrTe}_{5}$ thin flakes on a ${Al}_{2} O_{3}$ film (thickness ∼80 nm) attached to PDMS film. (c) Optical transmittance as a function of the number of layers. The transmittance (orange dots) follows the Beer-Lambert law (blue line, see main text). The transmittance is defined as $G_{sample}^{T} / G_{substrate}^{T}$ , where $G_{sample}^{T}$ and $G_{substrate}^{T}$ are the intensities of the transmission (T) through the sample and substrate of the image captured with a CCD camera. (d) optical image of the device with the monolayered ${ZrTe}_{5}$ thin flake serves as the conduction channel.
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Figure 2
Temperature-dependent resistance in ${ZrTe}_{5}$ thin flakes. (a) Evolution of the $T$ -dependent normalized resistance for ${ZrTe}_{5}$ flakes with different thicknesses. (b) The resistance ratio R (2 K)/R (300 K) plotted against flake thickness. Power-law hopping fitting of the temperature-dependent resistance from 2 to 10 K for double-layered sample (c) and monolayered sample (d). The hollow circles are data points. The red lines denote power-law hopping fits.
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Figure 3
Hall resistivity in ${ZrTe}_{5}$ thin flakes. (a) Field dependence of Hall resistivity at representative thicknesses of ${ZrTe}_{5}$ . (b) Thickness-dependent carrier densities at 2 K. Carrier densities are obtained from a two-band model fit in which we assign $n_{1}$ ( $n_{2}$ ) to the density of the carrier branch with higher (lower) mobility. The solid and hollow squares (circles) indicate the electron-type and hole-type carrier densities with higher (lower) mobility, respectively. Inset provides a partially expanded view for $n_{1}$ showing its change from electron-type to hole-type with thickness reducing.
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Figure 4
Magnetoresistance in ${ZrTe}_{5}$ thin flakes. (a) Evolution of the magnetoresistance with the thickness of ${ZrTe}_{5}$ . Inset displays the thickness dependence of MR $(B = 9 T)$ at 2 K. (b) The second field derivative of the MR show quantum oscillations that are periodic in 1/ $B$ (the Shubnikov–de Haas effect). The peaks of the oscillatory resistance are labeled with integer Landau level indices ( $n$ ). Determination of the number $n$ follows the convention that the phase γ takes the value $- 1 < γ < 1$ . (c) Thickness-dependent oscillation frequency and the corresponding extremal cross-sectional area of Fermi surface. The black squares are oscillation frequency and the red circles donate the corresponding extremal cross-sectional area. Inset is a sketch showing the evolution of Fermi level position with the variation of flake thickness. Vertical dashed lines are assumed boundaries for the thickness range over which the Fermi level falls into the Dirac gap.
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Figure 5
Electric-field tunable magnetoresistance and quantum oscillation frequency. (a) Gate voltage-dependent magnetoresistance in ${ZrTe}_{5}$ few-layered sample of 6 L at 2 K with magnetic field applied along the $b$ direction. (b) Evolution of the oscillatory component $Δ R / R$ (0) as a function of inverse magnetic field (1/ $B$ ) with increasing the gate voltage. (c) Gate-voltage-dependent oscillation frequency (black squares) and the corresponding extremal cross-sectional area of Fermi surface (red circles).
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Physical Review B

covering condensed matter and materials physics

Thickness-dependent electronic structure in layered ${ZrTe}_{5}$ down to the two-dimensional limit

W. Z. Zhuo, B. Lei, C. S. Zhu, Z. L. Sun, J. H. Cui, W. X. Wang, Z. Y. Wang, T. Wu, J. J. Ying, Z. J. Xiang, and X. H. Chen

Phys. Rev. B 106, 085428 – Published 30 August 2022

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Physical Review B

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Thickness-dependent electronic structure in layered ZrTe5 down to the two-dimensional limit

W. Z. Zhuo, B. Lei, C. S. Zhu, Z. L. Sun, J. H. Cui, W. X. Wang, Z. Y. Wang, T. Wu, J. J. Ying, Z. J. Xiang, and X. H. Chen

Phys. Rev. B 106, 085428 – Published 30 August 2022

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Thickness-dependent electronic structure in layered ${ZrTe}_{5}$ down to the two-dimensional limit