Nanoscale electronic inhomogeneities in $1T{\text{-TaS}}_{2}$

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Nanoscale electronic inhomogeneities in $1 T {-TaS}_{2}$

B. Campbell, J. V. Riffle, A. de la Torre, Q. Wang, K. W. Plumb, and S. M. Hollen

Phys. Rev. Materials 8, 034002 – Published 6 March 2024

Abstract

We report a set of scanning tunneling microscopy (STM) and spectroscopy (STS) experiments studying native defects in CVT grown $1 T − {TaS}_{2}$ . Six different sample surfaces from four bulk crystals were investigated. Wide area imaging reveals a prevalence of nanometer-scale electronic inhomogeneities due to native defects, with pristine regions interspersed. These inhomogeneities appear in typical as-grown crystals and coexist with a well-formed commensurate charge density wave of $1 T − {TaS}_{2}$ at low temperatures. Electronic inhomogeneities show up both as variations in the apparent height in STM and in the local density of states in STS; the bands can shift by 60 meV and the gap varies by more than 100 meV across inhomogeneities. These inhomogeneities are present in similar concentration across large-scale areas of all samples studied, but do not influence the charge density wave formation on local or global scales. The commensurate charge density wave exhibits long-range order and remains locally intact in the presence of these inhomogeneities.

Received 10 October 2023
Accepted 26 January 2024

DOI:https://doi.org/10.1103/PhysRevMaterials.8.034002

Physics Subject Headings (PhySH)

Charge density waves Point defects

Transition metal dichalcogenides

Scanning tunneling microscopy Scanning tunneling spectroscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

B. Campbell ^1,*, J. V. Riffle^1,*, A. de la Torre ^2,†, Q. Wang ², K. W. Plumb ², and S. M. Hollen ^1,‡

¹Department of Physics and Astronomy, University of New Hampshire, Durham, NH 03824, USA
²Department of Physics, Brown University, Providence, RI, 02912, USA

^*These authors contributed equally.
^†Present address: Department of Physics, Northeastern University, Boston, MA 02115.
^‡shawna.hollen@unh.edu

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Vol. 8, Iss. 3 — March 2024

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Figure 1
STM topographs of the $1 T − {TaS}_{2}$ surface at $T = 10$ K after cleaving in ultrahigh vacuum. (a), (c) Topography showing the C-CDW and atomic resolution [(a) 500 mV, 150 pA; (b) 550 mV, 145 pA]. Insets: magnified view showing resolution of S atoms with lattice overlay (red dots) and star of David C-CDW pattern (dashed white triangles). (b), (d) Fast-Fourier transform (FFT) of images in (a), (c). Blue vector corresponds to $q_{lattice}$ and red vector to $q_{CDW}$ . $| q_{CDW} | = 0.853 \pm 0.03 {nm}^{- 1}$ ( $0.27 \pm 0.12$ rlu) for (b), $| q_{CDW} | = 0.912 \pm 0.11 {nm}^{- 1}$ ( $0.31 \pm 0.25$ rlu) for (d).
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Figure 2
(a) Large area STM topograph showing the C-CDW and apparent height variations (300 mV, 65 pA setpoint). Scale bar is 14 nm. Color range is from 0 nm (black) to 2.92 nm (white). Inset: fast-Fourier transform. FFT scale bar is 1.5 ${nm}^{- 1}$ . (b) Topograph with low-pass filter applied, as indicated by the dashed circle in (a) inset, to bring out the nanoscale apparent height modulations. Color range is from 0 nm to 0.236 nm. (c) Topograph with high pass filter applied, as indicated by the dashed circle in (a) inset, to show the uninterrupted C-CDW. Color range is from 0.1 nm to 0.193 nm. (d) Line cut over white arrow in (a) showing the 1.2 nm periodic modulations of the C-CDW and the additional large-scale structure and amplitude variations created by the larger-scale electronic disorder.
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Figure 3
(a) Reciprocal space map perpendicular to $[0, 0, L]$ centered at $L = 10$ (integration range $δ L \pm = . 04$ r.l.u.). The six satellite peaks correspond to the C-CDW at $T = 80$ K. (b) Transverse cut through a representative C-CDW peak as indicated by the orange dashed line in (a). Dotted red line encodes a Gaussian fit to the data.
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Figure 4
STM topographs showing the C-CDW and defective atomic lattice. (a) $- 500$ mV and 50 pA, and (b) 550 mV and 145 pA. Red arrows indicated regions where the atomic lattice appears disrupted. Dashed yellow circles highlight regions with diffuse apparent height differences, but no lattice disruption.
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Figure 5
(a), (c) STM topographs and (b), (d) dI/dV maps taken at -300 mV and 300 mV, respectively. Scale bar is 5 nm. (e) dI/dV spectroscopy taken on and off the defect between the orange dashed lines in a and c. (f) dI/dV point spectroscopy taken over the white line marked in a and c. Orange, dashed lines denote the boundary of the defect and the x-axis denotes distance along the cut, increasing in the direction of the arrow in a, c. The horizontal, white lines denote slices at $\pm 300$ mV that correspond to the dI/dV maps in (b), (d).
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Figure 6
$16 \times 16$ grid of STS measurements over a $100 \times 100 {nm}^{2}$ area showing nanometer-scale inhomogeneities in gap width and gap center. (a) TM topograph showing the nanometer-scale disorder. (b) Mean LDOS taken over all $16 \times 16$ spectra plotted in blue with standard deviation denoted by the shaded region. The mean gap center is marked by the red vertical, dashed line and the mean gap width is indicated by the red arrows. Mean gap width is $120 \pm 50$ mV and gap centers show variations up to 60mV. (c) Spatial plot of the gap width as defined in methods. Each pixel represents an STS measurement at the center of a $6.25 \times 6.25 {nm}^{2}$ section of (a). (d) Spatial plot of the gap center as defined in methods. Red and blue denote a negative and positive shift, respectively. All scale bars are 20 nm.
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Physical Review Materials

Nanoscale electronic inhomogeneities in 1T-TaS2

B. Campbell, J. V. Riffle, A. de la Torre, Q. Wang, K. W. Plumb, and S. M. Hollen

Phys. Rev. Materials 8, 034002 – Published 6 March 2024

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Nanoscale electronic inhomogeneities in $1 T {-TaS}_{2}$