Doping Tunable CDW Phase Transition in Bulk 1T-ZrSe2

Abstract

Tunable electronic properties in transition metal dichalcogenides (TMDs) are essential to further their use in device applications. Here, we present a comprehensive scanning tunneling microscopy and spectroscopy study of a doping-induced charge density wave (CDW) in semiconducting bulk 1T-ZrSe₂. We find that atomic impurities that locally shift the Fermi level (E_F) into the conduction band trigger a CDW reconstruction concomitantly to the opening of a gap at E_F. Our findings shed new light on earlier photoemission spectroscopy and theoretical studies of bulk 1T-ZrSe₂ and provide local insight into the electron-doping-mediated CDW transition observed in semiconducting TMDs.

Keywords: Charge Density Wave; Scanning Tunneling Microscopy; Scanning Tunneling Spectroscopy; Tunability.

Figure 1

30 × 30 nm² STM topography of the same region of ZrSe₂ measured at (a) +400 mV, (b) −400 mV, and (c) −1.1 V bias. The insets show the corresponding Fourier transforms. (d) Topography in (a) with overlaid inverse Fourier transforms restricted to the blue and red areas of the FTs in (a) and (b). (e) Trace from the Γ-point to the Bragg peaks as a function of energy averaged along the dashed lines in the FTs (no data are available near E_F). The green dashed line marks the Bragg peak, the blue one marks the CDW peak, and the red dotted lines mark two dispersing QPI features. (f) Topography in (c) with overlaid inverse Fourier transforms restricted to the blue and red areas of the FTs in (a) and (b). The white arrows indicate selected hole-doping defects, and the blue stars indicate the electron-doping defects visible only at high negative bias.

Figure 2

(a) normalized STS map at −9 mV revealing CDW modulations. (b) dI/dV(V) map as a function of position and energy averaged along the Y direction at each position X over the white rectangle in (a), showing the CDW contrast inversion across E_F.

Figure 3

Two averaged dI/dV(V) spectra on a log scale from a grid with different set point bias, −300 and +600 mV for (a) and (b), respectively. The small inserts in each graph show conceptual sketches of the corresponding tip–sample distance.

Figure 4

CDW modulation amplitude versus spectroscopic signal near E_F. (a) CDW modulation amplitude along the black line in the inset CITS map. (b) Gray-scale plot of the dI/dV(V) spectra measured along the same line as panel (a). (c) Normalized dI/dV(V) spectra averaged over the boxes with corresponding color in panel (b).