Figure 1

(Color online) The average (undistorted) crystal structure of ${\text{CeTe}}_3$ consisting of corrugated CeTe slabs and Te layers, where Te atoms are separated by $3.1\text{Å}$ in a square net. The side view shows two complete unit cells, with the unit repeated along the $b$ axis. The top view shows the surface Te net exposed upon cleaving the crystal. The first subsurface layers of Ce and Te atoms are indicated. Taking into account atomic relaxation, with respect to the $b$ direction (perpendicular to the layers), the subsurface Ce lattice is $2.53\text{Å}$ below the surface Te net and the subsurface Te lattice is $3.44\text{Å}$ below the Te net.Reuse & Permissions

Figure 2

(Color online) (a) A $10\times 10\text{nm}$ real-space STM image of the Te net obtained at 77 K, showing both Te atoms and CDW modulations oriented at $45°$ to the net. The image is the average of four images that were obtained consecutively, in constant-current mode, at a sample bias of 100 mV and tunneling current of 0.6 nA; no image processing or filtering of the data was performed. The bright irregular features indicate surface contamination. The expanded image on the right includes a square grid as a guide to the eyes; a Te atom is located at each intersection. The gray lines on the left mark the locations of the CDW maxima. (b) A simple simulation of the STM image intended to address the apparent irregular spacing of the CDW feature. Top: a square two-dimensional sinusoidal lattice of wavelength $a_0=0.31\text{nm}$ to represent the Te net. It is superimposed with a larger lattice, scaled by $\sqrt{2}$ and rotated by $45°$ to account for the subsurface structure. Middle: a one-dimensional sine wave of wavelength 1.60 nm to represent the CDW. Bottom: the sum of the simulated lattice and CDW. We see that each CDW wavelength forms a distinct pattern which is qualitatively different from the neighboring stripes. The gray lines mark the actual CDW maxima.Reuse & Permissions

Figure 3

(Color online) (a) The Fourier transform of the low temperature STM data. Enhanced noise along the vertical axis is an artifact due to the scan direction. Horizontal and vertical axes are wave-vector components $k_x$ and $k_y$. The square Te net gives rise to four distinct peaks (L). Peaks at $45°$ to Te net are consistent with the CDW peaks. The CDW peak $q_{\text{CDW}}$, as well as peak $q_{\text{atom}}$, which is consistent with underlying atomic structure, are labeled. (b) Subset of the data from the Fourier transform along a path from the origin in the direction of the CDW. Noise in the Fourier transform becomes significantly larger near the origin. This is due to the impurities present in the real-space data. As the guide to the eyes, the dashed line indicates the background noise.Reuse & Permissions

Figure 4

(Color online) (a) STM topography of ${\text{CeTe}}_3$ at room temperature in ambient conditions with a sample bias of $-800\text{mV}$, the same used in Fig. 2(a) of Ref. 10. The current set point was $-0.14\text{nA}$, which was necessary to achieve quality comparable to that of Ref. 10. We do not observe evidence of dimerizations, in contrast to the work of Fang et al. with the related material, ${\text{TbTe}}_3$. Lower quality images at $-0.05\text{nA}$ (the reported current for Ref. 10) also lacked evidence of dimerizations. The image shown is raw data, aside from line by line subtraction and the manual removal of an artifact caused by the controller software. (b) Low-pass Fourier filtered image of the same data in (a). Data shown are those below $\left|k\right|=26{\text{nm}}^{-1}$. The image is given in high contrast for comparison with Ref. 10.Reuse & Permissions

Figure 5

Local DOS around the Fermi level for ${\text{CeTe}}_3$. The Fermi level corresponds to zero bias voltage. The estimated CDW gap size in ${\text{CeTe}}_3$ is about 360 meV, as indicated by vertical arrows. The spectroscopy was carried out when the tip was located directly above a Te atom. The effect of thermal smearing of the data is approximately $3.5k_{B}T\approx 25\text{meV}$ at 77 K temperature; hence it is not significant over the plotted range. Inset: expanded view of $dI/dV$ near the Fermi level is shown to enhance the visibility of the subtle edges we identify as the CDW energy gap (again indicated by vertical arrows).Reuse & Permissions

Figure 6

To simulate the STM image, we give the contour plot of the charge density projected onto a plane at $3.0\text{Å}$ above the surface, in the energy range of 0.0–0.1 eV. The brighter (white) spots come from the surface Te. The subsurface Ce atoms contribute more to the charge density than the subsurface Te atoms. The Fermi level $\left(E_F\right)$ corresponds to 0.0 eV. Moreover, the subsurface modulation, considering only the regions between surface Te, is of comparable magnitude to the signal from the surface Te net.Reuse & Permissions

Figure 7

(Color online) The only significant contribution to the DOS near $E_F$ comes from the surface $\text{Te}{p}_x$ and $p_y$ states. (a) Partial DOS associated with the $p_x$ and $p_y$ orbitals of the surface Te atoms. The flat DOS near $E_F$ is characteristic to the CDW systems. (b) The $p_z$ orbital of the surface Te is occupied and located mostly below $E_F$. [(c) and (d)] The $p$-states of the subsurface Te atoms are occupied because the trivalent Ce provides two electrons within the Ce-Te slab.Reuse & Permissions

Figure 8

(Color online) Spin-polarized partial DOS associated with the subsurface Ce atom. The peak at $-2.5\text{eV}$ in the spin-up DOS corresponds to one occupied $f$ level while the peaks between 3.0–5.0 eV (spin-up and spin-down) represent the 13 unoccupied $f$ states. The inset shows that the DOS near $E_F$ is nonzero.Reuse & Permissions