STM Studies of ${\mathrm{TbTe}}_3$: Evidence for a Fully Incommensurate Charge Density Wave

We observe unidirectional charge density wave (CDW) ordering on the quasi-2D material ${\mathrm{TbTe}}_3$ with a scanning tunneling microscope at $\sim 6\mathrm{K}$. Our analysis indicates that the CDW is fully incommensurate, with wave vector $q_{\mathrm{CDW}}\approx 0.71\times 2\pi /c$. By imaging at various tip-sample voltages, we highlight effects of the subsurface layer and its effect on the CDW. We also observe an additional (possibly surface) dimerization and $\approx 0.68\times 2\pi /a$ ordering perpendicular to the CDW.

Figure 1

(a) Schematic of band folding and nesting in $R{\mathrm{Te}}_3$. (b) $T\approx 6\mathrm{K}$ topography with voltage bias $+200\mathrm{mV}$, 50 pA current. (c) Average spectrum in the range $\pm 800\mathrm{mV}$. Spectrum also multiplied to show gap structure. Lines indicate maximal gap as measured by ARPES.

Figure 2

Zoomed-in view of topographic scans with 50 pA setpoint current. All units in Å. (a) Topography at $-800\mathrm{mV}$, (b) $-200\mathrm{mV}$. Right half shows locations of the surface Te atoms. (c) $+200\mathrm{mV}$.

Figure 3

(a) Fourier transform of $+200\mathrm{mV}$ topography [Fig. 1a]. $\mathrm{O}=\mathrm{\text{Origin}}$; $\mathrm{E}=\mathrm{Te}$ square lattice (2D BZ); $\mathrm{R}=\mathrm{\text{block}}$ layer (3DBZ). (b) Blue: Line cut from O to R, thru the CDW. Red: same analysis for $-800\mathrm{mV}$ topograph. Amplitude rescaled for clarity. (c) Line cut from the CDW point C to D.

Figure 4

(a) Line scan along the sample ($\mathrm{CDW}+\mathrm{\text{lattice}}$), in groups of 7 unit cells. Blue is one end of the sample, evolving to dark red (other end). (b) Same signal, with atomic features filtered out ($\mathrm{CDW}+\mathrm{\text{distortions}}$), and amplitude multiplied by 2. (c) Main CDW component only.