Chemical pressure and hidden one-dimensional behavior in rare-earth tri-telluride charge-density wave compounds

We report on the first optical measurements of the rare-earth tri-telluride charge-density wave systems. Our data, collected over an extremely broad spectral range, allow us to observe both the Drude component and the single-particle peak, ascribed to the contributions due to the free charge carriers and to the charge-density wave gap excitation, respectively. The data analysis displays a diminishing impact of the charge-density wave condensate on the electronic properties with decreasing lattice constant across the rare-earth series. We propose a possible mechanism describing this behavior and we suggest the presence of a one-dimensional character in these two-dimensional compounds. We also envisage that interactions and umklapp processes might play a relevant role in the formation of the charge-density wave state in these compounds.

Figure 1

$R\left(\omega \right)$ at room temperature of $R{\mathrm{Te}}_3$ ($R$ is La, Ce, Nd, Sm, Gd, Tb, and Dy). The inset shows a blow up of the $R\left(\omega \right)$ in the energy range between 0 and $10000{\mathrm{cm}}^{-1}$.

Figure 2

Room temperature ${\sigma }_1\left(\omega \right)$ of $R{\mathrm{Te}}_3$ ($R$ is La, Ce, Nd, Sm, Gd, Tb, and Dy). Arrows mark the position of the SP peak for each compound (see text). Inset: Drude-Lorentz fit for ${\mathrm{DyTe}}_3$, showing the experimental data, the fitted curve, and the Drude and the Lorentz components.

Figure 3

Plasma frequency (a) and single-particle peak frequency (b) as a function of the in-plane lattice constant (Ref. 12). The rare-earth atom for each compound is shown in the plot. The solid lines are guides to eyes.

Figure 4

Ratios $\Phi ={\omega }_P^2∕({\omega }_P^2+S_{SP}^2)$ (indicating the fraction of the ungapped FS) and $n_{CDW}∕n_{NS}$ as a function of the in-plane lattice constant (Ref. 12). The left and right scales differ by a factor of 2. The rare-earth atom for each compound is shown in the plot. The solid line is a guide to eyes.

Figure 5

${\sigma }_1\left(\omega \right)$ of $R{\mathrm{Te}}_3$ ($R$ is La, Ce, Nd, Sm, Gd, Tb, and Dy) plotted on a bilogarithmic scale. The $y$-axis logarithmic scale is vertically shifted for the sake of clarity. The scale is the same for all samples and the scale offset is shown for each spectrum. The solid lines are power-law fits to the data (the exponents are given in the figure).