Localization of Conduction Electrons by Fe, Co, and Ni in 1T-TaS2 and 1T-TaSe2

Abstract

$1T-M_x{\mathrm{Ta}}_{1-x}{\mathrm{S}}_2$ or $1T-M_x{\mathrm{Ta}}_{1-x}{\mathrm{Se}}_2$ with $M=\mathrm{F}\mathrm{e},\mathrm{C}\mathrm{o},\mathrm{o}\mathrm{r}\mathrm{N}\mathrm{i}$ shows large increases in resistivity at low temperatures when $\frac{1}{3}>x>~x_c$ ($x_c\approx 0.02$ for the disulfides, and 0.15 for the diselenides). We suggest that this increase is due to Anderson localization of the conduction electrons by the random potential of $M$. However, in contrast to the usual impurity state in metals, the presence of a charge-density wave makes this potential temperature dependent and long ranged.