Doping-induced Charge-Density-Wave

Doping is a useful method for searching new characters in solids, as we can see in the discoveries of impurity semiconductors and high-temperature superconductors. If a Charge-Density-Wave (CDW) is induced in materials which do not exhibit a CDW, new CDW properties might be brought there. TaSe$_{3}$ exhibits no CDW transition but a superconductivity transition at about 2 K while it has a quasi-one-dimensional chain structure as well as typical CDW conductors, NbSe$_{3}$, TaS$_{3}$, and NbS$_{3}$. Therefore, TaSe$_{3}$ is one of the suitable materials for the induction of a CDW by doping, and we tried to induce a CDW in TaSe$_{3}$ by doping Cu. Cu concentration was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The high Cu concentration was consistent with the high value of residual resistance ($R(4.5\, \mathrm{K})/(R(280\, \mathrm{K})-R(4.5\, \mathrm{K}))$). Single-crystal X-ray diffraction pattern (XRD) showed an expansion of the $c$-axis in Cu-doped TaSe$_{3}$. The temperature dependence of the resistivity showed the anomaly at 80-100 K in Cu-doped TaSe$_{3}$, which was never observed in pure TaSe$_{3}$. These results suggest that the Cu-doping induces a CDW. We will discuss the relation between the resistivity anomaly and superconductivity.