Anisotropic multichain nature and filamentary superconductivity in the charge density wave system HfTe3

Abstract

Single crystals of ${\mathrm{HfTe}}_{3}$ were successfully grown using a chemical transport reaction in an extremely narrow temperature range. Here, we report a comparative study of polycrystalline and single-crystal samples. The electrical resistivity $\ensuremath{\rho}(T)$ measured on polycrystalline samples shows a broad hump and clear drop at 80 and 1.7 K, which correspond to the formation of the charge density wave (CDW) and superconducting (SC) transition, respectively. For the single crystals, $\ensuremath{\rho}(T)$ shows a sharp change at ${T}_{\mathrm{CDW}}=93$ K, and the superconductivity is absent, in contrast to the polycrystalline samples. With the current flowing along the $a$ and $b$ directions, the coincidence of the linear temperature dependence of $\ensuremath{\rho}(T)/\ensuremath{\rho}(300\phantom{\rule{4pt}{0ex}}\mathrm{K})$ above ${T}_{\mathrm{CDW}}$ strongly implies that the electron-electron scattering mechanism dominates the transport properties in a quasi-one-dimensional chain. Furthermore, a metal-semiconductor-like transition is confirmed below ${T}_{\mathrm{CDW}}$ in ${\ensuremath{\rho}}_{c}$. The drop observed at 4.3 K in ${\ensuremath{\rho}}_{b}(T)$ for the single crystal with more defects (small residual resistivity ratio, large ${\ensuremath{\rho}}_{0}$, and weak drop) provides direct evidence of a disorder-related SC fluctuation in the CDW system. With temperature decreasing, the carrier density exhibits a similar and rapid decrease below ${T}_{\mathrm{CDW}}$ for flowing current in both the $a$ and $b$ directions, whereas an obvious enhancement of carrier mobility appears as $I\ensuremath{\parallel}b$. An analysis of x-ray photoelectron spectroscopy spectra suggests that the mixed-valence states of Hf and Te could be related to the CDW formation in the multichain system of ${\mathrm{HfTe}}_{3}$.