Electrical anisotropy and coexistence of structural transitions and superconductivity in IrTe2

Abstract

We report experimental investigations of the electrical transport, magnetic, and thermodynamic properties of $\mathrm{IrT}{\mathrm{e}}_{2}$ single crystals. The resistivity, magnetization, and specific heat display anomalies at ${T}_{\mathrm{S}1}\ensuremath{\approx}283\phantom{\rule{0.16em}{0ex}}\mathrm{K},{T}_{\mathrm{S}2}\ensuremath{\approx}167\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, and ${T}_{\mathrm{c}}\ensuremath{\approx}2.5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, corresponding to two structural and one superconducting phase transitions, respectively, demonstrating the coexistence of all of these transitions in high-quality stoichiometric samples. While there is little magnetic anisotropy, a large $ab$-plane $({\ensuremath{\rho}}_{\mathrm{ab}})$ and $c$-axis $({\ensuremath{\rho}}_{\mathrm{c}})$ electrical resistivity ratio $({\ensuremath{\rho}}_{\mathrm{c}}/{\ensuremath{\rho}}_{\mathrm{ab}}\ensuremath{\approx}730$ at $T=4\phantom{\rule{0.16em}{0ex}}\mathrm{K})$ is observed. This two-dimensional (2D) electronic character is further reflected in the disparate temperature dependences of ${\ensuremath{\rho}}_{\mathrm{ab}}$ and ${\ensuremath{\rho}}_{\mathrm{c}}$, with ${\ensuremath{\rho}}_{\mathrm{ab}}$ exhibiting a Fermi-liquid-like ${T}^{2}$ dependence below $\ensuremath{\sim}25\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, while ${\ensuremath{\rho}}_{\mathrm{c}}$ deviates significantly from this standard metallic behavior. In contrast, the magnetization is almost isotropic and negative over a wide temperature range. This can be explained by larger diamagnetism induced by electronic structure reconstruction as probed by the Hall effect and smaller positive contribution from itinerant electrons due to a low density of states (DOS) at the Fermi level. A small electronic specific heat coefficient with $\ensuremath{\gamma}\ensuremath{\approx}\phantom{\rule{0.16em}{0ex}}1.8\phantom{\rule{0.16em}{0ex}}\mathrm{mJ}/\mathrm{mol}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{2}$ confirms this assertion. This implies that $\mathrm{IrT}{\mathrm{e}}_{2}$ is a weakly coupled superconductor. The connection between the superconductivity and the two structural transitions is discussed.