Metal-insulator transition and anomalous lattice parameters changes in Ru-doped VO2

Abstract

${\mathrm{VO}}_{2}$, of interest for decades due to both its phenomenology and its potential applications, has a monoclinic distortion of the rutile crystal structure at ambient temperature that is coupled to its metal-insulator transition. In contrast, ${\mathrm{RuO}}_{2}$ has three electrons more per formula unit, is a metallic conductor, and has an undistorted rutile structure. Here, we report a systematic study of Ru-doped ${\mathrm{VO}}_{2}$ (${\mathrm{V}}_{1\text{\ensuremath{-}}x}{\mathrm{Ru}}_{x}{\mathrm{O}}_{2}, 0.01\ensuremath{\le}x\ensuremath{\le}0.9)$, generally characterizing its crystal structure, magnetic and electronic properties, and heat capacity. The composition-dependent Wilson ratio is determined. We find that an unusually high Ru doping value (80%, $x=0.8$) is required to achieve a metallic state in ${\mathrm{V}}_{1\text{\ensuremath{-}}x}{\mathrm{Ru}}_{x}{\mathrm{O}}_{2}$. No superconductivity was observed down to 0.1 K in the metallic materials. We propose a possible understanding for how the insulating state can exist in ${\mathrm{V}}_{1\text{\ensuremath{-}}x}{\mathrm{Ru}}_{x}{\mathrm{O}}_{2}$ at high Ru contents.