Metal-insulator transition and superconductivity in boron-doped diamond

• Published in: Physical review. B, Condensed matter and materials physics Vol. 75; no. 16; p. 165313
• Main Authors: Klein, T., Achatz, P., Kacmarcik, J., Marcenat, C., Gustafsson, F., Marcus, J., Bustarret, E., Pernot, J., Omnes, F., Sernelius, Bo E., Persson, C., Ferreira da Silva, A., Cytermann, C.
• Format: Journal Article
• Language: English
• Published: American Physical Society 17-04-2007
• Subjects: boron; Condensed Matter; diamond; electron-phonon interactions; Fysik; Hall effect; hopping conduction; metal-insulator transition; NATURAL SCIENCES; NATURVETENSKAP; Physics; superconducting materials; superconducting thin films; superconducting transition temperature; superconducting transitions; Superconductivity; superconductivity; diamond; metal-insulator transition
• ISSN: 1098-0121; 1550-235X; 1550-235X
• DOI: 10.1103/PhysRevB.75.165313

We report on a detailed analysis of the transport properties and superconducting critical temperatures of boron-doped diamond films grown along the $\{100\}$ direction. The system presents a metal-insulator transition (MIT) for a boron concentration ($n_B$) on the order of $n_c \sim 4.5 \times 10^{20}$ cm$^{-3}$ in excellent agreement with numerical calculations. The temperature dependence of the conductivity and Hall effect can be well described by variable range hopping for $n_B n_c$) present a superconducting transition at low temperature. The zero temperature conductivity $\sigma_0$ deduced from fits to the data above the critical temperature ($T_c$) using a classical quantum interference formula scales as : $\sigma_0 \propto (n_B/n_c-1)^\nu$ with $\nu \sim 1$. Large $T_c$ values ($\geq 0.4$ K) have been obtained for boron concentration down to $n_B/n_c \sim 1.1$ and $T_c$ surprisingly mimics a $(n_B/n_c-1)^{1/2}$ law. Those high $T_c$ values can be explained by a slow decrease of the electron-phonon coupling parameter $\lambda$ and a corresponding drop of the Coulomb pseudo-potential $\mu^*$ as $n_B \rightarrow n_c$.