Low-temperature transport in highly boron-doped nanocrystalline diamond

• Published in: Physical review. B, Condensed matter and materials physics Vol. 79; no. 20
• Main Authors: Achatz, P., Gajewski, W., Bustarret, E., Marcenat, C., Piquerel, R., Chapelier, C., Dubouchet, T., Williams, O. A., Haenen, K., Garrido, J. A., Stutzmann, M.
• Format: Journal Article
• Language: English
• Published: American Physical Society 01-05-2009
• Subjects: Condensed Matter; Disordered Systems and Neural Networks; Physics; Superconductivity
• ISSN: 1098-0121; 1550-235X
• DOI: 10.1103/PhysRevB.79.201203

We studied the transport properties of highly boron-doped nanocrystalline diamond thin films at temperatures down to 50 mK. The system undergoes a doping-induced metal-insulator transition with an interplay between intergranular conductance g and intragranular conductance g0, as expected for a granular system. The conduction mechanism in the case of the low-conductivity films close to the metal-insulator transition has a temperature dependence similar to Efros-Shklovskii type of hopping. On the metallic side of the transition, in the normal state, a logarithmic temperature dependence of the conductivity is observed, as expected for a metallic granular system. Metallic samples far away from the transition show similarities to heavily borondoped single-crystal diamond. Close to the transition, the behavior is richer. Global phase coherence leads in both cases to superconductivity also checked by ac susceptibility , but a peak in the low-temperature magnetoresistance measurements occurs for samples close to the transition. Corrections to the conductance according to superconducting fluctuations account for this negative magnetoresistance.