Superconductivity in polycrystalline boron-doped diamond synthesized at 20GPa and 2700K

Bulk sample (∼7.5mm3) of boron-doped diamond containing 2.6(0.6)at.%B was synthesized by means of direct reaction between boron carbide and graphite in multianvil apparatus at 20GPa and 2700K. Electrical resistance of the sample of B-doped polycrystalline diamond was measured in the temperature interval from 10mK to 300K and revealed a transition to superconducting state at 2.4–1.4K. Our results imply that increase of synthesis pressure from 8–9GPa [Ekimov et al., Nature 428, 542 (2004)] to 20GPa does not significantly affect boron content in diamond but decreases the temperature of the transition to superconducting state. We observed sharpening of the temperature interval of the transition to superconducting state in magnetic field that may suggest that superconductivity in our samples could arise from filaments of zero-resistant material.