Magnetic field-driven superconductor-insulator transition in boron-doped nanocrystalline chemical vapor deposition diamond

The systematics of the suppression of superconductivity with increasing magnetic field in boron-doped nanocrystalline chemical vapor deposition diamond is studied in a broad temperature range. At the temperature of T(S0) which is above the critical temperature, a plateau is observed in the resistivity versus temperature curve rho(T) taken at zero magnetic field. When a magnetic field of B=B(SN) (N=1,2, ... ,5) is applied, the plateau moves to low temperature with the thermoresistivity maximum located at T(SN) (N=1,2, ... ,5). The rho(B) curves, measured at different temperatures around T(SN), intersect in the rho-B plane at the field of B=B(SN). By tuning B(SN) from 0 to 5 T, a series of plateaus in the rho-T plane and the corresponding intersections in the rho-B plane are observed. The intersections quadratically chain up in the rho-B plane, separating the superconducting from the insulating region. The thermoresistivity maxima exponentially group up in the rho-T plane, thus defining a phase fluctuation zone. The phase boundary, composed of the intersections and separating the superconducting states from the insulating state, is shown to be a generic consequence of granularity. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3437653]