  Superconducting transport properties of granular materials are greatly
influenced by the microstructure. We show that in heavily boron-doped diamond
films (HBDDF) films some sharp transport features can be manipulated by
applying a magnetic field and controlled finite bias current. We demonstrate
the conductivity cross-over from dirty metal to the superconducting state
through an insulating peak arising at a very low current or magnetic field
region and particularly pronounced negative magnetoresistance with periodic
oscillatory features. The current-voltage characteristics show features of the
Berezinskii-Kosterlitz-Thouless (BKT) phase transitions which verifies the
two-dimensional structure in HBDDF observed recently. A zero bias conductance
peak can be attributed to the Andreev bound state formed at the grain
boundaries of diamond nanocrystals. The set of observations can be
qualitatively explained consistently through the concept of a superconducting
transition with a non-s wave order parameter in the diamond heterostructures.
