Finger patterns of magnetic flux in bulk Bi2Sr2CaCu2O8+delta samples

Fingerlike flux patterns, normally observed in superconducting films, are demonstrated in a bulk material. We observed such patterns in Bi2Sr2CaCu2O8+delta crystals with an artificial barrier separating regions of different magnetic diffusivity, created by irradiating one-half of the crystal with heavy ions. Flux penetration from the nonirradiated part of the crystal, through the barrier, into the irradiated part forms fingerlike patterns in a wide range of temperatures and field ramping rates. The mechanism responsible for the observed patterns is discussed.