Aharonov-Bohm effect on columnar defects in thin graphite and graphene

We studied Aharonov-Bohm effect on thin graphite single crystals containing columnar defects (nanoholes) produced by irradiation with heavy ions. The thickness of irradiated single crystals has been varied from 50 nm down to less then 1 nm by thinning the thicker samples with beam-plasma etching. For irradiated samples we found the existence of oscillating, field-periodic contribution of magnetoresistance with a periodicity corresponding to the flux quantum hc/e per area of nanohole independently of sample thickness. The results point to the significant contribution of Dirac fermions to the oscillating part of magnetoresistance and also to the existence of the edge states located near the nanohole perimeter.