STM/STS measurements of quasi two-dimensional electronic states near artificially created defects in magnetic fields

We observed the local density of states (LDOS) of a quasi two-dimensional electron system near defects, artificially created by Ar-ion sputtering, on a surface of highly oriented pyrolytic graphite in magnetic fields with ultra-low temperature scanning tunneling spectroscopy. In differential tunnel conductance images taken at the valley energies in between the adjacent Landau levels, two typical localized distributions of the LDOS were observed depending on the defects. We reveal that the defect potential depth is responsible for the two types of the spatial distributions of LDOS.