Abstract
We measured the local density of states of a quasi two-dimensional electron system (2DES) near defects, artificially created by Ar-ion sputtering, on surfaces of highly oriented pyrolytic graphite (HOPG) with scanning tunneling spectroscopy (STS) in high magnetic fields. At valley energies of the Landau level spectrum, we found two typical localized distributions of the 2DES depending on the defects. These are new types of distributions which are not observed in the previous STS work at the HOPG surface near a point defect [Y. Niimi, Phys. Rev. Lett. 97, 236804 (2006).10.1103/PhysRevLett.97.236804]. With increasing energy, we observed gradual transformation from the localized distributions to the extended ones as expected for the integer quantum Hall state. We show that the defect potential depth is responsible for the two localized distributions from comparison with theoretical calculations.
Highlights
We measured the local density of states of a quasi two-dimensional electron system (2DES) near defects, artificially created by Ar-ion sputtering, on surfaces of highly oriented pyrolytic graphite (HOPG) with scanning tunneling spectroscopy (STS) in high magnetic fields
These are powerful techniques to investigate the local density of states (LDOS) at sample surfaces
More distinct localization and extension of the LDOS depending on energy, which indicate the possible quantum Hall (QH) state, have been observed near a point defect at surfaces of highly oriented pyrolytic graphite (HOPG) [7]
Summary
We measured the local density of states of a quasi two-dimensional electron system (2DES) near defects, artificially created by Ar-ion sputtering, on surfaces of highly oriented pyrolytic graphite (HOPG) with scanning tunneling spectroscopy (STS) in high magnetic fields. More distinct localization and extension of the LDOS depending on energy, which indicate the possible QH state, have been observed near a point defect at surfaces of highly oriented pyrolytic graphite (HOPG) [7]. At the valley energy in between LL0; À1 and LL1 [Fig. 2(a)], the electronic states are strongly or weakly localized near some of the defects.
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