Abstract
Under perpendicular external magnetic fields, two-dimensional carriers exhibit Landau levels (LLs). However, it has recently been reported that LLs have been observed on graphene and graphite surfaces without external magnetic fields being applied. These anomalous LLs have been ascribed primarily to a strain of graphene sheets, leading to in-plane hopping modulation of electrons. Here, we report the observation of the LLs of massive Dirac fermions on atomically flat areas of a nitrogen-doped graphite surface in the absence of external magnetic fields. The corresponding magnetic fields were estimated to be as much as approximately 100 T. The generation of the LLs at the area with negligible strain can be explained by inequivalent hopping of π electrons that takes place at the perimeter of high-potential domains surrounded by positively charged substituted graphitic-nitrogen atoms.
Highlights
Under perpendicular external magnetic fields, two-dimensional carriers exhibit Landau levels (LLs)
The nitrogen-doped graphite used in this study was prepared by nitrogen ion bombardment of an highly oriented pyrolytic graphite (HOPG) surface at room temperature, followed by annealing at 900 K in an ultra high-vacuum chamber
As the line profile along the atomic arrangement shows, the observed surface region (Fig. 1e) is atomically flat, i.e., there is no apparent corrugation, while there is a sinusoidal curve with the periodicity of β -site carbon of Bernal-stacked graphite, 0.245 ± 0.01 nm, which is typically observed at the flat region of the pristine graphite surface by STM16
Summary
Under perpendicular external magnetic fields, two-dimensional carriers exhibit Landau levels (LLs). It has recently been reported that LLs have been observed on graphene and graphite surfaces without external magnetic fields being applied. These anomalous LLs have been ascribed primarily to a strain of graphene sheets, leading to in-plane hopping modulation of electrons. We report the observation of the LLs of massive Dirac fermions on atomically flat areas of a nitrogendoped graphite surface in the absence of external magnetic fields. In the presence of an external magnetic field, charge carriers of conductive material circulate in cyclotron orbits perpendicular to the field, with quantised energies called Landau levels (LLs). The LLs energies are described as follows[1,5,6,7]: En
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