| AVS 60th International Symposium and Exhibition | |
| Graphene and Other 2D Materials Focus Topic | Wednesday Sessions |
| Session GR+AS+EM+NS+SS-WeA |
| Session: | Dopants, Defects and Interfaces in 2D Materials |
| Presenter: | T. Kondo, University of Tsukuba, Japan |
| Authors: | T. Kondo, University of Tsukuba, Japan D. Guo, University of Tsukuba, Japan T. Sikano, University of Tsukuba, Japan T. Suzuki, University of Tsukuba, Japan M. Sakurai, University of Tsukuba, Japan J. Nakamura, University of Tsukuba, Japan |
| Correspondent: | Click to Email |
The charge carriers in graphene are known to follow a relativistic Dirac equation and behave as massless Dirac fermions [1]. In a magnetic field, massless Dirac fermions in graphene exhibit a relativistic Landau-level quantization and an anomalous quantum Hall effect [2,3]. The Landau-level energy sequence in graphene (single layer) shows a square-root dependence on both the magnetic field and the Landau index n, where a zeroth Landau level appears at the Dirac point. However, we have recently reported based on the scanning tunneling spectroscopy (STS) that the Landau levels of massless Dirac fermions generate in the absence of an external magnetic field on a partially potassium-intercalated highly oriented pyrolytic graphite (K-HOPG) surface [4]. The observation of the Landau levels of massless Dirac fermions indicates appearance of the graphene characters in K-HOPG. The generation of the Landau levels is ascribed to a vector potential induced by the perturbation of nearest-neighbour hopping, which may originate from a strain or a gradient of on-site potentials at the perimeters of potassium-free domains. There are other reports that the strain of graphene induces the Landau levels generation under the zero magnetic fields [5-8]. Here, we report the generation of the Landau levels of massive Dirac fermions on a nitrogen-doped graphite (N-HOPG) surface without strain under the zero magnetic fields. The pseudomagnetic fields are estimated to be as much as 60 T. Landau levels are observed at the flat area of the N-HOPG surface and thus the strain can be excluded as the possible origin of the perturbation of nearest-neighbour hopping. According to XPS, STM, and STS, our N-HOPG sample was found to consist mainly of the graphitic-N species which has a positive charge and modulates a potential on the surface [9]. Therefore, the generation of the Landau levels on N-HOPG is probably originated from a gradient of on-site potentials of carbon across the domain of the equipotential contour induced by the dopant graphitic-N species of N-HOPG.
[2] K.S.Novoselov, et al. Nature 438, 197 (2005).
[3] Y. Zhang, et al., Nature 438, 201 (2005).
[4] D.Guo, T.Kondo, J.Nakamura et al., Nature Communications 3, 1068 (2012).
[5] N.Levy, et al. Science 329, 544 (2010).
[6] H.Yan, et al., Phys. Rev. B 85, 035422 (2012).
[7] K.K.Gomes, et al., Nature, 483, 306 (2012).
[8] J. Lu, A.H. C. Neto and K.P.Loh, Nature Communications 3, 823 (2012).
[9] T.Kondo, S.Casolo, J.Nakamura, et al., Phys. Rev. B 86, 035436 (2012).