| AVS 59th Annual International Symposium and Exhibition | |
| Graphene and Related Materials Focus Topic | Monday Sessions |
| Session GR+EM+ET+NS+TF-MoA |
| Session: | Electronic Properties and Charge Transport |
| Presenter: | J. Chae, Center for Nanoscale Science and Technology / NIST |
| Authors: | J. Chae, Center for Nanoscale Science and Technology / NIST S. Jung, Center for Nanoscale Science and Technology / NIST Y. Zhao, Center for Nanoscale Science and Technology / NIST N.B. Zhitenev, Center for Nanoscale Science and Technology / NIST J.A. Stroscio, Center for Nanoscale Science and Technology / NIST A. Young, Columbia University C. Dean, Columbia University L. Wang, Columbia University Y. Gao, Columbia University J.C. Hone, Columbia University K.L. Shepard, Columbia University P. Kim, Columbia University |
| Correspondent: | Click to Email |
The single-particle spectrum of graphene is described by massless Dirac quasiparticles with a linear energy-momentum dispersion relation. In this talk I examine the effect of electron interactions on the graphene energy dispersion as a function of both excitation energy E away from the Fermi energy and density n. To analyze the dispersion, we measure the Landau levels (LLs) in graphene on a hexagonal boron nitride (hBN) insulator in low magnetic fields by scanning tunneling spectroscopy. The experiments were performed in a custom designed cryogenic scanning tunneling microscope system operating at 4 K with applied magnetic fields from 0 T to 8 T. The graphene devices were fabricated by the method detailed in Dean et al. [1]. The disorder in graphene on hBN is reduced in comparison with the previous measurements in graphene on SiO2 [2] allowing us to observe the LLs in fields as low as 0.5 T. By fitting the LL energies obtained at constant density, we find that the energy dispersion remains linear, characterized by a momentum-independent renormalized velocity. However, the renormalized velocity is density dependent, showing a strong increase as the charge neutrality point is approached. The overall spectrum renormalization can be described as a squeezing of the Dirac cone angle due to electron-electron interactions at low densities. Interestingly, we also find that the renormalization of the dispersion velocity is affected by the local disorder potential and magnetic field, which is not described by current theory.
[1]. C. Dean, A. Young, I. Meric, C. Lee, L. Wang, S. Sorgenfrei, K. Watanabe, T. Taniguchi, P. Kim, K. L. Shepard, and J. Hone, Nature Nanotech. 5, 722–726 (2010).
[2]. S. Jung, G. M. Rutter, N. N. Klimov, D. B. Newell, I. Calizo, A. R. Hight-Walker, N. B. Zhitenev, and J. A. Stroscio, Nature Phys. 7, 245–251 (2011).