Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session A3: Electronic States in Graphene |
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Sponsoring Units: DCMP Chair: Philip Kim, Columbia University Room: Colorado Convention Center Korbel 2A-3A |
Monday, March 5, 2007 8:00AM - 8:36AM |
A3.00001: Infrared Probe of the Anomalous Magneto-transport of Graphite in the Extreme Quantum Limit Invited Speaker: We present a systematic investigation of the magnetoreflectance of highly oriented pyrolytic graphite in magnetic fields $B$ up to 18~T . From these measurements, we report the determination of lifetimes tau associated with the lowest Landau levels in the quantum limit. We find a linear field dependence for inverse lifetime 1$/$tau($B)$ of the lowest Landau levels, which is consistent with the hypothesis of a three-dimensional (3D) to 1D crossover in an anisotropic 3D metal in the quantum limit. This enigmatic result uncovers the origin of the anomalous linear in-plane magnetoresistance observed both in bulk graphite and recently in mesoscopic graphite samples. This work is a collaboration with Z.Q. Li, S.-W. Tsai, W.J. Padilla, S.V. Dordevic, K.S. Burch, and Y.J. Wang. [Preview Abstract] |
Monday, March 5, 2007 8:36AM - 9:12AM |
A3.00002: Two-Dimensional Dirac Fermions in Graphene at High Magnetic Fields Invited Speaker: Graphene, a single atomic sheet of graphite, is a monolayer of carbon atoms densely packed into a honeycomb structure. It can be viewed as either an unrolled single-wall carbon nanotube or a giant flat fullerene molecule. Advances in micromechanical extraction and fabrication techniques for graphite structures now permit such exotic 2D electron systems to be probed experimentally. It has been discovered that the electrons in graphene are two-dimensional Dirac Fermions, based on the observation of half-integer quantum Hall effect and Berry's phase of $\pi $ in the magneto-oscillations. We further investigate the transport properties of graphene in extremely strong magnetic fields. Under such condition, we observe new sets of quantum Hall states at filling factors $\nu =0,\pm 1,\pm 4$, indicating the lifting of the four-fold degeneracy of the previously observed quantum Hall states at $\nu =\pm 4(n+1/2)$, where $n $is the Landau level index. In particular, the presence of the $\nu =0,\pm 1$ quantum Hall states indicates that the Landau level at the charge neutral Dirac point splits into four sub-levels, lifting both sublattice and spin degeneracy in graphene. The quantum Hall effect at $\nu =\pm 1,\pm 4$ is studied in tilted magnetic fields at various temperatures. It has been found that $\nu =\pm 4$ are due to the lifting of the spin-degeneracy of the Landau level $n=\pm 1$ while $\nu =\pm 1$ are most likely due to the sublattice degeneracy lifting of $n=0$. Finally, the availability of large, high quality graphene crystals opens new possibilities for optical and scanning probe studies. A brief discussion of our recent experiments on Raman spectroscopy and STM will be presented. [Preview Abstract] |
Monday, March 5, 2007 9:12AM - 9:48AM |
A3.00003: Electronic Confinement and Coherence in Patterned Epitaxial Graphene Invited Speaker: Transport in ultrathin graphite films grown on single-crystal silicon carbide is dominated by the electron-doped epitaxial graphene layer at the interface and shows graphene characteristics. Epitaxial graphene provides a platform for studying the novel electronic properties of this 2D electron gas in a controlled environment. Shubnikov-de Haas oscillations in the magnetoresistance data indicate an anomalous Berry's phase and reveal the Dirac nature of the charge carriers. The system is highly coherent with phase coherence lengths beyond 1 micrometer at cryogenic temperatures, and mobilities exceeding 2.5 square meters per volt-second. In wide structures, evidence is found for weak anti-localization in agreement with recent graphene weak-localization theory. Patterned narrow ribbons show quantum confinement of electrons. Several Hall bar samples reveal anomalous magnetoresistance patterns consisting of large structured non-periodic oscillations that may be due to a periodic superlattice potential. [Preview Abstract] |
Monday, March 5, 2007 9:48AM - 10:24AM |
A3.00004: First direct observation of Dirac fermions in graphite Invited Speaker: |
Monday, March 5, 2007 10:24AM - 11:00AM |
A3.00005: Electronic properties of single and multi-layer Graphene Invited Speaker: Graphene, a two dimensional carbon crystal with a honeycomb lattice, was discovered only two years ago. It has generated a lot of excitement in the condensed matter community because of its unusual properties: anomalous integer quantum Hall effect, universal d.c. conductivity, absence of weak localization, unusual behavior in high magnetic fields, among others. In this talk I am going to discuss the various non-Fermi liquid properties of single layer, bilayer, and multi-layer graphene. These results indicate that graphene belongs to a new class of materials with unique properties that can be used as basis for a carbon based electronics. [Preview Abstract] |
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