Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session A1: Graphene - Spectroscopies |
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Sponsoring Units: DCMP Chair: Amir Yacoby, Harvard University. Room: Spirit of Pittsburgh Ballroom A |
Monday, March 16, 2009 8:00AM - 8:36AM |
A1.00001: Infrared spectroscopy of gated structures based on single- and bi-layer graphene Invited Speaker: Infrared spectroscopy was employed to investigated the charge dynamics in graphene integrated in tunable gated devices (Nature Physics 4, 532 (2008)). These measurements verified that electrons in single-layer graphene behave like Dirac quasiparticles but most importantly revealed several unexpected results that are beyond the theoretical predictions for idealized graphene. Several of our findings including, a systematic enhancement of the Fermi velocity at low energy and also the ``residual'' conductivity at frequencies below 2E$_F$ are indicative of many-body interactions. Recent infrared study of bilayer graphene uncovered a pronounced asymmetry in the optical conductivity upon injection of electrons and holes (arXiv:0807.3776). We believe this result is suggestive of a marked asymmetry between the valence and conduction bands in bilayer samples. [Preview Abstract] |
Monday, March 16, 2009 8:36AM - 9:12AM |
A1.00002: Scanning tunneling microscopy and spectroscopy of graphene on graphite Invited Speaker: Graphene, a single atomic layer of crystalline carbon, exhibits fascinating electronic properties owing to low energy quasiparticles that resemble relativistic Dirac fermions. Recent experiments on graphene deposited on insulating substrates revealed that substrate induced potential fluctuations obscure the Dirac fermion nature of the carriers. Using low temperature scanning tunneling microscopy (STM) and spectroscopy (STS) we demonstrated that substrate induced potential fluctuations are substantially reduced when graphene is deposited on graphite and that in these samples the intrinsic structural and electronic properties of graphene become accessible. We observed the honeycomb structure and the V shaped density of states that vanishes at the Dirac point, characteristic of Dirac fermions. In finite magnetic field we observed the appearance of a single sequence of Landau levels, with square root dependence on level index and field, further attesting to the Dirac fermion nature of the charge carriers. The experiments give access to the fundamental parameters of the electronic spectrum in graphene including the Fermi velocity, electron-phonon coupling constant and electron-electron interactions. In addition they revealed the appearance of a small gap at the Dirac point and an anomaly at the Fermi energy. Work in collaboration with E.Y. Andrei and A. Luican. \\[4pt] [1] G. Li and E.Y. Andrei, Nature Phys. 3, 623 (2007). \\[0pt] [2] G. Li, A. Luican, and E.Y. Andrei, http://arxiv.org/abs/0803.4016 [Preview Abstract] |
Monday, March 16, 2009 9:12AM - 9:48AM |
A1.00003: Tuning the properties of Dirac fermions in graphene Invited Speaker: Graphene, a one atom thick layer of carbon, the supposedly ideal Dirac material, has been under the radar of theorists and experimentalist for many decades. Although novel physical properties were envisioned, graphene, as any other 2D material, was presumed not to exist in its free state because of long wavelength fluctuations will easily destroy purely 2D membranes. The recent success in isolating a single sheet of graphene has certainly challenged this view. In this talk I will present our experimental work in this field using a combination of spectroscopic and microscopy tools. I'll present experimental evidence of what drives the stability of a graphene membrane and show comparison between exfoliated and epitaxial graphene. I will then discuss the nature of fermions in graphene sheets and how their peculiar electronic structure can be tuned by engineering small terraces of graphene down to nm size, where the physics gets dominated by quantum confinement. The implications of our study on the properties of Dirac materials and their potential role for applications are discussed. [Preview Abstract] |
Monday, March 16, 2009 9:48AM - 10:24AM |
A1.00004: The infrared conductivity of graphene Invited Speaker: The discovery of graphene is probably one of the most important events in modern condensed matter physics. Besides being a material that is only one atom thick, it has electronic properties which are usual when compared with ordinary metals and semiconductors. These unusual properties are reflected in its infrared conductivity. We will discuss the physical processes that affect the low frequency conductivity of graphene. We show that while the standard model of graphene is capable of explaing most of the features, it also fails in some aspects, indicating that we still do not have a full understanding of the physical mechanisms that control the electronic properties of this amazing material. [Preview Abstract] |
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