Bulletin of the American Physical Society
2012 Annual Fall Meeting of the APS Prairie Section
Volume 57, Number 14
Thursday–Saturday, November 8–10, 2012; Lawrence, Kansas
Session A2: Condensed Matter Physics I |
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Chair: Judy Wu, University of Kansas Room: Oread Hotel Griffith Room |
Friday, November 9, 2012 8:30AM - 9:05AM |
A2.00001: Many-body effects in doped graphene sheets Invited Speaker: Giovanni Vignale The peculiar band structure of graphene is responsible for a variety of unusual many-body effects, e.g. a logarithmic divergence of the group velocity of electron quasiparticles near the Dirac point. Interesting many-body effects have also been predicted for doped graphene sheets. Due to the lack of Galilean invariance in this system, both the plasmon frequency and the Drude weight in the optical conductivity are enhanced relative to the standard RPA values. The orbital magnetic susceptibility, which vanishes in the free-electron approximation, is found to be positive, i.e. paramagnetic, and its value is completely controlled by the electron-electron interaction. I review these theoretical predictions vis-a-vis the current state of the experiment. [Preview Abstract] |
Friday, November 9, 2012 9:05AM - 9:17AM |
A2.00002: Third harmonic generation in graphene Nardeep Kumar, Jatinder Kumar, Chris Gerstenkorn, Rui Wang, Hsin-Ying Chiu, Arthur Smirl, Hui Zhao Third-harmonic generation (THG) is a third-order nonlinear optical process. In this process, the electric field of incident light generates a third-order polarization at triple frequency in matter, in addition to the linear and second-order polarizations. Radiation of this polarization gives rise to light at third-harmonic frequency. Here we report the first experimental observations of THG in graphene and few layer graphite. The samples were fabricated by mechanically exfoliating graphene flakes from a bulk graphite crystal with adhesive tapes. The flakes were deposited on Si/SiO$_2$ substrates. The thickness of the flakes was determined by using their optical contrasts and atomic force microscopy measurements. These flakes were irradiate by femtosecond near-infrared laser pulses. The third harmonic generated in these flakes was detected by using a spectrometer. We verified that the wavelength of the emitted light is one third of the incident light, and its intensity increases with the incident light intensity to the third power. We also studied the dependence on the third harmonic generation on the thickness of the flakes. [Preview Abstract] |
Friday, November 9, 2012 9:17AM - 9:29AM |
A2.00003: Heat generation based on graphene with plasmonic nanostructures under illumination Hui-Chun Chien, Guowei Xu, Judy Wu, Hsin-Ying Chiu We study the heat generation based on the graphene decorated with self-assembly silver nanoparticles under uniform illumination. Photoresponse from our devices was observed in high vacuum, which possibly was attributed to the change of interfacial properties between sliver nanoparticles and graphene due to the heat generation by plasmonic-enhanced light trapping. Based on this heat generation mechanism, in this talk, we also present a novel scheme of photodetection with high photoresponsivity by employing liquid electrolyte in our system. Moreover, the photo-thermoelectric device will be proposed for solar energy applications. [Preview Abstract] |
Friday, November 9, 2012 9:29AM - 10:04AM |
A2.00004: High-Performance Lithium-ion Battery Anode Based on Core-Shell Heterostructure of Silicon-Coated Vertically Aligned Carbon Nanofibers Invited Speaker: Jun Li This study reports a high-performance hybrid lithium-ion anode material using coaxially coated Si shells on vertically aligned carbon nanofiber (VACNF) cores. The unique ``cup-stacking'' graphitic microstructure makes VACNFs a good Li$^{+}$ intercalation medium and, more importantly, a robust brush-like conductive core to effectively connect high-capacity Si shells for Li$^{+}$ storage. The vertical core-shell nanowires remain well separated from each other even after coating with bulk quantities of Si (equivalent to over 1.5 $\mu $m thick solid films). This open structure allows the Si shells to freely expand/contract in the radial direction during Li$^{+}$ insertion/extraction. A high specific capacity of 3000-3650 mAh(g$_{Si})^{-1}$, comparable to the maximum value of amorphous Si, has been achieved. About 89{\%} of capacity is retained after 100 charge-discharge cycles at C/1 rate. After long cycling, the electrode material becomes even more stable, showing invariant Li$^{+}$ storage capacity as the charge-discharge rate is increased by 20 times from C/10 to C/0.5 (or 2C). Surprisingly, the measured Li$^{+}$ insertion/extraction capacity increases as the rate is further increased to $\sim $8C. The short diffusion path length for Li$^{+}$ across the thin Si shell is the key to facilitate the fast electrochemical reaction. The ability to obtain high capacity at significantly improved power rates while maintaining the extraordinary cycle stability demonstrates that this novel structure could be a promising anode material for high-performance Li-ion batteries. [Preview Abstract] |
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