Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session D1: Goeppert Mayer Award, IUPAP Young Scientist Award, and Apker Award Session |
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Sponsoring Units: DCMP Chair: Samuel Bader, Argonne National Laboratory Room: Oregon Ballroom 201 |
Monday, March 15, 2010 2:30PM - 3:06PM |
D1.00001: Maria Goeppert Mayer Award Talk: Dirac fermions in epitaxial and free standing graphene Invited Speaker: In this talk I will present a summary of our experimental work in the emerging field of graphene 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 and discuss how many body interactions evolve from free standing to epitaxial graphene and how engineering of small terraces size down to nm size can strongly affect the properties of Dirac fermions. The implications of our study on the properties of Dirac materials and their potential role for applications are discussed. [Preview Abstract] |
Monday, March 15, 2010 3:06PM - 3:42PM |
D1.00002: IUPAP Young Scientist Award Talk: Bilayer graphene: tunable bandgap and electron-phonon Fano resonances Invited Speaker: Graphene, a single layer of carbon atoms, exhibits novel two-dimensional electronic behavior. With an extra layer, bilayer graphene gives rise to even richer behavior. In this talk, I will describe how we can use electrical gating to control the electronic bandgap in bilayer graphene and probe the induced bandgap using infrared spectroscopy. I will also discuss a new elementary excitation composed of coupled phonon and exciton unique in this tunable bandgap semiconductor. This hybrid phonon-exciton excitation shows striking Fano interference behavior. [Preview Abstract] |
Monday, March 15, 2010 3:42PM - 4:18PM |
D1.00003: LeRoy Apker Award Talk: High Resolution Thermoreflectance Imaging of Thermal Coupling in Vertical Cavity Surface Emitting Laser Arrays Invited Speaker: Vertical cavity surface emitting laser (VCSEL) arrays have received increased attention over the past several years for use in telecommunications as high speed parallel data transmission devices, optical interconnects, and data storage devices. The increased packing density of the VCSELs in arrays has lead to undesirable thermal effects such as inter-element thermal crosstalk between individual lasers. Previous work has used a variety of techniques to measure the temperature of VCSELs; however, these techniques are usually single-point average measurements that lack sufficient spatial and thermal resolution. Instead, we present work utilizing high spatial (250nm) and thermal (10mK) resolution thermoreflectance microscopy to obtain two dimensional images of the surface temperature of VCSEL arrays. These temperature measurements show significant thermal coupling between VCSELs in the array, thermal lensing in the lasing VCSEL, and temperature gradients across adjacent lasers. In addition, thermoreflectance microscopy measurements reveal an offset between the optical mode and the hotspot for VCSELs in the array. The thermoreflectance results are used to calculate the radial thermal conductivity of the VCSEL array. A comparison of the thermoreflectance results to traditional wavelength shift measurements of the VCSEL temperature reveals an offset between the two techniques. We attribute this offset to the wavelength shift technique measuring the average cavity temperature of the VCSELs while thermoreflectance microscopy measures the surface temperature. Lastly, to better understand the speed of heat diffusion in the array, we use a time resolved temperature measurement technique to measure the thermal diffusivity of the complex VCSEL array structure. The thermal diffusivity value calculated is in good agreement with prior results on bulk and thin film structures of the same material. [Preview Abstract] |
Monday, March 15, 2010 4:18PM - 4:54PM |
D1.00004: LeRoy Apker Award Talk: Small-Model Approximations to Ising Models of Two-Dimensional Geometrically Frustrated Systems Invited Speaker: In geometrically frustrated spin systems, it is impossible for all local spin-spin interactions to be at their respective ground states simultaneously. These systems have many interesting properties. Most notably, they have many energy ground states and their entropy does not vanish at zero Kelvin, violating the third law of thermodynamics. Currently, there are two primary methods for studying the thermodynamic properties of frustrated systems: the exact analytical method and the Monte Carlo simulation. However, the exact analytical method is difficult and not always possible, while the Monte Carlo simulation can often be very time-consuming. In view of this, we have investigated small systems with less than 30 spins to approximate the energy and the specific heat of three extended 2D lattices, including the triangular lattice, the Kagome lattice and the triangular Kagome lattice, and found that the small systems can be good approximations to the extended lattices if they satisfy a set of criteria. This method of using small systems as approximations may provide us an efficient way to do a first approximation of the properties of frustrated systems. [Preview Abstract] |
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