Events at Physics |
Events on Tuesday, October 20th, 2009
- R. G. Herb Condensed Matter Seminar
- Delocalization by disorder: non-metallic transport in layered metals
- Time: 10:00 am
- Place: 5310 Chamberlin
- Speaker: Dmitrii Maslov, University of Florida
- Abstract: Electron transport in many layered metals exhibits a number of puzzling anomalies: for example, while the temperature dependence of the in-plane resistivity is metallic, that of the out-of-plane resistivity is insulating or even non-monotonic. Also, it is often the case that the resistivity anisotropy cannot be accounted simply by mass anisotropy, which implies that disorder is strongly anisotropic as well. We show that, contrary to the widely accepted paradigm of "coherent-incoherent crossover", the Boltzmann equation is applicable to layered systems both for elastic and Eliashberg-type (dynamic) inelastic scattering as long as the "good-metal" condition (E_Fτ) is satisfied and disorder is not correlated. Therefore, a model containing only those sources of scattering cannot explain the experiment. We propose a model of two-channel transport, in which electrons propagate across the layers in two ways--coherently and via phonon-assisted tunneling through random resonant centers--and show how the experiment can be explained within this model. We also propose an explanation of anomalously large resistivity anisotropy in a model of two types of disorder: planar defects and isotropic impurities. We solve this model by mapping it onto the exact Berezinskii's solution of 1D localization problem and show that isotropic impurities destroy localization induced by planar defects.
- Host: Andrey Chubukov
- Chaos & Complex Systems Seminar
- High-Energy neutrino astronomy: Towards a kilometer-scale neutrino observatory.
- Time: 12:05 pm
- Place: 4274 Chamberlin (Refreshments will be served)
- Speaker: Francis Halzen, UW Department of Physics
- Abstract: Kilometer-scale neutrino detectors such as IceCube are discovery instruments covering nuclear and particle physics, cosmology and astronomy. Examples of their multidisciplinary missions include the search for the particle nature of dark matter and for additional small dimensions of space. In the end, their conceptual design is very much anchored to the observational fact that Nature produces photons and protons with energies in excess of one hundred and one hundred million Terraelectronvolts, respectively. The cosmic ray connection sets the scale of cosmic neutrino fluxes. The problem has been to develop a robust and affordable technology to build the kilometer-scale neutrino detectors required to detect candidate sources such as supernova remnants and active galxies. The AMANDA telescope transforming ultra-clear deep Antarctic ice into a Cherenkov detector of muons and showers initiated by neutrinos of all three flavors, has met this challenge. Having collected more than 6000 well-reconstructed muon neutrinos of 50 GeV ~ 500 TeV energy, AMANDA represented a proof of concept for the ultimate kilometer-scale neutrino observatory, IceCube, now almost complete and producing results exceeding seven years of AMANDA data in sensitivity.