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Events on Monday, October 3rd, 2011

Plasma Physics (Physics/ECE/NE 922) Seminar
Time: 12:05 pm
Place: 2317 Engineering Hall
Speaker: Greg Howes, University of Iowa
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R. G. Herb Condensed Matter Seminar
Fe-based superconductors at high magnetic fields
Time: 1:30 pm
Place: 5310 Chamberlin
Speaker: Alex Gurevich, Old Dominion University
Abstract: Low carrier densities and short coherence lengths in the recently discovered semi-metallic Fe-based superconductors (FBS) can result in exotic behaviors at strong magnetic fields due to the interplay of multiband superconductivity, unconventional pairing symmetry and the Zeeman and orbital pairbreaking. I this talk I will give an overview of these effects, particularly the anomalous temperature dependencies of the upper critical field Hc2(T) which often extrapolate to Hc2 > 100 Tesla at low temperatures for some FBS. The materials features of FBS and the multiband s+/- pairing symmetry with the sign change of the order parameter on different sheets of the Fermi surface can significantly increase Hc2(T) and facilitate the Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) transition to the state with a spatially modulated order parameter. Small shifts of the chemical potential upon doping of FBS can produce new small pockets of the Fermi surface, triggering the FFLO instability due to the Lifshitz transition. I will also discuss the effect of disorder, particularly magnetic defects produced by α-particle irradiation.
Host: Rzchowski
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Condensed Matter Theory Group Seminar
Strong coupling theory of quantum critical points in heavy fermion compounds
Time: 4:30 pm
Place: 5310 Chamberlin
Speaker: Peter Wölfle, Karlsruhe Institute of Technology, Germany
Abstract: Following a brief general introduction into quantum phase transitions the case of antiferromagnetic transitions in heavy fermion metals is discussed. It is shown that in certain cases the effective mass of fermionic quasiparticles diverges at the critical point. Using an extension of Landau quasiparticle theory the coupling of the critical behavior in the fermionic and bosonic sector is shown to lead to a new type of scaling behavior with unusual critical exponents. The theory accounts well for the up to now unexplained critical behavior of YbRh2Si2.
Host: Perkins
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