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VERSION:2.0
CALSCALE:GREGORIAN
PRODID:UW-Madison-Physics-Events
BEGIN:VEVENT
SEQUENCE:0
UID:UW-Physics-Event-2997
DTSTART:20130401T213000Z
DURATION:PT1H0M0S
DTSTAMP:20260420T020345Z
LAST-MODIFIED:20130329T160756Z
LOCATION:5310 Chamberlin
SUMMARY:Manifestations of electronic nematic degrees of freedom in the
  high-temperature iron-based superconductors\, Condensed Matter Theory
  Group Seminar\, Rafael Fernandes\, University of Minnesota
DESCRIPTION:Five years after their discovery\, much of the interest in
  iron-pnictide materials remains in understanding not only their super
 conducting transition at nearly 60K\, but also the nature of their nor
 mal state. In this context\, a hotly debated topic is the origin of th
 e tetragonal to orthorhombic transition\, which either precedes or hap
 pens simultaneously to a magnetic instability\, and persists even in t
 he vicinities of the superconducting dome. Experiments have revealed t
 hat the anisotropies in this orthorhombic phase cannot be explained by
  the small lattice distortion alone\, suggesting that the tetragonal s
 ymmetry breaking is driven by electronic degrees of freedom\, dubbed n
 ematic in analogy to the physics of liquid crystals. In this talk\, I 
 will present a consistent microscopic theoretical model for this nemat
 ic phase and explore its manifestations in a variety of macroscopic pr
 operties of the iron pnictides -- such as elastic\, magnetic\, and tra
 nsport properties. The model is rooted on the degeneracy of the magnet
 ic ground state of these materials\, which\, allied to the coupling to
  the lattice and to the orbital degrees of freedom\, leads to a sponta
 neous tetragonal symmetry breaking in the paramagnetic phase. The scat
 tering of electrons by spin fluctuations in the nematic phase leads to
  an anisotropy in the resistivity\, whose sign changes from electron-d
 oped to hole-doped compounds. Finally\, I will also discuss the impact
  of both nematic order and nematic fluctuations to the unconventional 
 s+- superconducting state of the iron pnictides.
URL:https://www.physics.wisc.edu/events/?id=2997
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