Speaker: Peter Hirschfeld, University of Florida
Time: October 2, 2014 14:00 - 15:00
Impurities can nucleate local magnetic states and give rise to quasi-long-range magnetic order in correlated electron systems. In the Fe-based superconductors, stripe-like (pi,0) order usually prevails in parent compounds, but competes with (pi,pi) antiferromagnetism. I show that in such a situation, unusual emergent defect states (“nematogens”) can be created by nonmagnetic impurities which strongly break C4 symmetry and may be responsible for local nematic defect structures observed by STM, as well as for the transport anisotropy observed in these materials. The unusual temperature dependence of the resistivity and optical conductivity, quite different from conventional spin density wave metals, will also be discussed in the same framework.