Condensed Matter Physics Seminar
2 p.m., Thursday, April 19, 2007
Room 1201, Physics Building
Magnetic Order and Spin Fluctuations in the Cuprate Superconductors
Jeffrey Lynn
(NIST Center for Neutron Research)
Abstract: The magnetic properties of superconductors have a rich
and interesting history, from the strongly detrimental Abrikosov-Gorkov spin
depairing caused by magnetic impurities in "conventional" superconductors, to
the coexistence and competition of magnetic order and superconductivity in
systems such as Chevrel phase materials and rare-earth nickel borocarbides. For
the cuprate superconductors that are the focus of this talk, the "parent" system
is a Mott-Hubbard antiferromagnetic insulator with very strong magnetic
interactions that are two-dimensional in nature. These strong exchange
interactions survive into the superconducting state, yielding highly correlated
electron systems with quantum spin fluctuations (S=1/2) that can be directly
tied to the superconducting state. We will discuss the universal nature of the
spin fluctuations in hole-doped cuprates, the formation of the "resonance" and
it's experimental relationship to the superconducting order parameter, and the
pseudogap and its possible relation to orbital current models. For the
electron-doped materials we will describe our recent discovery of the magnetic
resonance and its behavior as a function of magnetic field, from the fully
superconducting state at H=0 to the magnetically ordered, semiconducting state
for H>Hc2.
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Host: Greene
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