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.
Host:  Greene
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