University of Minnesota
School of Physics & Astronomy

Condensed Matter Seminar

Thursday, November 12th 2009
1:25 pm:
Condensed Matter Seminar in 210 Physics
Speaker: Martin Greven, University of Minnesota
Subject: Novel magnetic excitations in the pseudogap phase of a cuprate superconductor

Magnetic correlations might cause the superconductivity in the cuprates, and they are generally believed to be antiferromagnetic and to arise from the underlying copper-oxygen planes. Using neutron scattering on the model compound HgBa2CuO4+δ, we recently discovered the existence of a prominent magnetic excitation with unusual characteristics: (i) the excitation appears to involve active degrees of freedom on both planar and apical oxygen; (ii) it is present throughout the entire Brillouin zone; (iii) it exhibits a weak doping dependence and dispersion, and (iv) a maximum energy of 56 meV at the antiferromagnetic point, where it meets the magnetic resonance, a well-known spin-one excitation that appears in the superconducting state; (v) furthermore, unlike the resonance, the new exciation maintains its integrity in the normal state up to the pseudogap temperature (T*), and thus appears to be associated with the novel magnetic order recently identified in the pseudogap phase. I will also discuss our recent finding of a universal relationship between the magnetic resonance energy (Er) and the superconducting pairing gap (&Delta) that is valid for the three different classes of unconventional superconductors, ranging from being close to the Mott-insulating limit to being on the border of itinerant magnetism.

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