Letter abstract
Nature Physics 5, 642 - 646 (2009)
Published online: 2 August 2009 | doi:10.1038/nphys1360
Subject Category: Condensed-matter physics
Testing the itinerancy of spin dynamics in superconducting Bi2Sr2CaCu2O8+
Guangyong Xu1, G. D. Gu1, M. Hücker1, B. Fauqué2, T. G. Perring3,4, L. P. Regnault5 & J. M. Tranquada1
Much of what we know about the electronic states of high-temperature superconductors is due to photoemission1, 2, 3 and scanning tunnelling spectroscopy4, 5 studies of the compound Bi2Sr2CaCu2O8+
. The demonstration of well-defined quasiparticles in the superconducting state has encouraged many theorists to apply the conventional theory of metals, Fermi-liquid theory, to the cuprates6, 7, 8, 9. In particular, the spin excitations observed by neutron scattering at energies below twice the superconducting gap energy are commonly believed to correspond to an excitonic state involving itinerant electrons10, 11, 12, 13, 14. Here, we present the first measurements of the magnetic spectral weight of optimally doped Bi2Sr2CaCu2O8+ in absolute units. The lack of temperature dependence of the local spin susceptibility across the superconducting transition temperature, Tc, is incompatible with the itinerant calculations. Alternatively, the magnetic excitations could be due to local moments, as the magnetic spectrum is similar to that in La1.875Ba0.125CuO4 (ref. 15), where quasiparticles16 and local moments17 coexist.
- Brookhaven National Laboratory, Upton, New York 11973-5000, USA
- Laboratoire Léon Brillouin, CEA-CNRS, CEA-Saclay, 91191 Gif sur Yvette, France
- ISIS Facility, STFC Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX, UK
- Department of Physics, University College London, Gower Street, London WC1E 6BT, UK
- CEA-Grenoble, INAC-SPSMS-MDN, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France
Correspondence to: J. M. Tranquada1 e-mail: jtran@bnl.gov
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