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Summary: VOLUME 78, NUMBER 4 P H Y S I C A L R E V I E W L E T T E R S 27 JANUARY 1997
Superconductivity-Induced Anomalies in the Spin Excitation Spectra
of Underdoped YBa2Cu3O61x
H. F. Fong and B. Keimer
Department of Physics, Princeton University, Princeton, New Jersey 08544
and Brookhaven National Laboratory, Upton, New York 11973
D. L. Milius and I. A. Aksay
Department of Chemical Engineering, Princeton University, Princeton, New Jersey 08544
(Received 23 August 1996)
Polarized and unpolarized neutron scattering have been used to determine the effect of superconduc-
tivity on the magnetic excitation spectra of YBa2Cu3O6.5 Tc 52 K and YBa2Cu3O6.7 Tc 67 K .
Pronounced enhancements of the spectral weight centered around 25 and 33 meV, respectively, are
observed below Tc in both crystals, compensated predominantly by a loss of spectral weight at higher
energies. The data provide important clues to the origin of the 40 meV magnetic resonance peak in
YBa2Cu3O7. [S0031-9007(96)02291-0]
PACS numbers: 74.25.Jb, 74.25.Kc, 74.72.Bk
Recently a new magnetic resonance mode has been
found in the superconducting state of YBa2Cu3O7 by
inelastic neutron scattering. The mode occurs at an
energy of 40 meV and wave vector q p a, p a , and
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