J Phys. Chem. So/ids Vol. 56, No. 12, pp. 1927-1929, 1995
1995 Ekvier ScienceLtd
Printed in Great Britain
0022-3697/95 $9.50 + 0.00
RESONANT NEUTRON SCATTERING FROM YBa2Cu307
B. KEIMER *, HUNG FAI FONG *, D. REZNIK +, F. DOGAN *, LA. AKSAY +
* Dept. of Physics, Princeton University, Princeton, NJ 08544, U.S.A.
t National Institute of Standards and Technology, Gaithersburg, MD 20899, U.S.A.
* Dept. of Chemical Engineering, Princeton University, Princeton, NJ 08544, U.S.A.
Abstract-We have developed a new scattering geometry for magnetic neutron scattering experiments on
YBa2Cu307 in which the phonon background around q - (E, -), Rw - 40meV is significantly reduced.
We use this new approach to study the previously detected &a& magnetic excitation at - 4OmeV in the
superconducting state in detail. The excitation does not shift substantially in energy up to at least 75K
(-0.8T,). Polarized neutron scattering experiments (horizontal minus vertical field) confirm the magnetic
origin of the 40meV excitation and put stringent limits on the magnetic scattering intensity in the normal
Over the past seven years, numerous magnetic neutron scat-
tering experiments on the underdoped Y3a&u30s+x sys-