College Park, Maryland      June 6 - 10 , 2004

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MP46: High Resolution Neutron Scattering Experiments on Spin Excitations in SrCu₂(BO₃)₂

S. Haravifard (Department of Physics and Astronomy, McMaster University, Hamilton, ON, Canada), B.D. Gaulin (Department of Physics and Astronomy, McMaster University, Hamilton, ON, Canada; Canadian Institute for Advanced Research, 180 Dundas St. W., Toronto, Ontario, M5G 1Z8, Canada), S.H. Lee (National Institute of Standards and Technology), J.P. Castellan (Department of Physics and Astronomy, McMaster University, Hamilton, ON, Canada), A.J. Berlinsky (Department of Physics and Astronomy, McMaster University, Hamilton, ON, Canada; Canadian Institute for Advanced Research, 180 Dundas St. W., Toronto, Ontario, M5G 1Z8, Canada), H.A. Dabkowska (Department of Physics and Astronomy, McMaster University, Hamilton, ON, Canada), Y. Qiu (National Institute of Standards and Technology; Department of Materials Science and Engineering, University of Maryland), J.R.D. Copley (National Institute of Standards and Technology)

We performed high resolution inelastic neutron scattering measurements on SrCu₂(¹¹BO₃)₂ which has been proposed as a realization of the two dimensional Shastry-Sutherland system with an exact dimer ground state. Measurements were performed on the Disk Chopper Spectrometer (DCS) and the SPINS triple axis spectrometer, located on cold neutron guides at the NIST Center for Neutron Research. Earlier inelastic neutron scattering measurements have identified three bands of excitations. We performed high Q resolution measurements using SPINS which show distinct Q-dependencies for the single and multiple triplet excitations, and that these excitations are largely dispersionless perpendicular to the basal (H,K,0) plane. Since the Q-dependence of the spin excitations show little L dependence, high energy resolution DCS measurements were integrated along L, which then could reveal the dispersion of the three single triplet excitations continuously across the (H,0) direction within its tetragonal basal plane. These correspond to S^z = +1, 0, -1 transitions from the singlet ground state. We also measured the temperature dependence of both the single and double triplet excitations with SPINS, as well as that of the single triplet excitations with DCS. We observe identical temperature dependencies for the single and double triplet excitations and this temperature dependence to the inelastic scattering is well described as the complement of the dc susceptibility of SrCu₂(BO₃)₂.

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