ORAL SESSION 5B7: Neutron Scattering and NMR

Friday, Feb. 25, 9:00 a.m. – 11:00 a.m., Regency Room (Hyatt)

Chairs: J. Tranquada (Brookhaven Nat'l. Lab), K. Levin (U Chicago)

5B7.2 Magnetic Order and Spin Dynamics of Pr in PrBa₂Cu₃O₇

J.W. Lynn 1, N. Rosov 1, S.N. Barilo 2, L. Kurnevitch 2, and A. Zhokhov 3. 1 NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899-8562, USA. 2 Institute of Physics of Solids and Semiconductors, Belarus Academy of Sciences, 220072 Minsk, Belarus. 3 Institute of Solid State Physics, Russian Academy of Sciences, Chernogolovka, Russia.

Presenting Author: J.W. Lynn

Magnetic neutron scattering measurements are reviewed for PrBa₂Cu₃O_6+x and compared to related materials that contain Pr. In these materials the magnetic rare earth ordering temperatures are typically an order-of-magnitude higher than for the other rare earths, indicating that exchange interactions dominate the energetics of the magnetic system. For the spin dynamics in Pr123, the strong f-electron hybridization produces non-Fermi liquid-like scattering, which appears to destroy any chance for superconductivity. This behavior contrasts strongly with the sharp crystal field excitations found for the heavy rare earths, as well as with the sharp levels found in other Pr systems.

5B7.3 Static and Dynamical Characters of the Spin Stripes in both the Superconducting (metal) and Spin Glass (insulator)

Yasuo Endoh, Tohoku University, Sendai, Japan

Presenting Author: Y. Endoh

We review our recent neutron scattering results exploring both static and dynamic spin correlations from lightly doped single and double layered Cu oxide superconducters. Elaborated neutron scattering studies by using large single crystals with the excellent quality available could determine the "static 1 dimensional (1D)" spin density wave structure, which must be a direct proof of the charge "stripe" in the 2D CuO₂ lattices in such materials. In the insulating phase, the SDW structure is diagonal or the diagonal charge stripe is established. Then the "diagonal" stripe tranforms to collinear one associated with the insulator - metal transition at x = 0.055 of La_2-xSr_xCuO₄. The spacing of the spin stripe was determined to be related to x in both diagonal and collinear stripes continuously. The confined charge carrier number is a half filled in the very light doped region and goes to a quarter filled with increasing hole doping. Furthermore, spin dynamics in both stripes is robust: In the diagonal stripe, spin excitations are 2D spin wave like mode but in the metallic or superconducting phase, excitations are so unique that the incommensurate wave vector is well difined even in very high energies. The wave vector of such excitations is linearly related to the superconducting transition temperature T_c, which is generic and robust in the high temperature superconducting Cu oxides.

5B7.4 Neutron Scattering from Magnetic Excitations in YBCO and BSCCO

Bernhard Keimer, Max-Planck-Institute of Solid State Research, D-70569 Stuttgart, Germany

Presenting Author: B. Keimer

We review recent progress in neutron scattering from spin excitations in high temperature superconductors. In particular, we were able to detect magnetic excitations in the BSCCO system at different doping levels. We find that the energy of the magnetic resonance peak is reduced in the overdoped regime, a finding that is important for the theoretical interpretation of this collective mode. Other recent results pertain to the interplay between the collective spin dynamics and localized spin-0 (Zn)and spin-1 (Ni) impurities, and to the origin of the incommensurate spin excitations in YBCO.

5B7.6 Inhomogeneous magnetic and electronic state in underdoped high-T_c oxides

J.I. Budnick 1, Ch. Niedermayer 2, C. Bernhard 3, and A. Moodenbaugh 4. 1 Department of Physics, University of Connecticut, Storrs CT 06269. 2 Universität Konstanz, Fakultät für Physik, 78457 Konstanz, Germany. 3 Max-Planck-Institut für Festkörperforschung, 70569 Stuttgart, Germany. 4 Department of Applied Science, Brookhaven National Laboratory, Upton, NY 11977, USA.

Presenting Author: J.I. Budnick