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College Park, Maryland      June 6 - 10 , 2004

M4-A2 (4:15 PM): Quantum Magnetic Excitations from Stripes in Cuprate Superconductors

J. M. Tranquada (Brookhaven National Laboratory), H. Woo (Brookhaven National Laboratory; ISIS, Rutherford Appleton Laboratory), T. G. Perring (ISIS, Rutherford Appleton Laboratory), H. Goka (IMR, Tohoku Univ.), G. D. Gu, G. Xu (Brookhaven National Laboratory), M. Fujita, K. Yamada (IMR, Tohoku Univ.)

The nature of the electronic correlations underlying high-temperature superconductivity in layered cuprates remains a topic of contention. The parent compounds are antiferromagnetic Mott insulators. Superconductivity is achieved by doping these materials with mobile holes, and it coexists with antiferromagnetic fluctuations. In one approach to the coexistence, the holes are believed to self-organize into stripes that alternate with regions of antiferromagnetic insulator. Such an unusual electronic state would necessitate a novel mechanism of superconductivity. Measurements of magnetic excitations in superconducting YBa2Cu3O6+x appear to pose a problem for universal applicability of the stripe picture, as they are incompatible with the predictions for a stripe system based on semiclassical spin waves. To resolve this issue, we have performed neutron scattering measurements over a wide energy range on stripe-ordered La1.875Ba0.125CuO4 using the MAPS spectrometer at ISIS. We find, surprisingly, that the excitation spectrum is quite similar to that found in recent studies of YBa2Cu3O6+x, and that the semiclassical predictions are not relevant. Instead, the measurements at higher energies can be understood in terms of the quantum excitations of a two-leg antiferromagnetic spin ladder, where the ladders are defined by the charge stripes. Thus, our results provide support for theories of superconductivity based on the existence of stripes.

JMT, HW, GDG, and GX are supported by the Office of Science, U.S.Department of Energy under Contract No. DE-AC02-98CH10886.

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