SPIN FLUCTUATIONS IN YBA2CU3O6.6

An important feature of the high-transition-temperature (high-T-c) cop per oxide superconductors is the magnetism that results from the spins associated with the incomplete outer electronic shells (3d(9)) of the copper ions. Fluctuations of these spins give rise to magnetic excita tions of the material, and might mediate the electron pairing that lea ds to superconductivity. If the mechanism for high-T-c superconductivi ty is the same for all copper oxide systems, their spin fluctuations s hould be universal. But so far, the opposite has seemed to be the case : neutron scattering data reveal clear differences between the spin fl uctuations for two major classes of high-T-c materials, La2-xSrxCuO4 ( refs 1-3) and YBa2Cu3O7-x (refs 4-6), whose respective building blocks are CuO2 layers and bilayers. Here we report two-dimensional neutron- scattering imaging of YBa2Cu3O6.6, which reveals that the low-frequenc y magnetic excitations are virtually identical to those of similarly d oped La2-xSrxCuO4. Thus, the high-temperature (T-c less than or simila r to 92 K) superconductivity of the former materials may be related to spatially coherent low-frequency spin excitations that were previousl y thought to be unique to the lower-T-c (<40 K) single-layer La2-xSrxC uO4 family.