New magnetic coherence effect in superconducting La2-xSrxCuO4

We have used inelastic neutron scattering to examine the magnetic fluctuations at intermediate frequencies in the simplest high temperature superconductor, La2-xSrxCuO4. The suppression of the low energy magnetic response in the superconducting state is accompanied by an increase in the response at higher energies. Just above a threshold energy of similar to 7 meV there is additional scattering present below T-c which is characterized by an extraordinarily long coherence length, in excess of 50 Angstrom.