We have used inelastic neutron scattering to examine the magnetic fluctuations at intermediate frequencies in the simplest high temperature superconductor, La_{ 2-x}Sr_{ x}Cu_{ 4}. 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 ~7 meV there is additional scattering present below T_{ c} which is characterised by an extraordinarily long coherence length, in excess of 50 \AA.
Categories: cond-mat