  Much of what we know about the electronic states of high-temperature
superconductors is due to photoemission and scanning tunneling spectroscopy
studies of the compound Bi2212. The demonstration of well-defined
quasiparticles in the superconducting state has encouraged many theorists to
apply the conventional theory of metals, Fermi-liquid theory, to the cuprates.
In particular, the spin excitations observed by neutron scattering at energies
below twice the superconducting gap energy are commonly believed to correspond
to an excitonic state involving itinerant electrons. Here, we present the first
measurements of the magnetic spectral weight of optimally-doped Bi2212 in
absolute units. The lack of temperature dependence of the local spin
susceptibility across the superconducting transition temperature, T_c, is
incompatible with the itinerant calculations. Alternatively, the magnetic
excitations could be due to local moments, as the magnetic spectrum is similar
to that in LBCO where quasiparticles and local moments coexist.
