  One of the puzzling aspects of high temperature superconductors is the
prevalence of magnetism in the normal state and the persistence of
superconductivity in very high magnetic fields. Generally, superconductivity
and magnetism are not compatible. But recent neutron scattering results
indicate that antiferromagnetism can appear deep in the superconducting state
in an applied magnetic field. Magnetic fields penetrate a superconductor in the
form of quantized flux lines each one representing a vortex of supercurrents.
Superconductivity is suppressed in the core of the vortex and it has been
suggested that antiferromagnetism might develop there. To address this question
it is important to perform electronic structural studies with spatial
resolution. Here we report on implementation of a high field NMR imaging
experiment that allows spatial resolution of the electronic behavior both
inside and outside the vortex cores. Outside we find strong antiferromagnetic
fluctuations, and localized inside there are electronic states rather different
from those found in conventional superconductors.
