  Superconducting transitions are driven by thermal fluctuations close to the
transition temperature, Tc. These fluctuations are averaged out in global
measurements, leaving imprints on susceptibility and resistance measurements.
Here, we use a scanning superconducting quantum interference device to image
thermal superconducting fluctuations in Nb, a conventional BCS superconductor.
We observe fluctuations in both space and time which manifest themselves as
grains of weaker and stronger diamagnetic response, exhibiting telegraph-like
noise as a function of time. Local fluctuations are also found in the imaginary
component of the susceptibility demonstrating that the local vortex dissipation
can also be used as a probe of the fluctuations. An important outcome of our
measurements is the observation and realization that the susceptibility
decrease to zero as the temperature is raised towards Tc always occurs in
quantized steps irrespective of the sample geometry. The technique described
here is expected to be a useful tool for studying the nature of fluctuations in
more complex superconductors, providing important information on critical
properties such as fluctuation length, time scales, and local viscosity.
