  We study orbital magnetism of a degenerate electron gas in a number of
two-dimensional integrable systems, within linear response theory. There are
three relevant energy scales: typical level spacing, the energy related to the
inverse time of flight across the system, and the Fermi energy.
Correspondingly, there are three distinct temperature regimes: microscopic,
mesoscopic, and macroscopic. In the first two regimes there are large
finite-size effects in the magnetic susceptibility, whereas in the third regime
the susceptibility approaches its macroscopic value. In some cases, such as a
quasi-one-dimensional strip or a harmonic confining potential, it is possible
to obtain analytic expressions for the susceptibility in the entire temperature
range.
