  We report quantum oscillation measurements on CaFe2As2 under strong magnetic
fields- recently reported to become superconducting under pressures of as
little as a kilobar. The largest observed carrier pocket occupies less than
0.05 % of the paramagnetic Brillouin zone volume- consistent with Fermi surface
reconstruction caused by antiferromagnetism. On comparing several alkali earth
AFe2As2 antiferromagnets (with A=Ca,Sr and Ba), the dependence of both the
Fermi surface cross-sectional area F_alpha and the effective mass m*_alpha of
the primary observed pocket on the antiferromagnetic/structural transition
temperature T_s is found to be consistent with quasiparticles in a conventional
spin-density wave model. These findings suggest that a conventional
spin-density wave exists within close proximity to superconductivity in this
series of compounds, which may have implications for the microscopic origin of
unconventional pair formation.
