  Quantum oscillations in the binary antiferromagnetic metal FeAs are presented
and compared to theoretical predictions for the electronic band structure in
the anomalous spin density wave state of this material. Demonstrating a new
method for growing single crystals out of Bi flux, we utilize the highest
quality FeAs to perform torque magnetometry experiments up to 35 T, using
rotations of field angle in two planes to provide evidence for one electron and
one hole band in the magnetically ordered state. The resulting picture agrees
with previous experimental evidence for multiple carriers at low temperatures,
but the exact Fermi surface shape differs from predictions, suggesting that
correlations play a role in deviation from ab initio theory and cause up to a
four-fold enhancement in the effective carrier mass.
