  We have observed Shubnikov-de Haas oscillations in FeSe. The Fermi surface
deviates significantly from predictions of band-structure calculations and most
likely consists of one electron and one hole thin cylinder. The carrier density
is in the order of 0.01 carriers/ Fe, an order-of-magnitude smaller than
predicted. Effective Fermi energies as small as 3.6 meV are estimated. These
findings call for elaborate theoretical investigations incorporating both
electronic correlations and orbital ordering.
