 The oscillations are periodic versus formula_30 and occur because of the quantization of energy levels in the plane perpendicular to a magnetic field, a phenomenon first predicted by Lev Landau.The new states are called Landau levels and are separated by an energy formula_31 where formula_32 is called the cyclotron frequency, formula_33 is the electronic charge, formula_34 is the electron effective mass and formula_35 is the speed of light.In a famous result, Lars Onsager proved that the period of oscillation formula_36 is related to the cross-section of the Fermi surface (typically given in Å−2) perpendicular to the magnetic field direction formula_37 by the equationformula_38.