 States with the same formula_22 but different formula_23 are degenerate.The density of states collapses from the constant for the two-dimensional electron gas (density of states per unit surface at a given energy taking into account degeneration due to spin formula_26) to a series of formula_27-functions called Landau levels separated formula_28.In a real system, however, the Landau levels acquire a width formula_29 being formula_30 the time between scattering events.