Unlike normal metals, graphene's longitudinal resistance shows maxima rather than minima for integral values of the Landau filling factor in measurements of the Shubnikov–de Haas oscillations, whereby the term "integral" quantum Hall effect. These oscillations show a phase shift of π, known as Berry's phase. Berry's phase arises due to chirality or dependence (locking) of the pseudospin quantum number on momentum of low-energy electrons near the Dirac points. The temperature dependence of the oscillations reveals that the carriers have a non-zero cyclotron mass, despite their zero effective mass in the Dirac-fermion formalism.