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The topological insulator is a unique state of matter that possesses a metallic surface state of massless particles known as Dirac fermions, which have coupled spin and momentum quantum numbers. Owing to the preservation of time-reversal symmetry, this coupling protects the wavefunctions against disorder^,,. The experimental realization of this state of matter in Bi₂Se₃ and Bi₂Te₃ has sparked considerable interest owing both to their potential use in spintronic devices and in the investigation of the fundamental nature of topologically non-trivial quantum matter. However, the conductivity of these compounds tends to be dominated by the bulk of the material because of chemical imperfection, making the transport properties of the surface nearly impossible to measure. We have systematically reduced the number of bulk carriers in Bi₂Se₃ to the point where a magnetic field can collapse them to their lowest Landau …