LAUSR

The quantum capacitance that directly characterizes the density of states of highly mobile Dirac two-dimensional states formed on the surface of a stressed HgTe film is studied experimentally. It is shown that, as opposed to the oscillations in the magnetotransport to which all the existing types of carriers contribute, the quantum oscillations observed in the magnetic capacitance correspond to electrons on the upper surface of the film. Thus, capacitance spectroscopy is a selective technique for studying the properties of an individual topological surface, even when a large number of bulk carriers are present. Because of this feature, for the first time we have obtained data on the phase shift in the Shubnikov-de Haas oscillations usually associated with the Berry phase for an isolated Dirac cone and found its dependence on the location of the Fermi level.