Abstract

We report measurements of the dc current ΔI_dc generated across a nanometer-scale constriction, or a quantum point contact (QPC), in the two-dimensional electron gas in the GaAs–GaAlAs system. ΔI_dc was induced by photoexcitation of the QPC in the terahertz regime. To our knowledge, these are the first measurements in which the induced current has been measured as a function of the excitation frequency ω. Spectra of ΔI_dc versus ω were obtained with a time-domain interferometer based on photoconductive (Auston) switch sources of pulsed terahertz radiation. The pulses were coupled to the gate that defines the QPC by a combination of quasi-optical techniques and a novel antenna–transmission-line structure. The spectra are a strong function of the height of the barrier that creates the constriction, which suggests that photon-assisted transport is a possible mechanism for the induced dc current. Measurements of the QPC response demonstrate the applicability of this technique to a variety of other mesoscopic structures, such as single and multiple quantum dots.

© 1994 Optical Society of America

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