| Summary: | We present thermopower S and resistance R measurements on GaAs-based mesoscopic two-dimensional electron gases as functions of the electron density n _s . At high n _s we observe good agreement between the measured S and S _MOTT , the Mott prediction for a non-interacting metal. As n _s is lowered, we observe a crossover from Mott-like behaviour to that where S shows strong oscillations and even sign changes. Remarkably, there are absolutely no features in R corresponding to those in S . In fact, R is devoid of even any universal conductance fluctuations. A statistical analysis of the thermopower oscillations from two devices of dissimilar dimensions suggest a universal nature of the oscillations. We critically examine whether they can be mesoscopic fluctuations of the kind described by Lesovik and Khmelnitskii (1988 Sov. Phys. JETP http://dx.doi.org/10.1134/s0021364007150131 67 http://dx.doi.org/10.1134/s0021364007150131 ).
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