Density-dependent thermopower oscillations in mesoscopic two-dimensional electron gases

Abstract

We present thermopower $S$ and resistance $R$ measurements on GaAs-based\nmesoscopic two-dimensional electron gases (2DEGs) as functions of the electron\ndensity $n_s$. At high $n_s$ we observe good agreement between the measured $S$\nand $S_{\\rm{MOTT}}$, the Mott prediction for a non-interacting metal. As $n_s$\nis lowered, we observe a crossover from Mott-like behaviour to that where $S$\nshows strong oscillations and even sign changes. Remarkably, there are\nabsolutely no features in $R$ corresponding to those in $S$. In fact, $R$ is\ndevoid of even any universal conductance fluctuations. A statistical analysis\nof the thermopower oscillations from two devices of dissimilar dimensions\nsuggest a universal nature of the oscillations. We critically examine whether\nthey can be mesoscopic fluctuations of the kind described by Lesovik and\nKhmelnitskii in Sov. Phys. JETP. \\textbf{67}, 957 (1988).\n