Thermopower study in a double bend quantum structure

The thermopower and linear conductance of GaAs/AlGaAs double-bend structures are studied in quantizing magnetic fields up to 4 T at temperatures down to 0.4 K. The electrostatically defined structure consists of a square region with two quasi-one dimensional channels connected at opposite corners of the region. The presence of quasi-bound states was expected in the structure in the regime of ballistic transport. Using an electron-heating technique we observed noticeable oscillations of the thermopower as a function of the gate voltage near the pinchoff. We show, however, that they are related to variable-range hopping and resonant tunnelling via localized states inside the barrier. We also found that the Mort formula for thermopower worked well under our experimental conditions.