Periodic magnetoconductance fluctuations in triangular quantum dots in the absence of selective probing

We have studied the magnetoconductance of quantum dots with triangular symmetry and areas down to $0.2 \ensuremath{\mu}{\mathrm{m}}^{2},$ made in a high mobility two-dimensional electron gas embedded in a ${\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}\ensuremath{-}\mathrm{A}\mathrm{l}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ heterostructure. Semiclassical simulations show that the gross features in the measured magnetoconductance are caused by ballistic effects. Below 1 K we observe a strong periodic oscillation, which may be explained in terms of the Aharanov-Bohm flux quantization through the area of a single classical periodic orbit. From a numerical and analytical analysis of possible trajectories in hard- and soft-walled potentials, we identify this periodic orbit as the enscribed triangle. Contrary to other recent experiments, this orbit is not accessible by classical processes for the incoming collimated beam.