Resonant magnetotunnelling spectroscopy of a quantum loop

We report on tunnelling transport through a novel quantum device consisting of a double barrier structure fabricated as a submicron square loop in the plane of growth. We find two kinds of quantum confinement coexist in such a device: near the current onset, tunelling starts through zero-dimensional states located in the four corners of the loop, whereas at higher bias the resonant current exhibits kinks due to one-dimensional confinement in the arms of the loop. The use of a high magnetic field permits us to measure the binding energy of the dot ground state to the first one-dimensional subband in the connecting wires. This value is then compared to existing theory. Moreover, we show that the different kinds of lateral confinement are not only evidenced in the resonant structure, but also in the scattering assisted replica peaks.