Probing the subband structure of dual electron wave guides

One-dimensional (1D) ballistic electronic transport is characterised by a discrete subband structure leading to conductance quantization. Therefore, the electrical properties of dual electron wave guides (EWGs) are determined by two 1D-energy spectra which are either independent of each other for uncoupled EWGs or show splittings of degenerate 1D-subband edges in the case of mode coupling. A detailed understanding of dual EWGs thus requires direct energy spectroscopy. Here, we give an example how transport spectroscopy under dc drain bias may be employed to reveal the 1D-subband structures of two uncoupled 1D-electron systems. Spatially-coincident EWGs are prepared from a two-dimensional (2D) electron gas occupying the 2D-ground and first excited state in a 30∈nm wide GaAs/AlGaAs quantum well. A 125∈nm-wide lateral constriction is defined by nanolithography with an atomic force microscope. Electronic transport is studied in high magnetic fields at 2∈K and under dc drain bias at 4.2∈K. Variation of the 1D-confining potentials is achieved by cooling the sample under gate bias. Spectroscopy of the subband structure leads to a refined knowledge about each confining potential.