Wave-function mixing in strongly confined tunnel-coupled quantum point contacts

We investigate coupling phenomena in quantum point contacts (QPCs) where a particularly strong lateral confinement leads to large separations of the one-dimensional (1D) subbands (above 10 meV). Closely spaced vertically stacked QPCs were defined by atomic-force-microscope nanolithography and wet-chemical etching on a GaAs/AlGaAs double-quantum-well heterostructure with a two-dimensional symmetric-antisymmetric energy gap of 4 meV. Top-gate and back-gate voltage variation in combination with a cooling bias technique was used for tuning the energy spectra of the tunnel-coupled QPCs in order to obtain degeneracies of 1D subbands. We observed clear anticrossings caused by mixing of the 1D wave-functions in grey-scale transconductance plots versus top-gate and back-gate voltage at 4.2 K.