[Show abstract][Hide abstract]ABSTRACT: Coupled quantum dots in series have been realized in two dimensional electron
gas (2DEG) in GaAs/AlGaAs heterostructures using the surface gate, and transport
measurements have been performed at the dilution refrigerator temperature. The
electrical transport was found to be determined by the Coulomb blockade and the
resonant tunneling. The energy width of the resonant peak can be smaller than the
thermal energy when two dots are sufficiently isolated. The charge stability diagram, by
changing two gates attached to each dot, was measured for weak and strong coupling
conditions. The width of the current resonant peak changed significantly as the coupling
was increased, while the capacitive coupling did not change so much. The experimental
result was analyzed using a simple capacitance model.
Preview · Article · Dec 1998 · Japanese Journal of Applied Physics
[Show abstract][Hide abstract]ABSTRACT: Quantum dots are small conductive regions in a semiconductor, containing a variable number of electrons (N=1 to 1000) that occupy well defined discrete quantum states. They are often referred to as artificial atoms with the unique property that they can be connected to current and voltage contacts. This allows one to use transport measurements to probe the discrete energy spectra. To continue the analogy with atoms, two quantum dots can be connected to form an 'artificial molecule'. Depending on the strength of the inter-dot coupling, the two dots can have an ionic binding (i.e. electrons are localized on the individual dots) or a covalent binding (i.e. electrons are delocalized over both dots). The covalent binding leads to a bonding and an anti-bonding state with an energy splitting proportional to the tunnel coupling. In the dc current response to microwave excitation we observe a transition from an ionic bonding to a covalent bonding, when we vary the inter-dot coupling strength. This demonstrates controllable quantum coherence in single electron devices.