We describe the operation of, and demonstrate logic functionality in, networks of physically coupled, nanometer-scale magnets designed for digital computation in magnetic quantum-dot cellular automata (MQCA) systems. MQCA offer low power dissipation and high integration density of functional elements and operate at room temperature. The basic MQCA logic gate, that is, the three-input majority logic gate, is demonstrated.

This paper presents an experimental demonstration of a basic cell of the quantum-dot cellular automata, a transistorless approach to computation that addresses the issues of device density, interconnection, and power dissipation. The device under study was composed of four metal dots, connected with tunnel junctions and capacitors, and operated at <50 mK. Operation was evidenced by switching of a single electron between output dots controlled by a single electron switching in input dots, demonstrating a nonlinear, bistable response.

We investigated two-dimensional electron transport in doped AlGaN–GaN heterostructures (with the electron sheet concentration $n_s{\text{≈10}}^{13}\hspace{0.17em}{\mathrm{cm}}^{\mathrm{-2}}$ ) grown on conducting 6H–SiC substrates in the temperature range $\text{T=0.3–300\hspace{0.17em}}\mathrm{K}.$ The electron mobility in AlGaN–GaN heterostructures grown on SiC was higher than in those on sapphire substrates, especially at cryogenic temperatures. The highest measured Hall mobility at room temperature was ${\mu }_H\text{=2019\hspace{0.17em}}{\mathrm{cm}}^{\mathrm{2}}\mathrm{/V\hspace{0.17em}s}.$ At low temperatures, the electron mobility increased approximately five times and saturated below 10 K at ${\mu }_H\text{=10250\hspace{0.17em}}{\mathrm{cm}}^{\mathrm{2}}\mathrm{/V\hspace{0.17em}s}.$ The experimental results are compared with the electron mobility calculations accounting for various electron scattering mechanisms.

We report on the measurements of the electron mobility in modulation-doped ${\mathrm{Al}}_{\mathrm{0.2}}{\mathrm{Ga}}_{\mathrm{0.8}}\mathrm{N–GaN}$ heterostructures grown on sapphire, conducting 6H–SiC, and insulating 4H–SiC substrates as a function of the sheet electron density, $n_s,$ at the heterointerface in a wide temperature range. The mobility increases with an increase in $n_s$ up to approximately ${\text{1×10}}^{13} {\mathrm{cm}}^{\mathrm{-2}}$ and decreases with a further increase in $n_s.$ This is explained by the electron spillover at high values of $n_s$ from the two-dimensional states at the AlGaN/GaN heterointerface into the delocalized states in the doped GaN channel. The maximum electron Hall mobility in excess of $\text{2000\hspace{0.05em}}{\mathrm{cm}}^{\mathrm{2}}\mathrm{/V s}$ at room temperature and $\text{11\hspace{0.05em}000\hspace{0.05em}}{\mathrm{cm}}^{\mathrm{2}}\mathrm{/V s}$ at 4.2 K was measured in the heterostructures grown on 6H–SiC at the values of $n_s$ close to ${10}^{13} {\mathrm{cm}}^{\mathrm{-2}}$ and ${\text{7×10}}^{12} {\mathrm{cm}}^{\mathrm{-2}},$ respectively.

Experimental studies are presented of a binary wire based on the quantum-dot cellular automata computational paradigm. The binary wire consists of capacitively coupled double-dot cells charged with single electrons. The polarization switch caused by an applied input signal in one cell leads to the change in polarization of the adjacent cell and so on down the line, as in falling dominos. Wire polarization was measured using single islands as electrometers. Experimental results are in very good agreement with the theory and confirm there are no metastable states in the wire.