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We report on combined measurements of heat and charge transport through a single-electron transistor. The device acts as a heat switch actuated by the voltage applied on the gate. The Wiedemann-Franz law for the ratio of heat and charge conductances is found to be systematically violated away from the charge degeneracy points. The observed deviation agrees well with the theoretical expectation. With large temperature drop between the source and drain, the heat current away from degeneracy deviates from the standard quadratic dependence in the two temperatures.
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We report on experimental results for the conductance of metallic single-electron transistors as a function of temperature, gate voltage and dimensionless conductance. In contrast to previous experiments our transistor layout allows for a direct measurement of the parallel conductance and no ad hoc assumptions on the symmetry of the transistors are necessary. Thus we can make a comparison between our data and theoretical predictions without any adjustable parameter. Even for rather weakly conducting transistors significant deviations from the perturbative results are noted. On the other hand, path integral Monte Carlo calculations show remarkable agreement with experiments for the whole range of temperatures and conductances.
We present a linear-response theory for the thermopower of a single-electron transistor consisting of a superconducting island weakly coupled to two normal-conducting leads (NSN SET). The thermopower shows oscillations with the same periodicity as the conductance and is rather sensitive to the size of the superconducting gap. In particular, the previously studied sawtooth-like shape of the thermopower for a normal-conducting single-electron device is qualitatively changed even for small gap energies.
Single dopants in semiconductor nanostructures have been studied in great details recently as they are good candidates for quantum bits, provided they are coupled to a detector. Here we report coupling of a single As donor atom to a single-electron transistor (SET) in a silicon nanowire field-effect transistor. Both capacitive and tunnel coupling are achieved, the latter resulting in a dramatic increase of the conductance through the SET, by up to one order of magnitude. The experimental results are well explained by the rate equations theory developed in parallel with the experiment.
Starting from the Kubo formula for conductance, we calculate the frequency-dependent response of a single-electron transistor (SET) driven by an ac signal. Treating tunneling processes within the lowest order approximation, valid for a wide range of parameters, we discover a finite reactive part even under Coulomb blockade due to virtual processes. At low frequencies this can be described by an effective capacitance. This effect can be probed with microwave reflection measurements in radio-frequency (rf) SET provided that the capacitance of the surroundings does not completely mask that of the SET.
The fundamental property of most single-electron devices with quasicontinuous quasiparticle spectrum on the island is the periodicity of their transport characteristics in the gate voltage. This property is robust even with respect to placing the ferroelectric insulators in the source and drain tunnel junctions. We show that placing the ferroelectric inside the gate capacitance breaks this periodicity. The current-voltage characteristics of this SET strongly depends on the ferroelectric polarization and shows the giant memory-effect even for negligible ferroelectric hysteresis making this device promising for memory applications.
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