Supercurrent through InAs nanowires with highly transparent superconducting contacts.

One-dimensional superconducting transistors have been fabricated with individual InAs nanowires (NWs) using radio-frequency sputter cleaning followed by in situ metal deposition. Because of the highly transparent contacts formed in between the InAs NWs and the metals, supercurrent, multiple Andreev reflections and Shapiro steps under microwave radiation have been observed. Near pinch-off gate regions, Fabry-Perot interference and a normal conductance quantization with resonant features have been observed, which were found to be correlated with a supercurrent flow.

Giant, level-dependent g factors in InSb nanowire quantum dots.

We report on magnetotransport measurements on InSb nanowire quantum dots. The measurements show that the quantum levels of the InSb quantum dots have giant g factors, with absolute values up to approximately 70, the largest value ever reported for semiconductor quantum dots. We also observe that the values of these g factors are quantum level dependent and can differ strongly between different quantum levels. The presence of giant g factors indicates that considerable contributions from the orbital motion of electrons are preserved in the measured InSb nanowire quantum dots, while the level-to-level fluctuations arise from spin-orbit interaction. We have deduced a value of Delta(SO) = 280 mueV for the strength of spin-orbit interaction from an avoided level crossing between the ground state and first excited state of an InSb nanowire quantum dot with a fixed number of electrons.

Measuring temperature gradients over nanometer length scales.

When a quantum dot is subjected to a thermal gradient, the temperature of electrons entering the dot can be determined from the dot's thermocurrent if the conductance spectrum and background temperature are known. We demonstrate this technique by measuring the temperature difference across a 15 nm quantum dot embedded in a nanowire. This technique can be used when the dot's energy states are separated by many kT and will enable future quantitative investigations of electron-phonon interaction, nonlinear thermoelectric effects, and the efficiency of thermoelectric energy conversion in quantum dots.

A radio frequency single-electron transistor based on an InAs/InP heterostructure nanowire.

We demonstrate radio frequency single-electron transistors fabricated from epitaxially grown InAs/InP heterostructure nanowires. Two sets of double-barrier wires with different barrier thicknesses were grown. The wires were suspended 15 nm above a metal gate electrode. Electrical measurements on a high-resistance nanowire showed regularly spaced Coulomb oscillations at a gate voltage from -0.5 to at least 1.8 V. The charge sensitivity was measured to 32 microe rms Hz(-1/2) at 1.5 K. A low-resistance single-electron transistor showed regularly spaced oscillations only in a small gate-voltage region just before carrier depletion. This device had a charge sensitivity of 2.5 microe rms Hz(-1/2). At low frequencies this device showed a typical 1/f noise behavior, with a level extrapolated to 300 microe rms Hz(-1/2) at 10 Hz.

Nanowire single-electron memory.

We demonstrate storage of electrons in semiconductor nanowires epitaxially grown from Au nanoparticles. The nanowires contain multiple tunnel junctions (MTJs) of InP barriers and InAs quantum dots designed such that the metal seed particles act as storage nodes. By positioning a second nanowire close to the seed particle it is possible to detect tunneling of individual electrons through the MTJ at 4.2 K. A strong memory effect is observed in the detector current when sweeping the writing voltage.