Ballistic one-dimensional holes with strong g-factor anisotropy in germanium

We report experimental evidence of ballistic hole transport in one-dimensional quantum wires gate-defined in a strained SiGe/Ge/SiGe quantum well. At zero magnetic field, we observe conductance plateaus at integer multiples of 2e2/h. At finite magnetic field, the splitting of these plateaus by Zeeman effect reveals largely anisotropic g-factors with absolute values below 1 in the quantum-well plane, and exceeding 10 out-of-plane. This g-factor anisotropy is consistent with a heavy-hole character of the propagating valence-band states, which is in line with a predominant confinement in the growth direction. Remarkably, we observe quantized ballistic conductance in device channels up to 600 nm long. These findings mark an important step toward the realization of novel devices for applications in quantum spintronics

The Kondo Effect in the Unitary Limit

We observe a strong Kondo effect in a semiconductor quantum dot when a small magnetic field is applied. The Coulomb blockade for electron tunneling is overcome completely by the Kondo effect and the conductance reaches the unitary-limit value. We compare the experimental Kondo temperature with the theoretical predictions for the spin-1/2 Anderson impurity model. Excellent agreement is found throughout the Kondo regime. Phase coherence is preserved when a Kondo quantum dot is included in one of the arms of an Aharonov-Bohm ring structure and the phase behavior differs from previous results on a non-Kondo dot.Comment: 10 page

Nongalvanic thermometry for ultracold two-dimensional electron domains

Measuring the temperature of a two-dimensional electron gas at temperatures of a few mK is a challenging issue, which standard thermometry schemes may fail to tackle. We propose and analyze a nongalvanic thermometer, based on a quantum point contact and quantum dot, which delivers virtually no power to the electron system to be measured.Comment: 5 pages, 3 figure

Single-electron tunneling in InP nanowires

We report on the fabrication and electrical characterization of field-effect devices based on wire-shaped InP crystals grown from Au catalyst particles by a vapor-liquid-solid process. Our InP wires are n-type doped with diameters in the 40-55 nm range and lengths of several microns. After being deposited on an oxidized Si substrate, wires are contacted individually via e-beam fabricated Ti/Al electrodes. We obtain contact resistances as low as ~10 kOhm, with minor temperature dependence. The distance between the electrodes varies between 0.2 and 2 micron. The electron density in the wires is changed with a back gate. Low-temperature transport measurements show Coulomb-blockade behavior with single-electron charging energies of ~1 meV. We also demonstrate energy quantization resulting from the confinement in the wire.Comment: 4 pages, 3 figure

Evaluating the Thermal Performance of Retrofitted Lightweight Green Roofs and Walls in Sydney and Rio de Janeiro

© 2017 The Authors. With increasing densification in urban settlements, environmental issues are a challenge in the sustainable development of all cities globally. Considering that the built environment releases almost half of the total greenhouse gas emissions, an effective solution to mitigating the impacts of increasing temperatures can be the improved performance of existing buildings. Furthermore 87% of the buildings we will have in 2050 are already built. Retrofitting roofs and walls with a living vegetated system such as green roofs and walls could be an upgrade option, increasing sustainable construction. The benefits are improved thermal performance but also improved air quality, stormwater attenuation, increased bio-diversity and lower heating and / or cooling energy consumption. No empirical data exists for Sydney and Rio de Janeiro and the question is; what is the extent of thermal improvement with retrofitted green walls and roof in timber framed and blockwork structures? This study analyses both effects and benefits of the green roofs and walls through an experiment in two countries: one in Sydney, Australia; a timber framed construction, and another one in Rio de Janeiro, Brazil; with blockwork construction. This difference in the material choice was made according to the most common type of construction for housing in each country. In each site, the walls and the roof of one of the prototypes were covered with plants and compared to the performance of an unplanted but otherwise identical prototype. The thermal performance was analysed by observing the temperature variation simultaneously in a non-vegetated and vegetated structure. The initial findings show that the combination of green roof and green walls have a relevant role in temperature attenuation. These results indicate, that this lightweight retrofit green technology could not only represent an important advance on sustainable development, but can that it also lead to more comfortable internal conditions for humans living in dense urban environments

Pauli spin blockade in CMOS double quantum dot devices

Silicon quantum dots are attractive candidates for the development of scalable, spin-based qubits. Pauli spin blockade in double quantum dots provides an efficient, temperature independent mechanism for qubit readout. Here we report on transport experiments in double gate nanowire transistors issued from a CMOS process on 300 mm silicon-on-insulator wafers. At low temperature the devices behave as two few-electron quantum dots in series. We observe signatures of Pauli spin blockade with a singlet-triplet splitting ranging from 0.3 to 1.3 meV. Magneto-transport measurements show that transitions which conserve spin are shown to be magnetic-field independent up to B = 6 T.Comment: 5 pages , 4 figure