One-dimensional (1D) interacting electronic systems exhibit distinct properties when compared to their counterparts in higher dimensions. We report Coulomb drag measurements between vertically ...integrated quantum wires separated by a barrier only 15 nanometers wide. The temperature dependence of the drag resistance is measured in the true 1D regime where both wires have less than one 1D subband occupied. As a function of temperature, an upturn in the drag resistance is observed below a temperature T* ∼ 1.6 kelvin. This crossover in Coulomb drag behavior is consistent with Tomonaga-Luttinger liquid models for the 1D-1D drag between quantum wires.
Demonstration of quantum-cascade lasers at ~4.4 THz (~68mum), which are measured to emit 248mW peak power in pulsed mode, and 138mW continuous-wave power at heatsink temperatures of 10K, is reported. ...These lasers are based on a resonant-phonon depopulation scheme, and use a semi-insulating surface-plasmon waveguide.
We report on the first observations of 100 eV to 100 keV electrons over the auroral regions of Jupiter by the Jovian Auroral Distributions Experiment (JADE) on board the Juno mission. The focus is on ...the regions that were magnetically connected to the main auroral oval. Amongst the most remarkable features, JADE observed electron beams, mostly upward going but also some downward going in the south, at latitudes from ~69° to 72° and ~ −66° to −70° corresponding to M shells (“M” for magnetic) from ~18 to 54 and ~28 to 61, respectively. The beams were replaced by upward loss cones at lower latitudes. There was no evidence of strongly accelerated downward electrons analogous to the auroral “inverted Vs” at Earth. Rather, the presence of upward loss cones suggests a diffuse aurora process. The energy spectra resemble tails of distributions or power laws (suggestive of a stochastic acceleration process) but can also have some clear enhancements or even peaks generally between 1 and 10 keV. Electron intensities change on timescales of a second or less at times implying that auroral structures can be of the order of a few tens of kilometers.
Key Points
First 100 eV to 100 keV electron measurements in the auroral regions of Jupiter
Upward and downward electron beams observed in the polar regions and on field lines connected to the middle plasma sheet
Upward loss cone on the field lines connected to the inner plasma sheet suggesting a diffuse aurora process
We report on detailed experimental studies of a high-quality heterojunction insulated-gate field-effect transistor (HIGFET) to probe the particle-hole symmetry of the fractional quantum Hall effect ...(FQHE) states about half-filling in the lowest Landau level. The HIGFET is specially designed to vary the density of a two-dimensional electronic system under constant magnetic fields. We find in our constant magnetic field, variable density measurements that the sequence of FQHE states at filling factors ν=1/3,2/5,3/7… and its particle-hole conjugate states at filling factors 1-ν=2/3,3/5,4/7… have a very similar energy gap. Moreover, a reflection symmetry can be established in the magnetoconductivities between the ν and 1-ν states about half-filling. Our results demonstrate that the FQHE states in the lowest Landau level are manifestly particle-hole symmetric.
Hole transport experiments were performed on a gated double quantum dot device defined in a p-GaAs/AlGaAs heterostructure with a single hole occupancy in each dot. The charging diagram of the device ...was mapped out using charge detection confirming that the single hole limit is reached. In that limit, a detailed study of the two-hole spin system was performed using high bias magnetotransport spectroscopy. In contrast to electron systems, the hole spin was found not to be conserved during interdot resonant tunneling. This allows one to fully map out the two-hole energy spectrum as a function of the magnitude and the direction of the external magnetic field. The heavy-hole g factor was extracted and shown to be strongly anisotropic, with a value of 1.45 for a perpendicular field and close to zero for an in-plane field as required for hybridizing schemes between spin and photonic quantum platforms.
Electron-hole bilayers are expected to make a transition from a pair of weakly coupled two-dimensional systems to a strongly coupled exciton system as the barrier between the layers is reduced. ...Coulomb drag measurements on devices with a 30 nm barrier are consistent with two weakly coupled 2D Fermi systems where the drag decreases with temperature. For a 20 nm barrier, however, we observe an increase in the drag resistance as the temperature is reduced when a current is driven in the electron layer and voltage measured in the hole layer. These results indicate the onset of strong coupling possibly due to exciton formation or phenomena related to exciton condensation.
Heat transport in the quantum Hall regime is investigated using micron-scale heaters and thermometers positioned along the edge of a millimeter-scale two dimensional electron system (2DES). The ...heaters rely on localized current injection into the 2DES, while the thermometers are based on the thermoelectric effect. In the nu=1 integer quantized Hall state, a thermoelectric signal appears at an edge thermometer only when it is "downstream," in the sense of electronic edge transport, from the heater. When the distance between the heater and the thermometer is increased, the thermoelectric signal is reduced, showing that the electrons cool as they propagate along the edge.
Advances in semiconductor bandgap engineering have resulted in the recent development of the terahertz quantum cascade laser. These compact optoelectronic devices now operate in the frequency range ...1.2-5 THz, although cryogenic cooling is still required. Further progress towards the realization of devices operating at higher temperatures and emitting at longer wavelengths (sub-terahertz quantum cascade lasers) is difficult because it requires maintaining a population inversion between closely spaced electronic sub-bands (1 THz approximate 4 meV). Here, we demonstrate a magnetic-field-assisted quantum cascade laser based on the resonant-phonon design. By applying appropriate electrical bias and strong magnetic fields above 16 T, it is possible to achieve laser emission from a single device over a wide range of frequencies (0.68-3.33 THz). Owing to the suppression of inter-Landau-level non-radiative scattering, the device shows magnetic field assisted laser action at 1 THz at temperatures up to 215 K, and 3 THz lasing up to 225 K.
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