Spin-Resolved Magneto-Tunneling and Giant Anisotropic g-Factor in Broken Gap InAs-GaSb Core-Shell Nanowires.

We experimentally and computationally investigate the magneto-conductance across the radial heterojunction of InAs-GaSb core-shell nanowires under a magnetic field, B, up to 30 T and at temperatures in the range 4.2-200 K. The observed double-peak negative differential conductance markedly blue-shifts with increasing B. The doublet accounts for spin-polarized currents through the Zeeman split channels of the InAs (GaSb) conduction (valence) band and exhibits strong anisotropy with respect to B orientation and marked temperature dependence. Envelope function approximation and a semiclassical (WKB) approach allow to compute the magnetic quantum states of InAs and GaSb sections of the nanowire and to estimate the B-dependent tunneling current across the broken-gap interface. Disentangling different magneto-transport channels and a thermally activated valence-to-valence band transport current, we extract the g-factor from the spin-up and spin-down dI/dV branch dispersion, revealing a giant, strongly anisotropic g-factor in excess of 60 (100) for the radial (tilted) field configurations.

Large Enhancement of Critical Current in Superconducting Devices by Gate Voltage.

Significant control over the properties of a high-carrier density superconductor via an applied electric field has been considered infeasible due to screening of the field over atomic length scales. Here, we demonstrate an enhancement of up to 30% in critical current in a back-gate tunable NbN micro- and nano superconducting bridges. Our suggested plausible mechanism of this enhancement in critical current based on surface nucleation and pinning of Abrikosov vortices is consistent with expectations and observations for type-II superconductor films with thicknesses comparable to their coherence length. Furthermore, we demonstrate an applied electric field-dependent infinite electroresistance and hysteretic resistance. Our work presents an electric field driven enhancement in the superconducting property in type-II superconductors which is a crucial step toward the understanding of field-effects on the fundamental properties of a superconductor and its exploitation for logic and memory applications in a superconductor-based low-dissipation digital computing paradigm.

Gate-Controlled Suspended Titanium Nanobridge Supercurrent Transistor.

Under standard conditions, the electrostatic field-effect is negligible in conventional metals and was expected to be completely ineffective also in superconducting metals. This common belief was recently put under question by a family of experiments that displayed full gate-voltage-induced suppression of critical current in superconducting all-metallic gated nanotransistors. To date, the microscopic origin of this phenomenon is under debate, and trivial explanations based on heating effects given by the negligible electron leakage from the gates should be excluded. Here, we demonstrate the control of the supercurrent in fully suspended superconducting nanobridges. Our advanced nanofabrication methods allow us to build suspended superconducting Ti-based supercurrent transistors which show ambipolar and monotonic full suppression of the critical current for gate voltages of VGC ≃ 18 V and for temperatures up to ∼80% of the critical temperature. The suspended device architecture minimizes the electron-phonon interaction between the superconducting nanobridge and the substrate, and therefore, it rules out any possible contribution stemming from charge injection into the insulating substrate. Besides, our finite element method simulations of vacuum electron tunneling from the gate to the bridge and thermal considerations rule out the cold-electron field emission as a possible driving mechanism for the observed phenomenology. Our findings promise a better understanding of the field effect in superconducting metals.

Higher stability and more predictive fixation with the Femoral Neck System versus Hansson Pins in femoral neck fractures Pauwels II.

OBJECTIVES: To evaluate the biomechanical performance of the Femoral Neck System (FNS) versus the Hansson Pin System (Hansson Pins) with two parallel pins in a Pauwels II femoral neck fracture model with posterior comminution. METHODS: Forty-degree Pauwels II femoral neck fractures AO 31-B2.1 with 15° posterior wedge were simulated in fourteen paired fresh-frozen human femora, followed by instrumentation with either FNS or Hansson Pins in pair-matched fashion. Implant positioning was quantified by measuring shortest implant distances to inferior cortex (DI) and posterior cortex (DP) on anteroposterior and axial X-rays, respectively. Biomechanical testing was performed in 20° adduction and 10° flexion with simulated iliopsoas muscle tension. Progressively increasing cyclic loading was applied until construct failure. Interfragmentary femoral head-to-shaft movements were measured with optical motion tracking. RESULTS: Cycles to 10° varus deformation were significantly higher for FNS (23007 â€‹± â€‹5496) versus Hansson Pins (17289 â€‹± â€‹4686), P â€‹= â€‹0.027. Cycles to 10° femoral head dorsal tilting (FNS: 12765 â€‹± â€‹3425; Hansson Pins: 13357 â€‹± â€‹6104) and cycles to 10° rotation around the femoral neck axis (FNS: 24453 â€‹± â€‹5073; Hansson Pins: 20185 â€‹± â€‹11065) were comparable between the implants, P â€‹≥ â€‹0.314. For Hansson Pins, the outcomes for varus deformation and dorsal tilting correlated significantly with DI and DP, respectively (P â€‹≤ â€‹0.047), whereas these correlations were not significant for FNS (P â€‹≥ â€‹0.310). CONCLUSIONS: From a biomechanical perspective, by providing superior resistance against varus deformation and performing in a less sensitive way to variations in implant placement, the angular stable Femoral Neck System can be considered as a valid alternative to the Hansson Pin System for the treatment of Pauwels II femoral neck fractures. LEVEL OF EVIDENCE: therapeutic, Level V. THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE: The translational potential of this article is to compare the performance of the FNS with Hansson Pins in a AO 31-B2.1 fracture model featuring a 15 posterior wedge to show the implants behavior concerning the dorsal tilting tendency.

A Josephson phase battery.

A classical battery converts chemical energy into a persistent voltage bias that can power electronic circuits. Similarly, a phase battery is a quantum device that provides a persistent phase bias to the wave function of a quantum circuit. It represents a key element for quantum technologies based on phase coherence. Here we demonstrate a phase battery in a hybrid superconducting circuit. It consists of an n-doped InAs nanowire with unpaired-spin surface states, that is proximitized by Al superconducting leads. We find that the ferromagnetic polarization of the unpaired-spin states is efficiently converted into a persistent phase bias φ0 across the wire, leading to the anomalous Josephson effect1,2. We apply an external in-plane magnetic field and, thereby, achieve continuous tuning of φ0. Hence, we can charge and discharge the quantum phase battery. The observed symmetries of the anomalous Josephson effect in the vectorial magnetic field are in agreement with our theoretical model. Our results demonstrate how the combined action of spin-orbit coupling and exchange interaction induces a strong coupling between charge, spin and superconducting phase, able to break the phase rigidity of the system.

Strategy for accurate thermal biasing at the nanoscale.

We analyze the benefits and shortcomings of a thermal control in nanoscale electronic conductors by means of the contact heating scheme. Ideally, this straightforward approach allows one to apply a known thermal bias across nanostructures directly through metallic leads, avoiding conventional substrate intermediation. We show, by using the average noise thermometry and local noise sensing technique in InAs nanowire-based devices, that a nanoscale metallic constriction on a SiO2 substrate acts like a diffusive conductor with negligible electron-phonon relaxation and non-ideal leads. The non-universal impact of the leads on the achieved thermal bias-which depends on their dimensions, shape and material composition-is hard to minimize, but is possible to accurately calibrate in a properly designed nano-device. Our results allow to reduce the issue of the thermal bias calibration to the knowledge of the heater resistance and pave the way for accurate thermoelectric or similar measurements at the nanoscale.

Conductometric Sensing with Individual InAs Nanowires.

In this work, we isolate individual wurtzite InAs nanowires and fabricate electrical contacts at both ends, exploiting the single nanostructures as building blocks to realize two different architectures of conductometric sensors: (a) the nanowire is drop-casted onto-supported by-a SiO2/Si substrate, and (b) the nanowire is suspended at approximately 250 nm from the substrate. We test the source-drain current upon changes in the concentration of humidity, ethanol, and NO2, using synthetic air as a gas carrier, moving a step forward towards mimicking operational environmental conditions. The supported architecture shows higher response in the mid humidity range (50% relative humidity), with shorter response and recovery times and lower detection limit with respect to the suspended nanowire. These experimental pieces of evidence indicate a minor role of the InAs/SiO2 contact area; hence, there is no need for suspended nanostructures to improve the sensing performance. Moreover, the sensing capability of single InAs nanowires for detection of NO2 and ethanol in the ambient atmosphere is reported and discussed.

Self-Assembled InAs Nanowires as Optical Reflectors.

Subwavelength nanostructured surfaces are realized with self-assembled vertically-aligned InAs nanowires, and their functionalities as optical reflectors are investigated. In our system, polarization-resolved specular reflectance displays strong modulations as a function of incident photon energy and angle. An effective-medium model allows one to rationalize the experimental findings in the long wavelength regime, whereas numerical simulations fully reproduce the experimental outcomes in the entire frequency range. The impact of the refractive index of the medium surrounding the nanostructure assembly on the reflectance was estimated. In view of the present results, sensing schemes compatible with microfluidic technologies and routes to innovative nanowire-based optical elements are discussed.

GHz Electroluminescence Modulation in Nanoscale Subwavelength Emitters.

We investigate light emission from nanoscale point-sources obtained in hybrid metal-GaAs nanowires embedding two sharp axial Schottky barriers. Devices are obtained via the formation of Ni-rich metallic alloy regions in the nanostructure body thanks to a technique of controlled thermal annealing of Ni/Au electrodes. In agreement with recent findings, visible-light electroluminescence can be observed upon suitable voltage biasing of the junctions. We investigate the time-resolved emission properties of our devices and demonstrate an electrical modulation of light generation up to 1 GHz. We explore different drive configurations and discuss the intrinsic bottlenecks of the present device architecture. Our results demonstrate a novel technique for the realization of fast subwavelength light sources with possible applications in sensing and microscopy beyond the diffraction limit.