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We investigate the tunnel coupling between the outer p-type GaAsSb shell and the n-type InAs core in catalyst-free InAs/InP/GaAsSb core-dualshell nanowires. We present a device fabrication protocol based on wet-etching processes on selected areas of the nanostructures that enables multiple configurations of measurements in the same nanowire-based device (i.e. shell-shell, core-core and core-shell). Low-temperature (4.2 K) transport in the shell-shell configuration in nanowires with 5 nm-thick InP barrier reveals a weak negative differential resistance. Differently, when the InP barrier thickness is increased to 10 nm, this negative differential resistance is fully quenched. The electrical resistance between the InAs core and the GaAsSb shell, measured in core-shell configuration, is significantly higher with respect to the resistance of the InAs core and of the GaAsSb shell. The field effect, applied via a back-gate, has an opposite impact on the electrical transport in the core and in the shell portions. Our results show that electron and hole free carriers populate the InAs and GaAsSb regions respectively and indicate InAs/InP/GaAsSb core-dualshell nanowires as an ideal system for the investigation of the physics of interacting electrons and holes at the nanoscale. [ABSTRACT FROM AUTHOR]

We demonstrated device architectures implementing suspended InAs nanowires for thermal conductivity measurements. To this aim, we exploited a fabrication protocol involving the use of a sacrificial layer. The relatively large aspect ratio of our nanostructures combined with their low electrical resistance allows to exploit the four-probe 3ω technique to measure the thermal conductivity, inducing electrical self-heating in the nanowire at frequency ω and measuring the voltage drop across the nanostructure at frequency 3ω. In our systems, field effect modulation of the transport properties can be achieved exploiting fabricated side-gate electrodes in combination with the SiO2/Si ++ substrate acting as a back gate. Our device architectures can open new routes to the all-electrical investigation of thermal parameters in III-V semiconductor nanowires, with a potential impact on thermoelectric applications. [ABSTRACT FROM AUTHOR]

We demonstrate an original method based on controlled oxidation for creating high-quality tunnel junctions between superconducting Al reservoirs and InAs semiconductor nanowires (NWs). We show clean tunnel characteristics with a current suppression by >4 orders of magnitude for a junction bias well below the Al gap of Δ ≈ 200 μeV. The experimental data agree well with the Bardeen-Cooper-Schrieffer theoretical expectations for a superconducting tunnel junction. The studied devices employ small-scale tunnel contacts functioning as thermometers as well as larger electrodes that provide proof-of-principle active cooling of the electron distribution in the NWs. A peak refrigeration of approximately δ T = 10 mK is achieved at a bath temperature of T ≈ 250-350 mK for our prototype devices. This method introduces important perspectives for the investigation of the thermoelectric effects in semiconductor nanostructures and for nanoscale refrigeration. [ABSTRACT FROM AUTHOR]

Nanowires (NWs) are ideal nanostructures for exploring the effects of low dimensionality and thermal conductivity suppression on thermoelectric behavior. However, it is challenging to accurately measure temperature gradients and heat flow in such systems. Here, using a combination of spatially resolved Raman spectroscopy and transport measurements, we determine all the thermoelectric properties of single Se-doped InSb NWs and quantify the figure of merit ZT. The measured laser-induced heating in the NWs and associated electrical response are well described by a 1D heat equation model. Our method allows the determination of the thermal contact resistances at the source and drain electrodes of the NW, which are negligible in our system. The measured thermoelectric parameters of InSb NWs agree well with those obtained based on field-effect transistor Seebeck measurements. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

We investigate a new architecture for the implementation of Josephson junctions combining high critical temperature superconductors (HTS) and semiconductor (Sm) nanowires (NWs). The devices are obtained starting from pre-patterned YBaCuO (YBCO) electrodes and assembling suspended InAs-NWs bridges between nearby superconductive banks. Such a non-standard approach is necessary in the case of HTS since growth conditions for cuprates are incompatible with thermal stability of the Sm nanostructures. We investigate the device behavior as a function of the length L of the InAs bridge. For L > 200 nm, all junctions display a tendency to insulation at low temperatures. For L ∼ 200 nm, a metallic-like behavior is obtained, signaling the possible onset of a superconductive transition of the junction. Technological limitations on the width of the gap separating the YBCO banks currently prevent a further scaling. Our results suggest that a further reduction of the size of the trench between the YBCO electrodes can lead to functional YBCO/InAs-NWs/YBCO Josephson junctions. [ABSTRACT FROM AUTHOR]

The control of orbitals and spin states of single electrons is a key ingredient for quantum information processing and novel detection schemes and is, more generally, of great relevance for spintronics. Coulomb and spin blockade in double quantum dots enable advanced single-spin operations that would be available even for room-temperature applications with sufficiently small devices. To date, however, spin operations in double quantum dots have typically been observed at sub-kelvin temperatures, a key reason being that it is very challenging to scale a double quantum dot system while retaining independent field-effect control of individual dots. Here, we show that the quantum-confined Stark effect allows two dots only 5 nm apart to be independently addressed without the requirement for aligned nanometre-sized local gating. We thus demonstrate a scalable method to fully control a double quantum dot device, regardless of its physical size. In the present implementation we present InAs/InP nanowire double quantum dots that display an experimentally detectable spin blockade up to 10 K. We also report and discuss an unexpected re-entrant spin blockade lifting as a function of the magnetic field intensity. [ABSTRACT FROM AUTHOR]

We demonstrate very large and uniform temperature gradients up to about 1 K every 100 nm, in an architecture which is compatible with the field-effect control of the nanostructure under test. The temperature gradients demonstrated greatly exceed those typically obtainable with standard resistive heaters fabricated on top of the oxide layer. The nanoheating platform is demonstrated in the specific case of a short-nanowire device. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The controlled tailoring of the energy distribution in an electron system opens the way to interesting new physics and device concepts, as demonstrated by research on metallic nanodevices during recent years. Here we investigate how Josephson coupling in a superconductor-InAs nanowire junction can be tuned by means of hot-electron injection and we show that a complete suppression of superconductive effects can be achieved using a power as low as 100 pW. Nanowires offer a novel design freedom as they allow axial and radial heterostructures to be defined as well as control over doping profiles, which can be crucial in the development of devices-such as nanorefrigerators-where precisely controlled and predictable energy barriers are mandatory. Our work provides estimates for unknown key thermal and electrical parameters, such as the electron-phonon coupling, in our InAs nanostructures. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Near-field imaging with terahertz (THz) waves is emerging as a powerful technique for fundamental research in photonics and across physical and life sciences. Spatial resolution beyond the diffraction limit can be achieved by collecting THz waves from an object through a small aperture placed in the near-field. However, light transmission through a sub-wavelength size aperture is fundamentally limited by the wave nature of light. Here, we conceive a novel architecture that exploits inherently strong evanescent THz field arising within the aperture to mitigate the problem of vanishing transmission. The sub-wavelength aperture is originally coupled to asymmetric electrodes, which activate the thermo-electric THz detection mechanism in a transistor channel made of flakes of black-phosphorus or InAs nanowires. The proposed novel THz near-field probes enable room-temperature sub-wavelength resolution coherent imaging with a 3.4 THz quantum cascade laser, paving the way to compact and versatile THz imaging systems and promising to bridge the gap in spatial resolution from the nanoscale to the diffraction limit. [ABSTRACT FROM AUTHOR]