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The interlayer coupling, which has a strong influence on the properties of van der Waals heterostructures, strongly depends on the interlayer distance. Although considerable theoretical interest has been demonstrated, experiments exploiting a variable interlayer coupling on nanocircuits are scarce due to the experimental difficulties. Here, we demonstrate a novel method to tune the interlayer coupling using hydrostatic pressure by incorporating van der Waals heterostructure based nanocircuits in piston-cylinder hydrostatic pressure cells with a dedicated sample holder design. This technique opens the way to conduct transport measurements on nanodevices under pressure using up to 12 contacts without constraints on the sample at the fabrication level. Using transport measurements, we demonstrate that a hexagonal boron nitride capping layer provides a good protection of van der Waals heterostructures from the influence of the pressure medium, and we show experimental evidence of the influence of pressure on the interlayer coupling using weak localization measurements on a transitional metal dichalcogenide/graphene heterostructure. [ABSTRACT FROM AUTHOR]

A superconductor is a natural source of spin-entangled spatially separated electron pairs. Although the first Cooper-pair splitter devices have been realized recently, an experimental confirmation of the spin state and the entanglement of the emitted electron pairs has been lacking up to now. In this paper, a method is proposed to confirm the spin-singlet character of individual split Cooper pairs. Two quantum dots (QDs), each of them holding one spin-prepared electron, serve as the detector of the spin state of a single Cooper pair that is forced to split when it tunnels out from the superconductor to the QDs. The number of charges on the QDs, measured at the end of the procedure, carries information on the spin state of the extracted Cooper pair. The method relies on the experimentally established toolkit of QD-based spin qubits: resonant spin manipulation, Pauli blockade, and charge measurement. [ABSTRACT FROM AUTHOR]

Parallel 1D semiconductor channels connected by a superconducting strip constitute the core platform in several recent quantum device proposals that rely, for example, on Andreev processes or topological effects. In order to realize these proposals, the actual material systems must have high crystalline purity, and the coupling between the different elements should be controllable in terms of their interfaces and geometry. A strategy for synthesizing double InAs nanowires by the vapor‐liquid‐solid mechanism using III‐V molecular beam epitaxy is presented. A superconducting layer is deposited onto nanowires without breaking the vacuum, ensuring pristine interfaces between the superconductor and the two semiconductor nanowires. The method allows for a high yield of merged as well as separate parallel nanowires with full or half‐shell superconductor coatings. Their utility in complex quantum devices by electron transport measurements is demonstrated. [ABSTRACT FROM AUTHOR]

We report measurements and analysis of gate-induced electrostatic barriers for electron transport in InAs nanowires. Three types of local gates are analyzed; narrow gates (50-100 nm) located on top of or below the nanowire, and wide gates overlapping the interfaces between nanowire and source and drain electrodes. We find that applying negative potentials to the local gate electrodes induces tunable barriers of up to 0.25 eV and that transport through the wire can be blocked at neutral and slightly positive potentials on the nanowire-contact gates, indicating that built-in barriers can exist at the nanowire-contact interface. The contact gates can be biased to remove the unwanted interface barriers occasionally formed during processing. From the temperature dependence of the conductance, the barrier height is extracted and mapped as a function of gate voltage. Top and bottom gates are similar to each other in terms of electrostatic couplings (lever arms ∼0.1-0.2 eV/ V) and threshold voltages for barrier induction (Vg∼-1 to -2 V), but low temperature gate sweeps suggest that device stability could be affected by the differences in device processing for the two gate geometries. [ABSTRACT FROM AUTHOR]

We present a method to establish inner point contacts with dimensions as small as 100?nm on hexagonal boron nitride (hBN) encapsulated graphene heterostructures by pre-patterning the top-hBN in a separate step prior to dry-stacking. 2- and 4-terminal field effect measurements between different lead combinations are in qualitative agreement with an electrostatic model assuming point-like contacts. The measured contact resistances are 0.5-1.5?kΩ per contact, which is quite low for such small contacts. By applying a perpendicular magnetic field, an insulating behaviour in the quantum Hall regime was observed, as expected for inner contacts. The fabricated contacts are compatible with high mobility graphene structures and open up the field for the realization of several electron optical proposals. [ABSTRACT FROM AUTHOR]

Abstract: High aspect ratio vertical InAs nanowires were mechanically characterized in a scanning electron microscope equipped with two micromanipulators. One, equipped with a calibrated atomic force microscope probe, was used for in-situ static bending of single nanowires along the 〈11–20〉 crystallographic direction. The other one was equipped with a tungsten tip for dynamic resonance excitation of the same nanowires. This setup enabled a direct comparison between the two techniques. The crystal structure was analyzed using transmission electron microscopy, and for InAs nanowires with a hexagonal wutzite crystal structure, the bending modulus value was found to BM=43.5GPa. This value is significantly lower than previously reported for both cubic zinc blende InAs bulk crystals and InAs nanowires. Besides, due to their high resonance quality factor (Q>1200), the wurtzite InAs nanowires are shown to be a promising candidate for sub-femtogram mass detectors. [Copyright &y& Elsevier]

Recent years have brought an explosion of activities in the research of topological aspects of condensed-matter systems. Topological phases of matter are accompanied by protected surface states or exotic degenerate excitations such as Majorana modes or Haldane's localized spinons. Topologically protected degeneracies can, however, also appear in the bulk. An intriguing example is provided by Weyl semimetals, where topologically protected electronic band degeneracies and exotic surface states emerge even in the absence of interactions. Here we demonstrate experimentally and theoretically that Weyl degeneracies appear naturally in an interacting quantum dot system, for specific values of the external magnetic field. These magnetic Weyl points are robust against spin–orbit coupling unavoidably present in most quantum dot devices. Our transport experiments through an InAs double-dot device placed in magnetic field reveal the presence of a pair of Weyl points, exhibiting a robust ground-state degeneracy and a corresponding protected Kondo effect. Weyl semimetals are a class of crystalline materials whose electronic band structure exhibits topologically protected degeneracy points, known as Weyl points. Here, the authors demonstrate both theoretically and experimentally that Weyl points can also be present in the magnetic-field dependent spectrum of a double quantum dot system, enjoying a similar topological protection. [ABSTRACT FROM AUTHOR]

Indium arsenide nanowires (NWs) are a promising platform to fabricate quantum electronic devices, among other advantages they have strong spin-orbit interaction (SOI). The controlled tuning of the SOI is desired in spin-based quantum devices. In this study we investigate the possibility of tuning the SOI by electrostatic fields generated by a back gate and two side gates placed on the opposite sides of the NW. The strength of the SOI is analyzed by weak anti-localization effect. We demonstrate that the strength of the SOI can be strongly tuned up to a factor of 2 with the electric field across the NW, while the average electron density is kept constant. Furthermore, a simple electrostatic model is introduced to calculate the expected change of the SOI. Good agreement is found between the experimental results and the estimated Rashba-type SOI generated by the gate-induced electric field. [ABSTRACT FROM AUTHOR]