128 research outputs found
Gold-free GaAs/GaAsSb heterostructure nanowires grown on silicon
Growth of GaAs/GaAsSb heterostructurenanowires on silicon without the need for gold seed particles is presented. A high vertical yield of GaAsnanowires is first obtained, and then GaAsâSbâËâ segments are successfully grown axially in these nanowires. GaAsSb can also be integrated as a shell around the GaAs core. Finally, two GaAsSb segments are grown inside a GaAsnanowire and passivated using an AlâGaâËâAs shell. It is found that no stacking faults or twin planes occur in the GaAsSb segments.Part of this work was funded by the Swedish Foundation for
Strategic Research SSF, the Swedish Research Council
VR, and the Knut and Alice Wallenberg Foundation
Spectroscopy of spin-orbit quantum bits in indium antimonide nanowires
Double quantum dot in the few-electron regime is achieved using local gating
in an InSb nanowire. The spectrum of two-electron eigenstates is investigated
using electric dipole spin resonance. Singlet-triplet level repulsion caused by
spin-orbit interaction is observed. The size and the anisotropy of
singlet-triplet repulsion are used to determine the magnitude and the
orientation of the spin-orbit effective field in an InSb nanowire double dot.
The obtained results are confirmed using spin blockade leakage current
anisotropy and transport spectroscopy of individual quantum dots.Comment: 5 pages, supplementary material available at
http://link.aps.org/supplemental/10.1103/PhysRevLett.108.16680
Realization of microwave quantum circuits using hybrid superconducting-semiconducting nanowire Josephson elements
We report the realization of quantum microwave circuits using hybrid
superconductor-semiconductor Josephson elements comprised of InAs nanowires
contacted by NbTiN. Capacitively-shunted single elements behave as transmon
qubits with electrically tunable transition frequencies. Two-element circuits
also exhibit transmon-like behavior near zero applied flux, but behave as flux
qubits at half the flux quantum, where non-sinusoidal current-phase relations
in the elements produce a double-well Josephson potential. These hybrid
Josephson elements are promising for applications requiring microwave
superconducting circuits operating in magnetic field.Comment: Main text: 4 pages, 4 figures; Supplement: 10 pages, 8 figures, 1
tabl
Electrical control over single hole spins in nanowire quantum dots
Single electron spins in semiconductor quantum dots (QDs) are a versatile
platform for quantum information processing, however controlling decoherence
remains a considerable challenge. Recently, hole spins have emerged as a
promising alternative. Holes in III-V semiconductors have unique properties,
such as strong spin-orbit interaction and weak coupling to nuclear spins, and
therefore have potential for enhanced spin control and longer coherence times.
Weaker hyperfine interaction has already been reported in self-assembled
quantum dots using quantum optics techniques. However, challenging fabrication
has so far kept the promise of hole-spin-based electronic devices out of reach
in conventional III-V heterostructures. Here, we report gate-tuneable hole
quantum dots formed in InSb nanowires. Using these devices we demonstrate Pauli
spin blockade and electrical control of single hole spins. The devices are
fully tuneable between hole and electron QDs, enabling direct comparison
between the hyperfine interaction strengths, g-factors and spin blockade
anisotropies in the two regimes
Spin-orbit interaction in InSb nanowires
We use magnetoconductance measurements in dual-gated InSb nanowire devices
together with a theoretical analysis of weak antilocalization to accurately
extract spin-orbit strength. In particular, we show that magnetoconductance in
our three-dimensional wires is very different compared to wires in
two-dimensional electron gases. We obtain a large Rashba spin-orbit strength of
corresponding to a spin-orbit energy of
. These values underline the potential of InSb nanowires in
the study of Majorana fermions in hybrid semiconductor-superconductor devices.Comment: Version as accepted for publication as a Rapid in Phys. Rev.
Signatures of Majorana fermions in hybrid superconductor-semiconductor nanowire devices
Majorana fermions are particles identical to their own antiparticles. They
have been theoretically predicted to exist in topological superconductors. We
report electrical measurements on InSb nanowires contacted with one normal (Au)
and one superconducting electrode (NbTiN). Gate voltages vary electron density
and define a tunnel barrier between normal and superconducting contacts. In the
presence of magnetic fields of order 100 mT we observe bound, mid-gap states at
zero bias voltage. These bound states remain fixed to zero bias even when
magnetic fields and gate voltages are changed over considerable ranges. Our
observations support the hypothesis of Majorana fermions in nanowires coupled
to superconductors.Comment: Raw data available at
http://dx.doi.org/10.4121/uuid:8bf81177-2f2b-49c2-aaf5-d36739873dd
Josephson Ï_0-junction in nanowire quantum dots
The Josephson effect describes supercurrent flowing through a junction connecting two superconducting leads by a thin barrier. This current is driven by a superconducting phase difference Ï between the leads. In the presence of chiral and time-reversal symmetry of the Cooper pair tunnelling process2, the current is strictly zero when Ï vanishes. Only if these underlying symmetries are broken can the supercurrent for Ï = 0 be finite. This corresponds to a ground state of the junction being offset by a phase Ï_0, different from 0 or Ï. Here, we report such a Josephson Ï0-junction based on a nanowire quantum dot. We use a quantum interferometer device to investigate phase offsets and demonstrate that Ï_0 can be controlled by electrostatic gating. Our results may have far-reaching implications for superconducting flux- and phase-defined quantum bits as well as for exploring topological superconductivity in quantum dot systems
Effect of the GaAsP shell on optical properties of self-catalyzed GaAs nanowires grown on silicon
We realize growth of self-catalyzed core-shell GaAs/GaAsP nanowires (NWs) on
Si substrates using molecular-beam epitaxy. Transmission electron microscopy
(TEM) of single GaAs/GaAsP NWs confirms their high crystal quality and shows
domination of the zinc-blende phase. This is further confirmed in optics of
single NWs, studied using cw and time-resolved photoluminescence (PL). A
detailed comparison with uncapped GaAs NWs emphasizes the effect of the GaAsP
capping in suppressing the non-radiative surface states: significant PL
enhancement in the core-shell structures exceeding 2000 times at 10K is
observed; in uncapped NWs PL is quenched at 60K whereas single core-shell
GaAs/GaAsP NWs exhibit bright emission even at room temperature. From analysis
of the PL temperature dependence in both types of NW we are able to determine
the main carrier escape mechanisms leading to the PL quench
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