Spin transport in ferromagnet-InSb nanowire quantum devices

Signatures of Majorana zero modes (MZMs), which are the building blocks for fault-tolerant topological quantum computing, have been observed in semiconductor nanowires (NW) with strong spin-orbital-interaction (SOI), such as InSb and InAs NWs with proximity-induced superconductivity. Realizing topological superconductivity and MZMs in this most widely-studied platform also requires eliminating spin degeneracy, which is realized by applying a magnetic field to induce a helical gap. However, the applied field can adversely impact the induced superconducting state in the NWs and also places geometric restrictions on the device, which can affect scaling of future MZM-based quantum registers. These challenges could be circumvented by integrating magnetic elements with the NWs. With this motivation, in this work we report the first experimental investigation of spin transport across InSb NWs, which are enabled by devices with ferromagnetic (FM) contacts. We observe signatures of spin polarization and spin-dependent transport in the quasi-one-dimensional ballistic regime. Moreover, we show that electrostatic gating tunes the observed magnetic signal and also reveals a transport regime where the device acts as a spin filter. These results open an avenue towards developing MZM devices in which spin degeneracy is lifted locally, without the need of an applied magnetic field. They also provide a path for realizing spin-based devices that leverage spin-orbital states in quantum wires.Comment: 30 pages, 12 figure

Selective Area Superconductor Epitaxy to Ballistic Semiconductor Nanowires

Semiconductor nanowires such as InAs and InSb are promising materials for studying Majorana zero-modes and demonstrating non-Abelian particle exchange relevant for topological quantum computing. While evidence for Majorana bound states in nanowires has been shown, the majority of these experiments are marked by significant disorder. In particular, the interfacial inhomogeneity between the superconductor and nanowire is strongly believed to be the main culprit for disorder and the resulting soft superconducting gap ubiquitous in tunneling studies of hybrid semiconductor-superconductor systems. Additionally, a lack of ballistic transport in nanowire systems can create bound states that mimic Majorana signatures. We resolve these problems through the development of selective-area epitaxy of Al to InSb nanowires, a technique applicable to other nanowires and superconductors. Epitaxial InSb-Al devices generically possess a hard superconducting gap and demonstrate ballistic 1D superconductivity and near perfect transmission of supercurrents in the single mode regime, requisites for engineering and controlling 1D topological superconductivity. Additionally, we demonstrate that epitaxial InSb-Al superconducting island devices, the building blocks for Majorana based quantum computing applications, prepared using selective area epitaxy can achieve micron scale ballistic 1D transport. Our results pave the way for the development of networks of ballistic superconducting electronics for quantum device applications

Attosecond control of electrons emitted from a nanoscale metal tip

Attosecond science is based on steering of electrons with the electric field of well-controlled femtosecond laser pulses. It has led to, for example, the generation of XUV light pulses with a duration in the sub-100-attosecond regime, to the measurement of intra-molecular dynamics by diffraction of an electron taken from the molecule under scrutiny, and to novel ultrafast electron holography. All these effects have been observed with atoms or molecules in the gas phase. Although predicted to occur, a strong light-phase sensitivity of electrons liberated by few-cycle laser pulses from solids has hitherto been elusive. Here we show a carrier-envelope (C-E) phase-dependent current modulation of up to 100% recorded in spectra of electrons laser-emitted from a nanometric tungsten tip. Controlled by the C-E phase, electrons originate from either one or two sub-500as long instances within the 6-fs laser pulse, leading to the presence or absence of spectral interference. We also show that coherent elastic re-scattering of liberated electrons takes place at the metal surface. Due to field enhancement at the tip, a simple laser oscillator suffices to reach the required peak electric field strengths, allowing attosecond science experiments to be performed at the 100-Megahertz repetition rate level and rendering complex amplified laser systems dispensable. Practically, this work represents a simple, exquisitely sensitive C-E phase sensor device, which can be shrunk in volume down to ~ 1cm3. The results indicate that the above-mentioned novel attosecond science techniques developed with and for atoms and molecules can also be employed with solids. In particular, we foresee sub-femtosecond (sub-) nanometre probing of (collective) electron dynamics, such as plasmon polaritons, in solid-state systems ranging in size from mesoscopic solids via clusters to single protruding atoms.Comment: Final manuscript version submitted to Natur

Quantized Majorana conductance

Majorana zero-modes hold great promise for topological quantum computing. Tunnelling spectroscopy in electrical transport is the primary tool to identify the presence of Majorana zero-modes, for instance as a zero-bias peak (ZBP) in differential-conductance. The Majorana ZBP-height is predicted to be quantized at the universal conductance value of 2e2/h at zero temperature. Interestingly, this quantization is a direct consequence of the famous Majorana symmetry, 'particle equals antiparticle'. The Majorana symmetry protects the quantization against disorder, interactions, and variations in the tunnel coupling. Previous experiments, however, have shown ZBPs much smaller than 2e2/h, with a recent observation of a peak-height close to 2e2/h. Here, we report a quantized conductance plateau at 2e2/h in the zero-bias conductance measured in InSb semiconductor nanowires covered with an Al superconducting shell. Our ZBP-height remains constant despite changing parameters such as the magnetic field and tunnel coupling, i.e. a quantized conductance plateau. We distinguish this quantized Majorana peak from possible non-Majorana origins, by investigating its robustness on electric and magnetic fields as well as its temperature dependence. The observation of a quantized conductance plateau strongly supports the existence of non-Abelian Majorana zero-modes in the system, consequently paving the way for future braiding experiments.Comment: 5 figure

Electric field tunable superconductor-semiconductor coupling in Majorana nanowires

We study the effect of external electric fields on superconductor-semiconductor coupling by measuring the electron transport in InSb semiconductor nanowires coupled to an epitaxially grown Al superconductor. We find that the gate voltage induced electric fields can greatly modify the coupling strength, which has consequences for the proximity induced superconducting gap, effective g-factor, and spin-orbit coupling, which all play a key role in understanding Majorana physics. We further show that level repulsion due to spin-orbit coupling in a finite size system can lead to seemingly stable zero bias conductance peaks, which mimic the behavior of Majorana zero modes. Our results improve the understanding of realistic Majorana nanowire systems.Comment: 10 pages, 5 figures, supplemental information as ancillary fil

Einfluss der Nutzung der Insertionshilfe bei der Implantation der MidScala-Elektrode auf das histologisch und radiologisch bewertete Trauma

Einleitung: Mit dem Ziel möglichst strukturerhaltender Cochlea Implantation wurden freie, nicht vorgeformte Elektrodenträger klinisch eingeführt. Auch die MidScala(MS)-Elektrode (Advanced Bionics) wurde unter diesem Gesichtspunkt entwickelt, wobei eine midskaläre Lage erreicht werden soll. Die Insertion kann mit einer Einführhilfe oder über Retraktion des Stiletts während der Insertion erfolgen. Ziel der Studie ist es zu untersuchen, ob die Nutzung der Insertionshilfe Einfluss auf den cochleären Strukturerhalt hat.Methode: Acht humane Felsenbeine (FB) wurden mit der MS-Elektrode implantiert, vier Präparate mit und vier ohne Insertionshilfe. Die Insertion erfolgte videodokumentiert durch einen erfahrenen CI-Chirurgen mit Erfassung der Insertionszeit. Nach Einbettung der Präparate folgte die radiologische Diagnostik mittels Digitaler Volumentomografie gefolgt von histologischer Aufarbeitung und Auswertung nach dem Eshragi Traumascale.Ergebnis: In allen Fällen gelang eine volle Insertion. Mit Insertionshilfe kam es in einem Fall zur Anhebung der Basilarmembran (BM) und zu einer Fehllage, ohne zu Anhebungen der BM in zwei FB. Die durchschnittliche Insertionszeit mit Einführhilfe (69,75s) wich von der Insertion ohne Hilfe (172,75s) ab. In dem Präparat mit der kürzesten Insertionszeit (47s) kam es zum Skalenwechsel unter Verwendung der Insertionshilfe.Diskussion: Beide Insertionsmethoden scheinen intracochleären Strukturerhalt zu ermöglichen. Die Nutzung der Insertionshilfe scheint über eine Reduktion der Insertionszeit ein höheres intracochleäres Trauma zu bedingen. Die Ergebnisse geben einen Hinweis darauf, dass insbesondere bei der Verwendung der Insertionshilfe auf eine langsame Insertionsgeschwindigkeit zu achten ist, um eine atraumatische Insertion zu gewährleisten.Unterstützt durch: Advanced Bionics GmbHDer Erstautor weist auf folgenden Interessenkonflikt hin: Mit freundlicher Unterstützung durch die Advanced Bionics Gmb