Majorana zero-modes-a type of localized quasiparticle-hold great promise for topological quantum computing. Tunnelling spectroscopy in electrical transport is the primary tool for identifying the presence of Majorana zero-modes, for instance as a zero-bias peak in differential conductance. The height of the Majorana zero-bias peak is predicted to be quantized at the universal conductance value of 2e/h at zero temperature (where e is the charge of an electron and h is the Planck constant), as a direct consequence of the famous Majorana symmetry in which a particle is its own antiparticle. The Majorana symmetry protects the quantization against disorder, interactions and variations in the tunnel coupling. Previous experiments, however, have mostly shown zero-bias peaks much smaller than 2e/h, with a recent observation of a peak height close to 2e/h. Here we report a quantized conductance plateau at 2e/h in the zero-bias conductance measured in indium antimonide semiconductor nanowires covered with an aluminium superconducting shell. The height of our zero-bias peak remains constant despite changing parameters such as the magnetic field and tunnel coupling, indicating that it is a quantized conductance plateau. We distinguish this quantized Majorana peak from possible non-Majorana origins by investigating its robustness to electric and magnetic fields as well as its temperature dependence. The observation of a quantized conductance plateau strongly supports the existence of Majorana zero-modes in the system, consequently paving the way for future braiding experiments that could lead to topological quantum computing.

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. gate induced electric fields. Due to the change in coupling, the renormalization of material parameters is altered, as evidenced by a change in the effective g-factor of the hybrid system. Furthermore, the electric field is shown to affect the spin-orbit interaction, revealed by a change in the level repulsion between Andreev states. Our experimental findings are corroborated by numerical simulations. Experimental set-upWe have performed tunneling spectroscopy experiments on four InSb-Al hybrid nanowire devices, labeled A-D, all showing consistent behavior. The nanowire growth procedure is described in [20]. A scanning electron micrograph (SEM) of device A is shown in figure 1(a). Figure 1(b) shows a schematic of this device and the measurement set-up. For clarity, the wrap-around tunnel gate, tunnel gate dielectric and contacts have been removed on one side. A normal-superconductor (NS) junction is formed between the part of the nanowire covered by a thin shell of aluminum (10 nm thick, indicated in green, S), and the Cr /Au contact (yellow, N). The transmission of the junction is controlled by applying a voltage V Tunnel to the tunnel gate (red), galvanically isolated from the nanowire by 35 nm of sputtered SiN x dielectric. The electric field is induced by a global back gate voltage V BG , except in the case of device B, where this role is played by the side gate voltage V SG . Further details on device fabrication and design are included in appendices A and B. To obtain information about the density of states (DOS) in the proximitized nanowire, we measure the differential conductance dI/dV Bias as a function of applied bias voltage V Bias . In the following, we will label this quantity as dI/dV for brevity. A magnetic field is applied along the nanowire direction (x-axis in figures 1(b), (c)). All measurements are performed in a dilution refrigerator with a base temperature of 20 mK. Theoretical modelThe device geometry used in the simulation is shown in figure 1(c). We consider a nanowire oriented along the x-direction, with a hexagonal cross-section in the yz-plane. The hybrid superconductor-nanowire system is described by the Bogoliubov-de Gennes (BdG) Hamiltonian

While understanding translocation of DNA through a solid-state nanopore is vital for exploiting its potential for sensing and sequencing at the single-molecule level, surprisingly little is known about the dynamics of the propagation of DNA through the nanopore. Here we use linear double-stranded DNA molecules, assembled by the DNA origami technique, with markers at known positions in order to determine for the first time the local velocity of different segments along the length of the molecule. We observe large intramolecular velocity fluctuations, likely related to changes in the drag force as the DNA blob unfolds. Furthermore, we observe an increase in the local translocation velocity toward the end of the translocation process, consistent with a speeding up due to unfolding of the last part of the DNA blob. We use the velocity profile to estimate the uncertainty in determining the position of a feature along the DNA given its temporal location and demonstrate the error introduced by assuming a constant translocation velocity.