Magnetic field independent sub-gap states in hybrid Rashba nanowires

Most reports on the highly visible topic of Majorana Fermions in solid state systems are based on the observation of magnetic field independent transport resonances at zero bias, so-called zero-bias peaks. Such topologically non-trivial states can form if a conventional superconductor is coupled to a material with a strong spin-orbit interaction.

In the work, published in Physical Review Letters, the team around Dr. Christian Jünger found that in such systems, magnetic field independent states can also form in the topologically trivial phase, either at zero bias, or at a finite bias, because the injected electron spins are rotated by the spin orbit interaction in such a way, that the effect of an external magnetic field is averaged out over the finite length of the nanowire. As a byproduct, this also gives the opportunity to extract the badly established spin-orbit strength in such materials. The finding that not only Majorana bound states can be immune to magnetic fields is crucial for future interpretation of magnetic field measurements of superconducting bound states in general.

The article was highlighted by the editorial board as PRL Editors’ Suggestion as an outstanding publication.

Christian Jünger et al. Phys. Rev. Lett. 125, 017701 (2020)

Up left:  SEM image of the investigated device, showing an zincblende InAs nanowire with an integrated QD (red) between two wurtzite tunnel barriers (green), located l_LS ≈ 220 nm from the superconducting (SC) electrode (scale bar: 100 nm). Up right: schematic illustration of the case that the spin orbit length equals the length of the nanowire lead segment l_LS = l_so (“commensurate case”), resulting in effective magnetic moment of m_eff = 0. Bottom: Magnetic field independent subgap states (red dashed lines) in conductance map (left) and waterfol plot (right).





Paper out: Immune to Magnetic fields