Disorder robustness and protection of Majorana bound states in ferromagnetic chains on conventional superconductors

Awoga, Oladunjoye A.; Björnson, Kristofer; Black‐Schaffer, Annica M.

doi:10.1103/physrevb.95.184511

Cited by 27 publications

(18 citation statements)

References 54 publications

(66 reference statements)

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“…The width of the SC, L y , is varied in order to tune the influence of the SC on the NW [39][40][41][42]. We have verified that our results remain qualitatively unchanged for ∆ sc and Γ both being smaller (or even larger), as well as when ∆ sc (i) is calculated self-consistently [50][51][52][53][54]. Our results also do not depend on L x , L NW , junction length, provided L x , L NW are longer than the superconducting coherence length and the junction is short, see Supplementary Material (SM) for more information [55].…”

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confidence: 57%

Supercurrent Detection of Topologically Trivial Zero-Energy States in Nanowire Junctions

2019

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We report the emergence of zero-energy states in the trivial phase of a short nanowire junction with strong spin-orbit coupling and magnetic field, formed by strong coupling between the nanowire and two superconductors. The zero-energy states appear in the junction when the superconductors induce a large energy shift in the nanowire, such that the junction naturally forms a quantum dot, a process that is highly tunable by the superconductor width. Most importantly, we demonstrate that the zero-energy states produce a π-shift in the phase-biased supercurrent, which can be used as a simple tool for their unambiguous detection, ruling out any Majorana-like interpretation.

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confidence: 57%

Supercurrent Detection of Topologically Trivial Zero-Energy States in Nanowire Junctions

2019

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“…( 1) and carry out a partial diagonalization using the Arnoldi iteration method [62] to extract the low-energy spectrum. We have further verified that self-consistent calculations of the superconducting order parameter do not modify the results presented here [52,63]. The parameters we consider in the SC are t sc = 15meV and |∆ sc | = 0.1t sc , which is in the range of experimentally measured values for NbTiN [5].…”

Section: Model and Methodssupporting

confidence: 76%

Robust topological superconductivity in weakly coupled nanowire-superconductor hybrid structures

Awoga,

Cayao,

Black-Schaffer

2021

Preprint

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We investigate the role of the coupling between a spin-orbit coupled semiconductor nanowire and a conventional s-wave superconductor on the emergence of the topological superconducting phase with Majorana bound states in an applied magnetic field. We show that when the coupling is strong, the topological phase transition point is very sensitive to the size of the superconductor and in order to reach the topological phase a strong magnetic field is required, which can easily be detrimental for superconductivity. Moreover, the induced energy gap separating the Majorana bound states and other quasi-particles in the topological phase is substantially suppressed compared to the gap at zero field. In contrast, in the weak coupling regime, we find that the situation is essentially the opposite, with the topological phase emerging at much lower magnetic fields and a sizable induced energy gap in the topological phase, that can also be controlled by the chemical potential of the superconductor. Furthermore, we show that the weak coupling regime does not generally allow for the formation of topologically trivial zero-energy states at the wire end points, in stark contrast to the strong coupling regime where such states are found for a wide range of parameters. Our results thus put forward the weak coupling regime as a promising route to mitigate the most unwanted problems present in nanowires for realizing topological superconductivity and Majorana bound states.

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“…The behavior of I ( ) is approximately the same as without disorder. This reflects the robustness of the topological phase, and thus of MBSs, against fluctuations in the chemical potential [ 58 – 59 ]. Stronger disorder (dotted and dash-dot curves) reduce the maximum value of I ( ) although its general behavior is preserved.…”

Section: Resultsmentioning

confidence: 99%

Andreev spectrum and supercurrents in nanowire-based SNS junctions containing Majorana bound states

Cayao¹,

Black‐Schaffer²,

Prada³

et al. 2018

Beilstein J. Nanotechnol.

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Hybrid superconductor–semiconductor nanowires with Rashba spin–orbit coupling are arguably becoming the leading platform for the search of Majorana bound states (MBSs) in engineered topological superconductors. We perform a systematic numerical study of the low-energy Andreev spectrum and supercurrents in short and long superconductor–normal–superconductor junctions made of nanowires with strong Rashba spin–orbit coupling, where an external Zeeman field is applied perpendicular to the spin–orbit axis. In particular, we investigate the detailed evolution of the Andreev bound states from the trivial into the topological phase and their relation with the emergence of MBSs. Due to the finite length, the system hosts four MBSs, two at the inner part of the junction and two at the outer one. They hybridize and give rise to a finite energy splitting at a superconducting phase difference of π, a well-visible effect that can be traced back to the evolution of the energy spectrum with the Zeeman field: from the trivial phase with Andreev bound states into the topological phase with MBSs. Similarly, we carry out a detailed study of supercurrents for short and long junctions from the trivial to the topological phases. The supercurrent, calculated from the Andreev spectrum, is 2π-periodic in the trivial and topological phases. In the latter it exhibits a clear sawtooth profile at a phase difference of π when the energy splitting is negligible, signalling a strong dependence of current–phase curves on the length of the superconducting regions. Effects of temperature, scalar disorder and reduction of normal transmission on supercurrents are also discussed. Further, we identify the individual contribution of MBSs. In short junctions the MBSs determine the current–phase curves, while in long junctions the spectrum above the gap (quasi-continuum) introduces an important contribution.

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Disorder robustness and protection of Majorana bound states in ferromagnetic chains on conventional superconductors

Cited by 27 publications

References 54 publications

Supercurrent Detection of Topologically Trivial Zero-Energy States in Nanowire Junctions

Supercurrent Detection of Topologically Trivial Zero-Energy States in Nanowire Junctions

Robust topological superconductivity in weakly coupled nanowire-superconductor hybrid structures

Andreev spectrum and supercurrents in nanowire-based SNS junctions containing Majorana bound states

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