A semiconducting nanowire core fully wrapped by a superconducting shell has been proposed as an alternative geometry for obtaining Majorana modes without the need of fine tuning the chemical potential or an external magnetic field. While this robustness seems to avoid interpretation ambiguities in terms of non-topological Andreev bound states, we here demonstrate that the appearance of subgap states is actually governed by the junction region in tunneling spectroscopy measurements, not the full-shell nanowire itself. Short tunneling regions never show subgap states, while longer junctions always do. This can be understood in terms of quantum dots forming in the junction and hosting Andreev levels in the Yu-Shiba-Rusinov regime. Their intricate magnetic-field dependence, both through the Zeeman and the Little-Parks effects, may result in robust zero-bias peaks, a feature that could be easily misinterpreted as originating from Majoranas, but is unrelated to topology.
The authors thank A. Higginbotham, E. J. H. Lee and F. R. Martins for helpful discussions. This research was supported by the Scientific Service Units of IST Austria through resources provided by the MIBA Machine Shop and the nanofabrication facility; the NOMIS Foundation and Microsoft; the European Union’s Horizon 2020 research and innovation program under the Marie SklodowskaCurie grant agreement No 844511; the FETOPEN Grant Agreement No. 828948; the European Research Commission through the grant agreement HEMs-DAM No 716655; the Spanish Ministry of Science and Innovation through Grants PGC2018-097018-B-I00, PCI2018-093026, FIS2016-80434-P (AEI/FEDER, EU), RYC2011-09345 (Ram´on y Cajal Programme), and the Mar´ıa de Maeztu Programme for Units of Excellence in R&D (CEX2018-000805-M); the CSIC Research Platform on Quantum Technologies PTI-001.
Valentini M, Peñaranda F, Hofmann AC, et al. Non-topological zero bias peaks in full-shell nanowires induced by flux tunable Andreev states. arXiv.
Valentini, M., Peñaranda, F., Hofmann, A. C., Brauns, M., Hauschild, R., Krogstrup, P., … Katsaros, G. (n.d.). Non-topological zero bias peaks in full-shell nanowires induced by flux tunable Andreev states. arXiv.
Valentini, Marco, Fernando Peñaranda, Andrea C Hofmann, Matthias Brauns, Robert Hauschild, Peter Krogstrup, Pablo San-Jose Pablo San-Jose, Elsa Prada, Ramón Aguado, and Georgios Katsaros. “Non-Topological Zero Bias Peaks in Full-Shell Nanowires Induced by Flux Tunable Andreev States.” ArXiv, n.d.
M. Valentini et al., “Non-topological zero bias peaks in full-shell nanowires induced by flux tunable Andreev states,” arXiv. .
Valentini M, Peñaranda F, Hofmann AC, Brauns M, Hauschild R, Krogstrup P, Pablo San-Jose PS-J, Prada E, Aguado R, Katsaros G. Non-topological zero bias peaks in full-shell nanowires induced by flux tunable Andreev states. arXiv, 2008.02348.
Valentini, Marco, et al. “Non-Topological Zero Bias Peaks in Full-Shell Nanowires Induced by Flux Tunable Andreev States.” ArXiv, 2008.02348.