Absence of evidence for chiral Majorana modes in quantum anomalous Hall-superconductor devices

Morteza Kayyalha, Di Xiao, Ruoxi Zhang, Jaeho Shin, Jue Jiang, Fei Wang, Yi Fan Zhao, Run Xiao, Ling Zhang, Kajetan M. Fijalkowski, Pankaj Mandal, Martin Winnerlein, Charles Gould, Qi Li, Laurens W. Molenkamp, Moses H.W. Chan, Nitin Samarth, Cui Zu Chang

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Abstract

A quantum anomalous Hall (QAH) insulator coupled to an s-wave superconductor is predicted to harbor chiral Majorana modes. A recent experiment interprets the half-quantized two-terminal conductance plateau as evidence for these modes in a millimeter-size QAH-niobium hybrid device. However, non-Majorana mechanisms can also generate similar signatures, especially in disordered samples. Here, we studied similar hybrid devices with a well-controlled and transparent interface between the superconductor and the QAH insulator. When the devices are in the QAH state with well-aligned magnetization, the two-terminal conductance is always half-quantized. Our experiment provides a comprehensive understanding of the superconducting proximity effect observed in QAH-superconductor hybrid devices and shows that the half-quantized conductance plateau is unlikely to be induced by chiral Majorana fermions in samples with a highly transparent interface.

Original languageEnglish (US)
Pages (from-to)64-67
Number of pages4
JournalScience
Volume367
Issue number6473
DOIs
StatePublished - Jan 3 2020

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Kayyalha, M., Xiao, D., Zhang, R., Shin, J., Jiang, J., Wang, F., Zhao, Y. F., Xiao, R., Zhang, L., Fijalkowski, K. M., Mandal, P., Winnerlein, M., Gould, C., Li, Q., Molenkamp, L. W., Chan, M. H. W., Samarth, N., & Chang, C. Z. (2020). Absence of evidence for chiral Majorana modes in quantum anomalous Hall-superconductor devices. Science, 367(6473), 64-67. https://doi.org/10.1126/science.aax6361