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

Title	Absence of evidence for chiral Majorana modes in quantum anomalous Hall-superconductor devices
Authors	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
Magazine	Science
Date	01/02/2020
DOI	10.1126/science.aax6361
Introduction	A quantum anomalous Hall (QAH) insulator, when coupled to an s-wave superconductor, is theorised to contain chiral Majorana modes. Recent experiments have interpreted a half-quantised two-terminal conductance plateau as evidence of these modes in a hybrid QAH-niobium device. However, such signatures can arise from non-Majorana mechanisms, particularly in disordered samples. This study investigates comparable hybrid devices with a well-regulated and transparent interface between the superconductor and QAH insulator. When in the QAH state with aligned magnetisation, the devices consistently exhibit half-quantised conductance. Our findings provide a detailed understanding of the superconducting proximity effect in QAH-superconductor hybrid devices, suggesting that the half-quantised conductance plateau is unlikely to be caused by chiral Majorana fermions in highly transparent interfaces.
Quote	Morteza Kayyalha, Di Xiao and Ruoxi Zhang et al. Absence of evidence for chiral Majorana modes in quantum anomalous Hall-superconductor devices. Science. 2020. Vol. 367(6473):64-67. DOI: 10.1126/science.aax6361
Materials	Semiconductors
Industry	Electronics