Absence of zero-energy surface bound states in CuxBi2Se3 via a study of Andreev reflection spectroscopy

Abstract

CuxBi2Se3 has been proposed as a potential topological superconductor characterized by an odd-parity full bulk superconducting gap and zero-energy surface Andreev bound states (Majorana fermions). A consequence of such Majorana fermions is a peak in the zero-energy density of states which should lead to a persistent zero-bias-conductance-peak (ZBCP) in Andreev reflection (AR) or tunneling experiments. Here we employ a newly developed nanoscale AR spectroscopy method to study normal metal/superconductor (N-S) devices featuring CuxBi2Se3. The results show that a ZBCP can be tuned in or out from CuxBi2Se3 samples depending on the N-S barrier strength. While the appearance of ZBCP may be traced to different origins, its absence under finite barrier strength represents the absence of zero-energy Majorana fermions. The present observations thus call for a reexamination of the nature of the superconducting state in CuxBi2Se3.

18 pages, 5 figures, plus Supplementary Material (5 pages, 4 figures)

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• Superconducting proximity effect and Majorana fermions at the surface of a topological insulator
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• Local Measurements of the Superconducting Pairing Symmetry in CuxBi2Se3
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• Superconductivity in the doped topological insulator Cu${}_x$Bi${}_2$Se${}_3$ under high pressure
• Topological superfluids with time reversal symmetry
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