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

TL;DR

This study uses advanced Andreev reflection spectroscopy to investigate CuxBi2Se3, revealing the absence of zero-energy surface bound states and challenging the notion of Majorana fermions in this material.

Contribution

It introduces a nanoscale AR spectroscopy method and demonstrates that zero-bias conductance peaks are not intrinsic, questioning the topological superconductor nature of CuxBi2Se3.

Findings

Zero-bias conductance peaks depend on barrier strength.

Absence of zero-energy states suggests no Majorana fermions.

Reevaluation needed of CuxBi2Se3's superconducting properties.

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.