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

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.

Chiral Majorana fermions in graphene from proximity-induced superconductivity

“…For the (usS) case we find four expressions (for each λ E ≷ 0) for zero-energy solutions, but we need only three to define the border of the topological regions in Eq. (16). The gap is closed by an indirect closing that happens simultaneously between one band in K and one in K such that E K/K = 0.…”

“…Therefore, the BdG Chern number cannot be directly connected to a quantized Hall conductance that is proportional to the number of edge states. In fact, the transport properties of samples with chiral Majorana fermions and their unique signatures are the subject of ongoing research [14][15][16].…”

“…Recently, another scheme that exploits the chiral motion along the edge of a topological superconductor to realize non-Abelian braid operations was proposed [13]. The experimental realization of a single chiral Majorana fermion in a magnetically doped topological insulator in proximity to a superconductor could not be uniquely demonstrated [14][15][16].…”

Quantum computing’s reproducibility crisis: Majorana fermions

“…In 2020, these observations came under scrutiny after replication experiments were conducted. Science published an experiment led by researchers at Pennsylvania State University in University Park contradicting the 2017 report 4 . My group reproduced patterns from the 2018 Nature study, but demonstrated that they need not originate from Majorana 5 .…”

Intrinsic magnetic topological insulators

“…Based on this proposal, He et al 63 claimed to realize Majorana chiral edge states characterized by an e 2 /2h conductance plateau in Cr-doped (Bi,Sb) 2 Te 3 thin films in proximity with an Nb superconductor, but the results are questionably extrinsic. [64][65][66][67] Therefore, it is important to obtain equivalent p + ip superconductors by using intrinsic magnetic topological system. Peng and Xu 68 proposed a realization of chiral Majorana states using a heterostructure comprising MBT and an s-wave superconductor.…”