High-resolution studies of the Majorana atomic chain platform (1611.02707v1)

Abstract: Ordered assemblies of magnetic atoms on the surface of conventional superconductors can be used to engineer topological superconducting phases and realize Majorana fermion quasiparticles (MQPs) in a condensed matter setting. Recent experiments have shown that chains of Fe atoms on Pb generically have the required electronic characteristics to form a 1D topological superconductor and have revealed spatially resolved signatures of localized MQPs at the ends of such chains. Here we report higher resolution measurements of the same atomic chain system performed using a dilution refrigerator scanning tunneling microscope (STM). With significantly better energy resolution than previous studies, we show that the zero bias peak (ZBP) in Fe chains has no detectable splitting from hybridization with other states. The measurements also reveal that the ZBP exhibits a distinctive 'double eye' spatial pattern on nanometer length scales. Theoretically we show that this is a general consequence of STM measurements of MQPs with substantial spectral weight in the superconducting substrate, a conclusion further supported by measurements of Pb overlayers deposited on top of the Fe chains. Finally, we report experiments performed with superconducting tips in search of the particle-hole symmetric MQP signature expected in such measurements.

High-Resolution Studies of the Majorana Atomic Chain Platform

The research paper under consideration presents a detailed investigation of Majorana Quasiparticles (MQPs) within the context of one-dimensional iron (Fe) atomic chains placed atop a superconducting lead (Pb) substrate. This work is significant in the field of condensed matter physics, as it explores the engineering of topological superconductors and the observation of emergent quantum states that exhibit non-Abelian statistics—attributes promising for quantum computing applications.

Summary of Findings

The authors employed a dilution refrigerator scanning tunneling microscope (STM) to achieve unprecedented energy-resolution measurements of Fe chains on Pb. This allowed them to circumvent limitations inherent in earlier studies conducted at temperatures around 1 Kelvin by achieving operational temperatures near 20 millikelvin. One of the principal findings is the robust observation of a zero-bias peak (ZBP) at the ends of the Fe chains. Importantly, this ZBP remains unsplit and firmly embedded at zero energy, implying minimal hybridization with adjacent electronic states. Through both empirical data and theoretical modeling, a distinctive "double eye" spatial pattern was identified in the ZBP. This pattern was evidenced over nanometer scale regions and attributed to significant spectral weight carried by the Pb substrate beneath the Fe chains.

In addition to the experimental findings, theoretical simulations enhanced the understanding of the spectroscopic properties observed in the chains. The paper effectively linked this spatially resolved conductance pattern to inherent characteristics of MQPs influenced by the superconducting landscape.

Implications and Future Directions

The implications of this research are notable on both theoretical and practical fronts. Theoretical implications include the validation of models regarding the localization of MQPs and the feasibility of using atomic chains as platforms for topological superconductivity. Practically, the paper advances the potential for using MQPs in quantum computing, especially in the construction of fault-tolerant qubits. The findings may also herald new fabrication techniques for optimizing atomic chain structures, potentially leading to improved material systems with configurable superconducting phases.

Future research directions might include exploring alternative material combinations to enhance proximity-induced superconductivity and reduce the complexity of the in-gap states. Additionally, advancements in STM techniques could further resolve the intricate interactions at play in these low-dimensional systems.

In conclusion, this comprehensive paper provides robust support for the hypothesis of MQPs in atomic Fe chains on Pb, bolstering the theoretical framework underlying topological superconductivity and opening new pathways for applied quantum technology. Further exploration and refinement of this platform could play a pivotal role in the ongoing evolution of quantum computing methodologies.