Nearly quantized conductance plateau of vortex zero mode in an iron-based superconductor (1904.06124v2)

Abstract: Majorana zero-modes (MZMs) are spatially-localized zero-energy fractional quasiparticles with non-Abelian braiding statistics that hold a great promise for topological quantum computing. Due to its particle-antiparticle equivalence, an MZM exhibits robust resonant Andreev reflection and 2e2/h quantized conductance at low temperature. By utilizing variable-tunnel-coupled scanning tunneling spectroscopy, we study tunneling conductance of vortex bound states on FeTe0.55Se0.45 superconductors. We report observations of conductance plateaus as a function of tunnel coupling for zero-energy vortex bound states with values close to or even reaching the 2e2/h quantum conductance. In contrast, no such plateau behaviors were observed on either finite energy Caroli-de Genne-Matricon bound states or in the continuum of electronic states outside the superconducting gap. This unique behavior of the zero-mode conductance reaching a plateau strongly supports the existence of MZMs in this iron-based superconductor, which serves as a promising single-material platform for Majorana braiding at a relatively high temperature.

Nearly Quantized Conductance Plateau of Vortex Zero Mode in an Iron-Based Superconductor

The paper of Majorana zero modes (MZMs) is an intriguing aspect of condensed matter physics, primarily due to their potential applications in topological quantum computing. The paper "Nearly Quantized Conductance Plateau of Vortex Zero Mode in an Iron-Based Superconductor" examines the presence of MZMs in an iron-based superconductor, specifically FeTeSe, using scanning tunneling spectroscopy (STS) and reveals critical insights into their transport properties.

The authors investigate vortex zero modes in FeTeSe and report a nearly quantized conductance plateau that suggests the existence of MZMs at zero energy. This is achieved through variable-tunnel-coupled STS, allowing for detailed examination of the tunneling conductance as a function of tunnel coupling. The results show conductance plateaus close to, or reaching, the universal value of $2e^2/h$ in zero-energy vortex bound states, consistent with the predicted resonant Andreev reflection from MZMs.

This research highlights three main findings:

1. Tunneling Conductance Insights: The paper finds that the zero-bias conductance plateau is nearly quantized and does not vary significantly with the tunnel coupling, a behavior indicative of resonant Andreev reflection facilitated by MZMs. In contrast, finite-energy Caroli-de Gennes-Matricon bound states and other trivial sub-gap states exhibit a lack of plateau behavior, further substantiating the unique signature of MZMs.
2. Experimental Evidence and Methodology: With an effective temperature of 377 mK and utilizing high-precision STS, the research presents a thorough experimental setup and data acquisition method to rule out alternative explanations such as instrument broadening or quantum ballistic transport. This methodological rigor enhances the reliability of the observed quantization behavior.
3. Statistical Analysis of Conductance Plateaus: The authors present a comprehensive statistical analysis over 60 vortex measurements, discovering that more than 50% of the vortices showed a conductance plateau, with values clustered between 40% to 60% of the expected quantized value.

The implications of these findings are significant for both practical applications and theoretical advancements in the domain of topological quantum computing. The nearly quantized conductance plateau potentially serves as a reliable signature for MZMs in iron-based superconductors, thus positioning FeTeSe as a promising material platform for realizing topological quantum computation processes like Majorana braiding. Moreover, the paper adds a robust experimental dimension to the theoretical models of MZMs, providing a pathway for future research into unambiguous detection and manipulation of Majorana modes.

The paper also addresses some inherent challenges, such as the potential impact of quasiparticle poisoning and instrumental broadening on the precision of the measurements, suggesting further refinements in experimental technique could be necessary.

Looking forward, this paper paves the way for more sophisticated experiments involving MZMs and could inspire future research into exploiting these quasiparticles for fault-tolerant quantum computation. The iron-based FeTeSe, as a single material platform with significant adaptability, might provide essential breakthroughs in the practical realization of quantum computation systems. The continued exploration of MZM properties and their interaction with superconducting states could enhance our understanding of topological phases, potentially leading to innovations in quantum device engineering.