Observation of topological superconductivity on the surface of an iron-based superconductor (1706.05163v2)

Abstract: Topological superconductors, whose edge hosts Majorana bound states or Majorana fermions that obey non-Abelian statistics, can be used for low-decoherence quantum computations. Most of the proposed topological superconductors are realized with spin-helical states through proximity effect to BCS superconductors. However, such approaches are difficult for further studies and applications because of the low transition temperatures and complicated hetero-structures. Here by using high-resolution spin-resolved and angle-resolved photoelectron spectroscopy, we discover that the iron-based superconductor FeTe1-xSex (x = 0.45, Tc = 14.5 K) hosts Dirac-cone type spin-helical surface states at Fermi level, which open an s-wave SC gap below Tc. Our study proves that the surface states of FeTe0.55Se0.45 are 2D topologically superconducting, and thus provides a simple and possibly high-Tc platform for realizing Majorana fermions.

• The paper confirms intrinsic topological superconductivity in FeTe₀.₅₅Se₀.₄₅ by directly observing Dirac-cone type surface states.
• It employs high-resolution spin- and angle-resolved photoelectron spectroscopy to verify spin-helical textures and measure the s-wave superconducting gap below the critical temperature.
• The findings simplify the realization of topologically superconducting states, paving the way for potential Majorana fermions and advances in quantum computing.

Topological Superconductivity in FeTe₀.₅₅Se₀.₄₅: Experimental Verification and Implications

The paper presents a comprehensive paper of the topological superconductivity manifested on the surface of the iron-based superconductor FeTe₀.₅₅Se₀.₄₅, achieved through a high-resolution spin-resolved and angle-resolved photoelectron spectroscopy analysis. This research addresses the challenges associated with previously proposed topological superconductors, particularly those requiring proximity effects to BCS superconductors and complex heterostructures, by showcasing an alternative intrinsic mechanism for realizing topological superconductivity.

Key Experimental Observations and Findings

The primary objective of this paper was to confirm the existence of Dirac-cone type spin-helical surface states that open an s-wave superconducting (SC) gap below the critical temperature (Tc) in FeTe₀.₅₅Se₀.₄₅. The following critical observations were made:

1. Dirac-Cone Type Surface States: The researchers employed high-resolution angle-resolved photoelectron spectroscopy (ARPES) to detect Dirac-cone type surface states. These observations confirmed the non-trivial topological nature of the surface states predicted by theoretical calculations.
2. Spin-Helical Texture: Spin-resolved ARPES experiments verified the spin-polarized nature of the Dirac-cone surface states, characteristic of a spin-helical texture. The reversed spin polarizations at different Fermi surface positions corroborated theoretical predictions of spin-momentum locking.
3. s-Wave Superconducting Gap: The paper demonstrated the formation of an s-wave superconducting gap at the surface states, consistent with BCS theory. The gap's magnitude and its evolution as a function of temperature were measured, confirming superconducting behavior in these states.

The intrinsic topological superconductor nature of FeTe₀.₅₅Se₀.₄₅ is pivotal as it simplifies the realization of superconducting states with topological properties without the need for complicated heterostructures.

Implications and Future Directions

The confirmation of topologically superconducting states in FeTe₀.₅₅Se₀.₄₅ opens several new avenues for research and technology development:

• Majorana Fermions and Quantum Computing: The intrinsic topological surface states facilitate the creation of Majorana bound states at magnetic vortices, observable in scanning tunneling microscopy (STM) experiments. These states are potential candidates for low-decoherence quantum computation, offering a path towards robust quantum systems due to their non-Abelian statistical properties.
• Higher Temperature Applications: The material's capability to achieve higher Tc under specific conditions provides a promising platform for developing practical applications of topological superconductivity. This is critical for the integration of superconducting materials into current technological systems.
• Exploration of New Topological Materials: The approach delineated in this paper might prompt the discovery and synthesis of novel classes of materials that possess similar topological properties and superconductivity.

From a theoretical standpoint, this research calls for further exploration of the interplay between spin-orbit coupling and superconductivity in other iron-based systems. Additionally, the potential scaling and integration of FeTe₀.₅₅Se₀.₄₅ in quantum devices spur optimism for advancing topological quantum computing, necessitating further experimental studies to explore its utility in viable quantum computational frameworks.