Zero-energy vortex bound state in the superconducting topological surface state of Fe(Se,Te) (1812.08995v2)

Abstract: Majorana quasiparticles (MQPs) in condensed matter play an important role in strategies for topological quantum computing but still remain elusive. Vortex cores of topological superconductors may accommodate MQPs that appear as the zero-energy vortex bound state (ZVBS). An iron-based superconductor Fe(Se,Te) possesses a superconducting topological surface state that has been investigated by scanning tunneling microscopies to detect the ZVBS. However, the results are still controversial. Here, we performed spectroscopic-imaging scanning tunneling microscopy with unprecedentedly high energy resolution to clarify the nature of the vortex bound states in Fe(Se,Te). We found the ZVBS at 0 $\pm$ 20 $\mu$eV suggesting its MQP origin, and revealed that some vortices host the ZVBS while others do not. The fraction of vortices hosting the ZVBS decreases with increasing magnetic field, while chemical and electronic quenched disorders are apparently unrelated to the ZVBS. These observations elucidate the conditions to achieve the ZVBS, and may lead to controlling MQPs.

• The paper demonstrates a zero-energy vortex bound state at 0±20 μeV, linking it to Majorana quasiparticles in Fe(Se,Te) superconductors.
• High-resolution SI-STM shows that the occurrence of ZVBS decreases with increasing magnetic field, highlighting vortex inhomogeneity.
• The findings indicate that chemical and electronic disorders do not affect ZVBS, emphasizing the role of vortex lattice arrangements.

Insights into Zero-Energy Vortex Bound States in Fe(Se,Te) Superconductors

The paper "Zero-energy vortex bound state in the superconducting topological surface state of Fe(Se,Te)" presents a comprehensive paper of the zero-energy vortex bound states (ZVBS) within the context of topological superconductors, particularly focusing on the iron-based superconductor Fe(Se,Te). The research aims to address the elusive nature of Majorana quasiparticles (MQPs) in condensed matter physics, which hold potential applications in topological quantum computing.

The authors utilize spectroscopic-imaging scanning tunneling microscopy (SI-STM) with high energy resolution to investigate the properties of vortex bound states in Fe(Se,Te). The paper reports the observation of ZVBS at 0±20 μeV in some vortices, which is indicative of their MQP origin. However, they note that not all vortices host the ZVBS, and the fraction decreases as the magnetic field strength increases. Interestingly, the observations suggest that chemical and electronic quenched disorders do not affect the presence of ZVBS.

The paper provides an in-depth analysis of the conditions necessary for the existence of ZVBS, which, in turn, could lead to methods for controlling MQPs. The authors emphasize that the conventional Caroli-de Gennes-Matricon (CdGM) states fail to account for the observed ZVBS, thereby highlighting a distinctive attribute of the MQPs.

Key Findings

1. MQP Identification in Vortices: The detection of ZVBS at an energy scale of 0±20 μeV suggests an association with MQPs, which aligns with theoretical predictions about the potential for intrinsic MQPs to exist in vortex cores.
2. Inhomogeneous ZVBS Distribution: The occurrence of ZVBS is found to be location-dependent within vortex cores. Approximately 80% of vortices exhibit ZVBS at lower magnetic fields (1 T), but this fraction diminishes with field intensity, specifically at 3 T. The observation underscores the influence of vortex interactions and the coherence of the lattice under varying magnetic fields.
3. Disorder Independence: The data indicate that chemical and electronic quenched disorders are not significant factors influencing the presence of ZVBS, leading to the hypothesis that vortex arrangement disorder might play a pivotal role instead.
4. Vortex Lattice and Magnetic Field Dependency: High-resolution SI-STM spectra reveal that the ZVBS probability decreases as magnetic field increases. The Fourier transform of the zero-energy conductance maps suggests losses in orientation correlation within the vortex lattice at higher magnetic fields.

Implications and Future Directions

The results obtained provide essential insights into the behaviors of vortices in superconducting topological surface states and offer plausible avenues towards understanding MQPs in such environments. The paper posits that in Fe(Se,Te), the manifestations of ZVBS not only depend on intrinsic properties but are also modulated by external magnetic influences and lattice arrangements.

This work suggests several future research directions:

• Theoretical Exploration of Vortex Disorder Impacts: Theoretical models could further elucidate the role of orientational disorder in determining ZVBS presence and stability.
• Magnetic Field Effects: Investigating the influence of varying magnetic field strengths on vortex arrangements and related phenomena like the Zeeman effect could offer deeper insights.
• Experimental Enhancements: Continued improvements in SI-STM technology and resolution might uncover further details about the MQPs in similar superconductors.

In conclusion, this paper contributes to the understanding of vortex physics and topological superconductivity, presenting a framework that may facilitate the manipulation and control of MQPs in quantum computing architectures. The findings emphasize the significance of understanding microscopic interactions in determining macroscopic quantum states, potentially guiding practical applications in quantum technologies.