Fermi-arc diversity on surface terminations of the magnetic Weyl semimetal Co3Sn2S2

Abstract: Bulk-surface correspondence in Weyl semimetals assures the formation of topological "Fermi-arc" surface bands whose existence is guaranteed by bulk Weyl nodes. By investigating three distinct surface terminations of the ferromagnetic semimetal Co3Sn2S2 we verify spectroscopically its classification as a time reversal symmetry broken Weyl semimetal. We show that the distinct surface potentials imposed by three different terminations modify the Fermi-arc contour and Weyl node connectivity. On the Sn surface we identify intra-Brillouin zone Weyl node connectivity of Fermi-arcs, while on Co termination the connectivity is across adjacent Brillouin zones. On the S surface Fermi-arcs overlap with non-topological bulk and surface states that ambiguate their connectivity and obscure their exact identification. By these we resolve the topologically protected electronic properties of a Weyl semimetal and its unprotected ones that can be manipulated and engineered.

• The paper demonstrates that surface termination dramatically alters Fermi-arc connectivity in Co3Sn2S2 via scanning tunneling spectroscopy.
• It employs ultra-high vacuum cleaving and ab initio calculations to map electronic structures with high precision.
• The findings suggest that engineered surface potentials can tune topological states, advancing spintronics and quantum computing applications.

Fermi-Arc Diversity and Connectivity in Magnetic Weyl Semimetals: Analyzing Surface Terminations of Co$_3$Sn$_2$S$_2$

Introduction

This paper examines the intriguing electronic properties of the ferromagnetic Weyl semimetal Co$_3$Sn$_2$S$_2$, focusing on the Fermi-arc surface bands manifesting due to bulk Weyl nodes. By investigating different surface terminations, this study provides empirical evidence for its classification as a time reversal symmetry broken Weyl semimetal. Importantly, the research highlights how surface potentials distinctly affect Fermi-arc contours and Weyl node connectivity, with implications for the understanding and engineering of topological states in these materials.

Methodology and Experimental Setup

The study employed scanning tunneling spectroscopy to visualize the structure and connectivity of Fermi-arcs across three terminations of Co$_3$Sn$_2$S$_2$: Sn, S, and Co. Each surface was cold cleaved under ultra-high vacuum conditions, ensuring pristine surface conditions crucial for accurate spectroscopic measurements. Ab initio calculations complemented the experimental observations, providing a reliable theoretical framework for interpreting the local surface band structures.

Surface Termination and Fermi-Arc Diversity

• Sn Termination: On the Sn-terminated surface, the intra-Brillouin zone connectivity of Fermi-arcs was observed, connecting Weyl nodes within the same zone. The QPI patterns and energy evolution presented a distinct manifestation of the magnetic Weyl semimetal phase, corroborated by clear interference patterns in the electronic states.
• S Termination: The S surface displayed significant overlap of Fermi-arcs with non-topological bulk and surface states, complicating the identification of connectivity. Despite this challenge, the analysis of QPI patterns revealed insights into energy deviations and quasi-nesting conditions around Weyl energies, underscoring the sensitivity of surface states to external perturbations.
• Co Termination: With Co termination, inter-Brillouin zone connectivity was noted, demonstrating Fermi-arcs traversing adjacent zones. The QPI results indicated distinct surface band structures with energy-dependent transformation of scattering modes, influenced by hybridization with surface states, a behavior less pronounced in other terminations.

Implications and Future Directions

The findings elucidate the critical role of surface termination in dictating the electronic topology of Weyl semimetals, specifically regarding the stability and connectivity of Fermi-arcs. The susceptibility of Fermi-arcs to local surface potentials opens avenues for manipulating these states through engineered surface perturbations, which could prove beneficial in applications exploiting topological transport phenomena.

The practical implication of these results lies in the potential to tailor surface electronic properties for advanced technological applications, including spintronics and quantum computing, where control over electron transport paths is crucial. Theoretically, the paper underscores the nuanced interplay between bulk and surface states in topological semimetals, challenging previously held assumptions about the rigidity of these properties and promoting further exploration into other candidate materials.

Conclusion

This research substantiates the classification of Co$_3$Sn$_2$S$_2$ as a magnetic Weyl semimetal and enriches the understanding of topological surface states by detailing variable Fermi-arc characteristics across different surface terminations. The study's comprehensive approach enables a deeper understanding of the interaction between surface modifications and topological features, paving the way for future explorations into the manipulation and control of Weyl semimetal properties.