Chiral topological superconductivity in hole-doped Sn/Si(111)

A third monolayer of tin atoms on the semiconductor substrate Si(111) has been shown to become superconducting upon six to ten percent hole doping. Experiments have reported promising results hinting at a superconducting chiral $d$-wave order parameter. Here we examine Sn/Si(111) by combining most recent ab initio results, quasi-particle interference calculations, state-of-the-art truncated-unity functional renormalization group simulations and Bogoliubov-de Gennes analysis. We show remarkable agreement between experimental and theoretical quasi-particle interference data both in the metallic and superconducting regimes. The interacting phase diagram reveals that the superconductivity is indeed chiral $d$-wave with Chern number $C=4$. Surprisingly, magnetically ordered phases are absent, instead we find charge density wave order, as observed in related compounds, as a competing phase. Our results demonstrate that Sn/Si(111) is an outstanding candidate material for chiral topological superconductivity.

💡 Research Summary

The research paper, “Chiral topological superconductivity in hole-doped Sn/Si(111),” presents a rigorous theoretical investigation into the emergence of chiral topological superconductivity within a specific atomic-scale interface. The study focuses on the third monolayer of tin (Sn) grown on a silicon (Si(111)) substrate, specifically examining the regime where the system undergoes 6% to 10% hole doping.

To provide a definitive characterization of the superconducting state, the authors employed a sophisticated multi-methodological approach. They integrated state-of-the-art ab initio calculations with quasi-particle interference (QPI) simulations to bridge the gap between theoretical predictions and experimental observations. A key strength of this work lies in the remarkable agreement between the calculated QPI patterns and experimental data, which holds true in both the metallic and superconducting regimes. This alignment validates the underlying electronic structure models used in the study.

Furthermore, the researchers utilized the truncated-unity functional renormalization group (fRG) method to construct an interacting phase diagram. This allowed them to identify the precise nature of the superconducting order parameter. The study confirms that the superconductivity in Sn/Si(111) possesses chiral d-wave symmetry, characterized by a significant Chern number of $C=4$. Such a high Chern number is a critical finding, as it indicates a robust topological nature that could potentially host protected edge states, making the material an exceptional candidate for topological quantum computing applications.

A particularly intriguing finding of this research is the nature of the competing phases within the system. In many strongly correlated superconducting materials, magnetic ordering often competes with and suppresses superconductivity. However, in the Sn/Si(111) system, the authors found that magnetically ordered phases are entirely absent. Instead, they identified Charge Density Wave (CDW) order as the primary competing phase. This distinction provides profound insight into the unique electronic correlations present in this interface, suggesting that the physics is driven by charge-density fluctuations rather than spin-based interactions.

In conclusion, the study establishes Sn/Si(111) as a premier platform for exploring chiral topological superconductivity. By demonstrating the stability of the $C=4$ chiral d-wave state and identifying the role of CDW competition, the authors have provided a roadmap for future experimental and technological developments in the field of topological quantum electronics.