Chiral flux phase in the Kagome superconductor AV$_3$Sb$_5$ (2103.07097v2)

Abstract: We argue that the topological charge density wave phase in the quasi-2D Kagome superconductor AV$_3$Sb$_5$ is a chiral flux phase. Considering the symmetry of the Kagome lattice, we show that the chiral flux phase has the lowest energy among those states which exhibit $2\times2$ charge orders observed experimentally. This state breaks the time-reversal symmetry and displays anomalous Hall effect. The explicit pattern of the density of this state in real space is calculated. These results are supported by recent experiments and suggest that these materials are a new platform to investigate the interplay between topology, superconductivity and electron-electron correlations.

• The paper identifies the chiral flux phase as an energetically favorable 2×2 CDW state that explains the anomalous Hall effect and time-reversal symmetry breaking.
• It employs symmetry and microscopic charge distribution analyses to reveal distinct orbital current patterns in the Kagome lattice.
• The study opens avenues for advanced theoretical models and experimental validations of topological superconductivity in correlated Kagome materials.

Insights into the Chiral Flux Phase in Kagome Superconductors AV$_3$Sb$_5$

The paper "Chiral flux phase in the Kagome superconductor AV$_3$Sb$_5$" investigates the intriguing phenomena associated with the topological charge density wave (CDW) phase in the quasi-2D Kagome superconductor AV$_3$Sb$_5$. The paper primarily focuses on understanding the chiral flux phase (CFP) as a viable explanation for the anomalous Hall effect and observed time-reversal symmetry breaking in these compounds.

Research Context and Motivation

Kagome lattice structures provide a fertile ground for exploring complex many-body correlation physics due to their unique electronic and geometric properties, such as Dirac cones and flat bands. The recent discovery of AV$_3$Sb$_5$ (A=K, Rb, Cs), characterized by a quasi-2D Kagome lattice, has added a new dimension to this exploration. These materials exhibit intriguing superconductivity alongside topological phenomena, spurred by an observed $2 \times 2$ charge density wave (CDW) order. While experimental data has suggested various features of this order, a comprehensive theoretical explanation has remained elusive until now.

Key Aspects of the Study

The authors propose that the CFP, a state with a $2 \times 2$ CDW configuration, serves as the most energetically favorable state that adheres to the symmetries of the Kagome lattice while providing a coherent framework to explain experimental observations:

• Symmetry and Energy Considerations: The paper outlines that CFP not only minimizes energy among candidate states but also respects the lattice symmetries, making it a highly plausible phase for the underlying CDW state.
• Time-Reversal Symmetry and Hall Response: The CFP breaks time-reversal symmetry (${T}$), leading to an intrinsic quantum anomalous Hall response. The calculated Hall conductance in the CFP scenario, though not quantized due to multi-orbital features, explains the experimentally observed anomalous Hall effect.
• Density of States and Charge Distribution: Detailed calculations demonstrate a distinct charge distribution pattern, differentiating between sites with anti-clockwise and clockwise current loops, offering a microscopic view in line with significant scanning tunneling microscopy (STM) observations.

Implications and Future Directions

This research provides crucial insights into the interplay between topology, electron-electron interactions, and superconductivity in Kagome superconductors:

1. Topological Superconductivity: The identification of the CFP could explain how such nontrivial chiral states potentially couple with the superconducting phase in AV$_3$Sb$_5$, suggesting avenues for topological superconductivity research.
2. Exotic Collective States: The CFP's similarity with loop-current and d-density wave states proposed for cuprates implies broader applications within correlated systems. This link warrants additional investigation using techniques such as polarized neutron diffraction to observe orbital magnetism associated with CFP.
3. Theoretical Developments: The paper calls for further theoretical modeling, possibly expanding on extended Hubbard or mean-field approaches, to capture nuances of electron interactions underpinning CFP. These models could extend to other Kagome-lattice-based materials.

In conclusion, this paper contributes a significant theoretical advancement in understanding Kagome superconductors, particularly elucidating the nature of CDW states in AV$_3$Sb$_5$. By providing comprehensive evidence for the existence and implications of the chiral flux phase, the paper sets the stage for renewed experimental and theoretical investigations into these complex systems. Further research could illuminate how these states influence superconducting behavior and explore their potential for realizing novel quantum devices.