Twofold van Hove singularity and origin of charge order in topological kagome superconductor CsV3Sb5

Abstract: The layered vanadium antimonides AV3Sb5 (A = K, Rb, Cs) are a recently discovered family of topological kagome metals with a rich phenomenology of strongly correlated electronic phases including charge order and superconductivity. Understanding how the singularities inherent to the kagome electronic structure are linked to the observed many-body phases is a topic of great interest and relevance. Here, we combine angle-resolved photoemission spectroscopy and density functional theory to reveal multiple kagome-derived van Hove singularities (vHs) coexisting near the Fermi level of CsV3Sb5 and analyze their contribution to electronic symmetry breaking. Intriguingly, the vHs in CsV3Sb5 have two distinct flavors - p-type and m-type - which originate from their pure and mixed sublattice characters, respectively. This twofold vHs is unique property of the kagome lattice, and its flavor critically determines the pairing symmetry and ground states emerging in AV3Sb5 series. We establish that, among the multiple vHs in CsV3Sb5, the m-type vHs of the dxz/dyz kagome band and the p-type vHs of the dxy/dx2-y2 kagome band cross the Fermi level to set the stage for electronic symmetry breaking. The former band exhibits pronounced Fermi surface nesting, while the latter contributes via higher-order vHs. Our work reveals the essential role of kagome-derived vHs for the collective phenomena realized in the AV3Sb5 family, paving the way to a deeper understanding of strongly correlated topological kagome systems.

• The paper identifies two distinct van Hove singularities (p-type and m-type) in CsV3Sb5 near the Fermi level.
• The paper shows that m-type singularity facilitates Fermi surface nesting, triggering charge order, while p-type deviations influence superconducting behavior.
• The paper demonstrates that both interband and intraband couplings, alongside Berry curvature effects, underlie the material's topological and electronic properties.

Twofold van Hove Singularity and Charge Order in Kagome Superconductors: A Comprehensive Analysis

The paper under focus delivers an in-depth examination of the electronic properties of topological kagome superconductors, specifically CsV$_3$Sb$_5$. It investigates the contribution of van Hove singularities (vHs) present in the kagome lattice system to the observed charge order and superconductivity phenomena. Utilizing advanced techniques such as angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT), the authors have delineated the presence of two distinct types of vHs—dubbed p-type and m-type—each exhibiting unique properties and significantly impacting the material's many-body ground state.

Key Findings

1. Dual-Type vHs Characteristics: In CsV$_3$Sb$_5$, the intricate electronic structure features twofold vHs flavors. The p-type vHs, associated with d$_{xy}$/d$_{x^2-y^2}$ orbitals, and the m-type vHs, linked with d$_{xz}$/d$_{yz}$ orbitals, emerge near the Fermi level. This diversity in vHs flavors offers a deeper understanding of electronic symmetry breaking mechanisms.
2. Fermi Surface Nesting and Higher-Order vHs: Evidence indicates that the m-type vHs contributes to Fermi surface nesting, which is a precursor to charge order formation. Meanwhile, the p-type vHs affects electronic properties through its higher-order nature, identified through deviations from the typical linear dispersion patterns often expected at vHs points.
3. Interband and Intraband Contributions: The authors demonstrate that both inter- and intraband couplings play critical roles in the material's emergent properties. The presence of multiple Dirac points and the ensuing Berry curvature effects are highlighted, tying the topological aspects of the kagome lattice to its superconducting behavior.

Implications and Future Directions

The findings present a compelling case for the role of kagome lattice-derived vHs in facilitating novel phenomena in correlated electron systems. This tight coupling between the unique lattice structure and electronic properties suggests that other kagome-lattice-based materials might harbor similarly complex interactions that could be harnessed for designing new electronic devices or materials with unconventional superconducting or charge-ordering properties.

Future investigations might focus on mapping these vHs in different members of the AV$_3$Sb$_5$ family (where A = K, Rb), exploring how external conditions such as pressure or magnetic fields further modulate their properties. Moreover, connections to exotic quasiparticles like Majorana fermions and potential applications in quantum computing devices remain a tantalizing prospect worth exploring.

In conclusion, this paper advances our understanding of kagome superconductors' complex electronic landscape and opens avenues for further research into their multifaceted properties, promising significant advancements in the study of strongly correlated topological systems.