[Paper Review] Distinctive momentum dependent charge-density-wave gap observed in CsV$_3$Sb$_5$ superconductor with topological Kagome lattice

Zhengguo Wang, Sheng Ma+15 more|arXiv (Cornell University)|Apr 12, 2021

Topological Materials and Phenomena20 references52 citations

TL;DR

The paper uses high-resolution ARPES on CsV3Sb5 to reveal a strongly momentum-dependent CDW gap, opening near M points while leaving states near Gamma largely gapless, suggesting a nesting-driven mechanism on a topological Kagome lattice.

ABSTRACT

CsV$_3$Sb$_5$ is a newly discovered Kagome superconductor that attracts great interest due to its topological nontrivial band structure and the coexistence of superconductivity and charge-density-wave (CDW) with many exotic properties. Here, we report the detailed characterization of the CDW gap in high-quality CsV$_3$Sb$_5$ single crystals using high-resolution angle-resolved photoemission spectroscopy. We find that the CDW gap is strongly momentum dependent. While gapped around the $M$ point, the electronic states remain gapless around the $Γ$ point and along the $Γ$-$K$ direction. Such momentum dependence indicates that the CDW is driven by the scattering of electrons between neighboring $M$ points, where the band structure hosts multiple saddle points and the density of state diverges near the Fermi level. Our observations of the partially gapped Fermi surface and strongly momentum-dependent CDW gap not only provide a foundation for uncovering the mechanism of CDW in CsV$_3$Sb$_5$, but also shed light on the understanding of how the CDW coexists with superconductivity in this topological Kagome superconductor.

Motivation & Objective

• Characterize the CDW gap structure in CsV3Sb5 single crystals.
• Determine momentum regions where the CDW gap opens or remains absent.
• Infer the CDW mechanism from the momentum-dependent gap distribution.
• Understand implications for CDW and superconductivity coexistence on a topological Kagome lattice.

Proposed method

• High-resolution angle-resolved photoemission spectroscopy (ARPES) on CsV3Sb5 single crystals.
• Map the electronic structure and CDW gap across the Brillouin zone.
• Identify momentum points with CDW gap opening and regions that remain gapless.
• Interpret the momentum dependence in terms of scattering between neighboring M points and DOS considerations.

Experimental results

Research questions

• RQ1 Where is the CDW gap opening in CsV3Sb5 and how does it vary with momentum?
• RQ2 Which regions of the Fermi surface remain gapless, and what does this imply about the CDW mechanism?
• RQ3 What does the momentum dependence reveal about the interaction processes driving CDW in a topological Kagome lattice?
• RQ4 How does the observed gap structure inform the coexistence of CDW with superconductivity?

Key findings

• CDW gap is strongly momentum dependent.
• The CDW gap is present around the M point but states remain gapless around Gamma and along Gamma–K.
• The momentum dependence suggests CDW is driven by scattering between neighboring M points with DOS divergence near the Fermi level.
• Observations show a partially gapped Fermi surface in CsV3Sb5.
• Results provide insight into the mechanism of CDW and its coexistence with superconductivity on a topological Kagome lattice.