CsV$_3$Sb$_5$: a $\mathbb{Z}_2$ topological kagome metal with a superconducting ground state (2011.06745v1)

Abstract: Recently discovered alongside its sister compounds KV$3$Sb$_5$ and RbV$_3$Sb$_5$, CsV$_3$Sb$_5$ crystallizes with an ideal kagome network of vanadium and antimonene layers separated by alkali metal ions. This work presents the electronic properties of CsV$_3$Sb$_5$, demonstrating bulk superconductivity in single crystals with a T${c} = 2.5$K. The normal state electronic structure is studied via angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT), which categorize CsV$_3$Sb$_5$ as a $\mathbb{Z}_2$ topological metal. Multiple protected Dirac crossings are predicted in close proximity to the Fermi level ($E_F$), and signatures of normal state correlation effects are also suggested by a high temperature charge density wave-like instability. The implications for the formation of unconventional superconductivity in this material are discussed.

• The paper establishes CsV3Sb5 as a Z2 topological metal with a superconducting ground state at 2.5 K through detailed ARPES and DFT analysis.
• The study reveals a layered kagome lattice with quasi-2D band behavior and multiple Dirac points near the Fermi level.
• It identifies competing electronic instabilities, suggesting possible charge density wave formation intertwined with unconventional superconductivity.

CsV$_3$Sb$_5$: A $\mathbb{Z}_2$ Topological Kagome Metal with Superconducting State

The paper investigates the electronic properties of the compound CsV$_3$Sb$_5$, set within the broader context of kagome metals. The paper underscores the formation of a superconducting ground state at a transition temperature $T_c = 2.5\,\text{K}$ and identifies CsV$_3$Sb$_5$ as a $\mathbb{Z}_2$ topological metal. Approval of this state stems from comprehensive analyses deploying angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT), which reveal a complex electronic structure characterized by multiple Dirac points and topologically protected surface states proximate to the Fermi level.

Structural and Electronic Characterization

CsV$_3$Sb$_5$ crystallizes in a layered structure featuring a kagome network of vanadium cations, separated by antimony layers and cesium ions, establishing a unique two-dimensional metal framework. The compound is part of a family including KV$_3$Sb$_5$ and RbV$_3$Sb$_5$, and shares with them its crystallization in the P6/mmm space group. A detailed paper of the electronic structure is conducted, with ARPES measurements indicating quasi-2D band behavior and DFT calculations corroborating observed Dirac crossings near the Fermi level.

Bulk Superconductivity and Electronic Instabilities

Experimentally, transport measurements indicate the onset of superconductivity at $2.5\,\text{K}$, with magnetization, heat capacity, and resistivity aligning to underscore bulk superconductivity. Additionally, an intriguing anomaly at $T^*=94\,\text{K}$ suggests an underlying electronic instability, potentially linked to charge density waves (CDW), inferred through diffraction techniques revealing superlattice formations.

Theoretical Implications

The paper situates CsV$_3$Sb$_5$ within the scope of theoretical models predicting nesting-driven superconductivity and competing electronic orderings on a kagome lattice. The presence of topologically nontrivial features is pivotal, as they propose the potential for unconventional superconductivity through enhanced nesting effects between saddle points, aligning with previous models extending from related hexagonal lattice structures like doped graphene.

Future Perspectives

Emerging as a two-dimensional kagome metal exhibiting superconductivity and nontrivial topology, CsV$_3$Sb$_5$ provides ample ground for further exploration of such states amidst exotic quasiparticles. This material could serve as a fertile testing ground for hypothesized phenomena such as chiral superconductivity and unconventional pairing states, potentially at the intersection of CDW and superconducting phases.

Overall, CsV$_3$Sb$_5$ exemplifies a promising candidate for studies probing the interconnection and competition among electronic instabilities, band topology, and superconductivity—domains that resonate significantly within condensed matter physics and material science.