Electron correlations in kagome metals $AV_3Sb_5$ (A= K, Rb, Cs)

TL;DR

This study addresses how electronic correlations, quantified by $U$, $V$, and $J$, evolve under pressure in the kagome metals AV3Sb5. Using a $d$-$dp$ model within constrained RPA, the authors map the static Coulomb interactions across 0–9 GPa and reveal a distinctive low-pressure electronic instability in CsV3Sb5 near $p \approx 0.2$ GPa, accompanied by discontinuities in $U$ and $V$ while $J$ remains constant. Extending the analysis to interlayer spacing as a virtual pressure uncovers abrupt increases in $U$ and $V$ tied to a reduced $U/V$ ratio, and a pressure-driven shift of a Sb-$p$ and V-$d$ hybrid van Hove singularity that suggests a Lifshitz transition linked to CDW and superconductivity in CsV3Sb5. The results provide a quantitative cRPA-based framework for understanding pressure-tuned CDW physics and the unusual double superconducting dome in CsV3Sb5, emphasizing the role of interlayer coupling and Fermi-surface topology in kagome metals.

Abstract

The investigation of electronic order-quantum phase interplay in kagome lattices commonly employs the extended Kagome-Hubbard model, where the critical parameters comprise on-site $(U)$ and intersite $(V)$ Coulomb interactions. In prototypical kagome metals \ch{AV3Sb5} (A = K, Rb, Cs), the geometrically frustrated quasi-2D architecture induces pressure-dependent complexity in vanadium d-electron correlations, necessitating systematic theoretical scrutiny. Utilizing the $d-dp$ model within constrained random phase approximation (cRPA), we quantified $U$, $V$, and Hund's coupling $J$ under hydrostatic pressure (0-9 GPa). While \ch{KV3Sb5} and \ch{RbV3Sb5} exhibit pressure-insensitive interaction parameters, \ch{CsV3Sb5} manifests anomalous discontinuities in $U$ and $V$ near $0.2$ GPa, suggesting a first-order electronic phase transition. This work establishes cRPA-derived interaction landscapes as critical predictors for pressure-tunable quantum phenomena in correlated kagome systems, offers a new insight into the understanding of the interplay between the CDW transition and the double superconductivity dome in \ch{CsV3Sb5} at low pressure.

Figures (10)

• Figure 1: Crystal structure of AV3Sb5. The dotted line indicates a unit cell, in which three atomic V sites are labeled by $A,B,C$.
• Figure 2: The orbital projected bands of CsV3Sb5. The V-$d$ dominant bands [(d)-(f)] exhibit characteristic flat-bands behavior of two-dimensional kagome lattice. Conversely, the Sb-$p$ dominant bands [(b)-(c)] display strong three-dimensional character, evidenced by significant band dispersion along $k_z$ direction. Comparing (b) and (e), the overlap of Sb-($p_x+p_y$) and V-($d_{xz}+d_{yz}$) orbitals is also noticeable.
• Figure 3: (a) Projected density of states of CsV3Sb5. (b) The lattice parameters of AV3Sb5 as function of pressure. The V-Sb layer distance decreases more aggressively upon increasing pressure due to the quasi-2D nature of AV3Sb5.
• Figure 4: The VHS (marked by a green circle) formed by Sb-($p_x+p_y$) and V-($d_{xz}+d_{yz}$) orbitals respond to pressure. With increasing pressure, the energy position of the VHS is moving toward higher energy.
• Figure 5: The evolution of (a) $U$, (b) $V$ and (c) $J$ as function of pressure respectively. (d)-(f) are the enlarged views of the low-pressure section.