Absence of ferromagnetic instability and weak spin-orbit coupling effect in AV$_3$Sb$_5$ (A = Cs, Rb, and K)

TL;DR

This study uses density functional theory to show that AV$_3$Sb$_5$ kagome metals are nonmagnetic with weak spin-orbit coupling effects, aligning with experimental observations and challenging prior theories about their magnetic properties.

Contribution

The paper demonstrates that magnetic properties depend on k-point mesh density and finds minimal spin-orbit coupling influence, providing a refined understanding of these materials' electronic structure.

Findings

Nonmagnetic phase with dense k-point mesh matches experimental data

Coarser k-point mesh induces ferromagnetic instability via Stoner criterion

Weak spin-orbit coupling causes only slight gap opening at Dirac points

Abstract

A family of V-based kagome metals AV$_3$Sb$_5$ (A = Cs, Rb, K) presents an intriguing platform for exploring the interplay of time-reversal symmetry breaking, nontrivial topological bands, and electron correlations, resulting in a range of exotic quantum states, including the anomalous Hall effect, unconventional charge density waves, and superconductivity. These features prompt critical questions regarding the roles of magnetism and spin-orbit coupling (SOC) in these systems. Our density functional theory (DFT) calculations demonstrate a notable sensitivity of the magnetic properties to the choice of $k$-point mesh used in Brillouin zone integrations. Specifically, we find that using a dense $k$-point mesh yields a nonmagnetic pristine phase characterized by paramagnetic susceptibility, consistent with the recently observed Pauli paramagnetic behavior in single crystalline samples at high temperatures. In contrast, a coarser $k$-point mesh significantly increases the density of states at the Fermi level, inducing a ferromagnetic instability that satisfies the Stoner criterion. Moreover, our results show that the effect of SOC on both the geometric and electronic structures is minimal, with only a slight gap opening at the Dirac points, indicating a weak SOC influence in these materials. Importantly, our DFT band structure calculations closely align with angle-resolved photoemission spectroscopy data, reinforcing the notion of weak electron correlations in these kagome metals. This refined understanding challenges recent theoretical assertions that the interplay of magnetism, SOC, and electron correlations is essential for determining the nature of charge density waves in AV$_3$Sb$_5$.