Intertwined van-Hove Singularities as a Mechanism for Loop Current Order in Kagome Metals

TL;DR

This paper proposes a microscopic mechanism involving intertwined van-Hove singularities with different mirror symmetries that explains the emergence of loop current order in Kagome metals, aligning with experimental observations of time-reversal symmetry breaking.

Contribution

It introduces an effective model showing how coupling between multiple van-Hove singularities leads to loop current order coexisting with charge bond order in Kagome metals.

Findings

Coupling of van-Hove singularities with opposite mirror eigenvalues favors loop current order.

The mechanism explains experimental time-reversal symmetry breaking in AV3Sb5.

The model applies specifically to Kagome metals, providing a microscopic understanding.

Abstract

Recent experiments on Kagome metals AV$_3$Sb$_5$ (A=Cs,Rb,K) indicated spontaneous time-reversal symmetry breaking in the charge density wave state in the absence of static magnetization. The loop current order (LCO) is proposed as its cause, but a microscopic model explaining the emergence of LCO through electronic correlations has not been firmly established. We show that the coupling between van-Hove singularities (vHS) with distinct mirror symmetries is a key ingredient to generate LCO ground state. By constructing an effective model, we find that when multiple vHS with opposite mirror eigenvalues are close in energy, the nearest-neighbor electron repulsion favors a ground state with coexisting LCO and charge bond order. It is then demonstrated that this mechanism applies to the Kagome metals AV$_3$Sb$_5$. Our findings provide an intriguing mechanism of LCO and pave the way for a deeper understanding of complex quantum phenomena in Kagome systems.