Loop Current Order on the Kagome Lattice

TL;DR

This paper models loop current order (LCO) on the kagome lattice, revealing its emergence as a ground state and its connection to quantum anomalous Hall states, with implications for kagome materials.

Contribution

Develops a microscopic model for LCO on the kagome lattice using unbiased functional renormalization group calculations, identifying conditions for its emergence.

Findings

LCO emerges as the many-body ground state at Van Hove filling.

Sublattice interference suppresses onsite charge density wave order.

LCO state resembles the Haldane model and leads to a quantum anomalous Hall state.

Abstract

Recent discoveries in kagome materials have unveiled their capacity to harbor exotic quantum states, including intriguing charge density wave (CDW) and superconductivity. Notably, accumulating experimental evidence suggests time-reversal symmetry breaking within the CDW, hinting at the long-pursued loop current order (LCO). Despite extensive research efforts, achieving its model realization and understanding the mechanism through unbiased many-body simulations have remained both elusive and challenging. In this Letter, we develop a microscopic model for LCO on the spinless kagome lattice with nonlocal interactions, utilizing unbiased functional renormalization group calculations to explore ordering tendencies across all two-particle scattering channels. At the Van Hove filling, we identify sublattice interference to suppress onsite CDW order, leaving LCO, charge bond order, and nematic CDW state as the main competitors. Remarkably, a $2\times2$ LCO emerges as the many-body ground state over a significant parameter space with strong second nearest-neighbor repulsion, stemming from the unique interplay between sublattice characters and lattice geometry. The resulting electronic model with LCO bears similarities to the Haldane model and culminates in a quantum anomalous Hall state. We also discuss potential experimental implications for kagome metals.