Giant Impurity Effects on Charge Loop Current Order States in Kagome Metals

Abstract

The exotic electronic states in the charge loop current (cLC) phase, in which the permanent charge current breaks the time-reversal symmetry, have been attracting increasing attention in recently discovered kagome metals AV3Sb5 (A = Cs, Rb, K). Interestingly, the cLC state is sensitively controlled by applying a small magnetic field as well as a tiny uniaxial strain. In addition, many experiments indicate that the cLC state is sensitive to the small number of impurities. To understand the impurity effects on the cLC electronic states accurately, we analyze the giant unit-cell (up to 1200 sites) kagome lattice model with single impurity potential. The loop current is found to be strongly suppressed within the current correlation length $ξ_J$ centered on the impurity site, where $ξ_J$ increases as the cLC order parameter $η$ decreases. (The cLC order is the pure imaginary hopping integral modulation $δt_{i,j}=\pm iη$.) In addition, both the uniform orbital magnetization $M_{orb}$ and the anomalous Hall conductivity $σ_{xy}$ are drastically suppressed by dilute impurities. Especially, the suppression ratio $R=-ΔM_{orb}/M_{orb}^0$ can exceed 50% with the introduction of 1% impurities. Unexpectedly, the ratio $R$ is qualitatively insensitive to $η$, in highly contrast to a naive expectation that $R$ is proportional to the current suppression area $πξ_J^2$. The resulting giant impurity effect of $M_{orb}$ would originates from the nonlocal contribution of the itinerant circulation of electrons. The present study gives a natural explanation of why the cLC electronic states in kagome metals are sensitive to dilute impurities.