Origin of switchable quasiparticle-interference chirality in loop-current phase of kagome metals measured by scanning-tunneling-microscopy

In the kagome superconductors AV₃Sb₅ (A=Cs,Rb,K), a cascade of correlated electron phases cause exotic symmetry-breaking quantum states. In particular, the dissipationless chiral loop-current phase has been attracting increasing attention. A crucial clue is offered by the chirality of the quasiparticle interference signal observed in scanning tunneling microscopy. However, the connection between loop-current chirality and quasiparticle interference chirality remains poorly understood. Here, we reveal theoretically that a pronounced chiral quasiparticle interference signal emerges in the extremely dilute impurity regime ( ≲ 0.1%). A single impurity at site Z induces a quasiparticle interference chirality χ_Z = ± 1, determined by the direction of the Z₃ nematicity, itself set by the relative position of the loop-current order in the star-of-David charge-density-wave phase. Notably, even a small magnetic field can smoothly switch the chirality, leading to field-induced shear lattice strain consistent with recent experiments. Our theoretical study provide key insights into the nature of the loop-current-induced symmetry-breaking states in kagome metals.