Probing Loop Currents and Collective Modes of Charge Density Waves in Kagome Materials with NV Centers

Recently, the unconventional charge density wave (CDW) order with loop currents has attracted considerable attention in the Kagome material family AV${}_3$Sb${}_5$ (A = K, Rb, Cs). However, experimental signatures of loop current order remain elusive. In this work, based on the mean-field free energy, we analyze the collective modes of unconventional CDW order in a Kagome lattice model. Furthermore, we point out that phase modes in the imaginary CDW (iCDW) order with loop current orders result in time-dependent stray fields. We thus propose using nitrogen-vacancy (NV) centers to detect these time-dependent stray fields, providing a potential experimental approach to identifying loop current order.