Mechanism of Loop Current Order in Kagome metals AV₃Sb₅

Kagome superconductor AV₃Sb₅ (A=K, Cs, Rb) exhibits rich quantum phase transitions, such as bond-order (BO), time-reversal-symmetry-breaking (TRSB) phase.

TRSB was reported by μSR, Kerr rotation, field-tuned chiral transport and STM study. More recently, magnetic torque measurement reveals the nematic order with TRSB at 130 [K].



However, the microscopic origin of TRSB and C₂-nematicity have been unsolved. To solve this problem, we consider the important roles of bond-order (BO) fluctuations, which is developed near the quantum-critical point of BO phase. Considering the exchange processes of BO fluctuation, we reveal that the chiral current phase is the most stable phase. This exchange process cause the sizable off-site Umklapp scattering. The order parameter of loop current is expressed by the imaginary hopping in Hermite Hamiltonian. Thus, the chiral current order brings TRSB. Furthermore, we discover that the coexistence of the BO and current order cause the novel C₂-nematicity along the three lattice directions (3Q) on kagome lattice. To show this fact, we calculate the Ginzburg-Landau coefficients and find the emergence of C₂-nematic state. The present theory reveals the close relationship between the TRSB, BO, C₂-nematicity.