Time-reversal symmetry-breaking phenomena in transport study of kagome superconductivity

Recent studies have found that all three materials within the vanadium-based kagome superconductors ($\mathit{\text{A}}$V${}_3$Sb${}_5$, $\mathit{\text{A}}$ = K, Cs, Rb) exhibit time-reversal symmetry-breaking behaviors in the superconducting states. Among the three, the Josephson junctions structured Nb/K${}_{1-x}$V${}_3$Sb${}_5$/Nb and RbV${}_3$Sb${}_5$ show magnetic hysteresis below the superconducting transition temperature. CsV${}_3$Sb${}_5$ exhibits a zero-field superconducting diode effect, meaning the magnitude of the positive and negative superconducting critical currents are different. We first discuss the similarities and differences among the three above-mentioned experiments. Then, we discuss the possible mechanisms responsible for the unconventional superconducting transport phenomena: such as a chiral superconducting order parameter, and chiral pair density waves arising from the intertwining of the chiral charge order with superconductivity.