Lawrence Berkeley National Laboratory

Spontaneous symmetry breaking in kagome metals remains highly debated, especially with respect to the presence of time-reversal symmetry breaking and the temperature range over which it develops. A loop-current order, characterized by complex phases in intersite hopping, has been proposed as the mechanism responsible for the breaking of time-reversal symmetry, although it has not yet been confirmed experimentally. Here we present evidence that time-reversal symmetry is broken well above the temperature at which the charge density wave order develops in the kagome metal CsV3Sb5. Using momentum-resolved and domain-selective measurements of circular dichroism in photoemission intensity, we observe dichroic signal that originates from the time-reversal symmetry broken state. This finding also points to the presence of loop-current order. The temperature dependence of the dichroic response shows a complex evolution, revealing how loop-current order is intertwined with the charge ordered state. Our results, therefore, not only support the existence of loop-current order in this compound but also highlight a hierarchy of phase transitions—from loop-current order to charge density wave order and ultimately to superconductivity. These insights deepen our understanding of the phase landscape in kagome metals and highlight connections with a correlated system exhibiting analogous transition hierarchy.