Quantum metric–induced giant and reversible nonreciprocal transport phenomena in chiral loop-current phases of kagome metals

Emergence of quantum orders with nontrivial quantum geometric properties in metals represent central issues in condensed matter physics. In this context, recently discovered chiral loop-current order in kagome metals has garnered significant attention. Particularly noteworthy is the giant electrical magnetochiral anisotropy (eMChA) observed in CsV₃Sb₅, which provides compelling evidence for the simultaneous breaking of time-reversal and inversion symmetries. However, the origin of the eMChA and its fundamental connection to the loop-current remain highly elusive, as the loop-current itself preserves inversion symmetry. Here, we demonstrate that the loop-current phase breaks inversion symmetry in the presence of the experimentally observed stripe charge-density wave, leading to finite eMChA coefficient [Formula: see text]. In this mechanism, [Formula: see text] is proportional to the product of the loop-current-induced orbital magnetization, [Formula: see text], and the lifetime of conduction electrons, <i>τ</i>. Therefore, [Formula: see text] is reversible by the magnetic fields, and it takes large value in kagome metals with [Formula: see text] (=lattice constant). Surprisingly, the quantum metric, which defines a fundamental geometric aspect of Bloch wavefunctions, acquires significant momentum dependence in the loop-current phase, resulting in a dramatic enhancement of eMChA by ∼100 times. This research not only clarifies the fundamental symmetry-breaking states in kagome metals but also opens a path for exploring quantum metric-induced phenomena arising from exotic quantum phase transitions in various metals.