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Quantum plasmonic non-reciprocity in parity-violating magnets

The optical responses of metals are often dominated by plasmonic resonances - the collective oscillations of interacting electron liquids. Here we unveil a new class of plasmons - quantum metric plasmons (QMPs) - that arise in a wide range of parity violating magnetic metals. In these materials, a dipolar distribution of the quantum metric (a fundamental characteristic of Bloch wavefunctions) produces intrinsic non-reciprocal bulk plasmons. Strikingly, QMP non-reciprocity manifests even when the single-particle dispersion is symmetric: QMPs are sensitive to time-reversal and parity violations hidden in the Bloch wavefunction. In materials with asymmetric single-particle dispersions, quantum metric dipole induced non-reciprocity can continue to dominate at large frequencies. We anticipate that QMPs can be realized in a wide range of parity violating magnets, including twisted bilayer graphene heterostructures, where quantum geometric quantities can achieve large values.