Quantum metric plasmons: quantum geometry enriched intrinsic bulk non-reciprocal plasmonics

Bloch quantum geometry holds immense potential to reveal new possibilities in light-matter interaction. Here, we unveil one such possibility by illustrating a new class of plasmons – quantum metric plasmons (QMPs), in strongly interacting Fermi liquids. QMPs are determined by Bloch wavefunction texture, and thus possess intrinsic non-reciprocity, i.e., ω(q) ≠ ω(-q), in the bulk. This is in contrast to currently available schemes utilizing out of equilibrium driving or magnetohydrodynamics for non-reciprocal plasmonic responses. We show that QMPs are passively generated by bulk directional currents in presence of broken parity and time reversal symmetries. Interestingly, we find that QMPs can even thrive in symmetric bands by responding to the parity and time reversal symmetry violations hidden in the Bloch wavefunction. We anticipate that QMPs can be realized in readily available parity-violating magnets, especially in moiré heterostructures where the quantum geometric responses are pronounced (e.g., twisted bilayer graphene heterostructures).