Quantum Plasmonic Nonreciprocity in Parity-Violating Magnets

Abstract

The optical responses of metals are often dominated by plasmonic resonances, that is, 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 wave functions) produces intrinsic nonreciprocal bulk plasmons. Strikingly, QMP nonreciprocity manifests even when the single-particle dispersion is symmetric: QMPs are sensitive to time-reversal and parity violations hidden in the Bloch wave function. In materials with asymmetric single-particle dispersions, quantum metric dipole induced nonreciprocity 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.

Quantum metric nonlinear Hall effect in a topological antiferromagnetic heterostructure

“…The intrinsic second-order Hall effect observed here realizes an electrical nonlinearity induced by the AFM spins and provides a rare example of a quantum metric response. As highlighted by recent theoretical studies, the influence of the quantum metric is expected to span many different areas, ranging from nonlinear responses in PT-symmetric AFMs to flat-band conductivity, superconductivity and charge orders in moiré systems, the fractional Chern insulator, and k-space dual of gravity (20,(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34). Another interesting future direction is to explore the nonlinear responses in canted AFM materials [section V.3 of ( 19)], where nonzero Berry curvature of higher order in magnetization has recently been observed (38,46,51).…”

“…However, the way quantum metric regulates electronic motion remains largely unknown. Recently, theories have predicted a wide range of exotic quantum metric responses (20,(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34).…”