Prediction of antimagnon-polarons with intrinsic momentum-space level attraction

Abstract

Propagating hybrid quasiparticles formed by magnons and phonons (magnon-polarons) or photons (magnon-polaritons) typically exhibit level repulsion in momentum space. Level attraction, by contrast, requires an anti-phase channel and has so far been restricted to zero-dimensional systems mediated by dissipative baths. Here we predict the antimagnon-polaron in a continuous magnetoelastic medium, which inherently exhibits momentum-space level attraction. The spin-orbit-torque (SOT)-stabilized antimagnon precesses with opposite handedness, directly reversing the magnetoelastic coupling without requiring an external environment. This intrinsic attraction yields a distinctive 0/π phase-locked simultaneous growth. Micromagnetic simulations confirm this picture, revealing that the SOT-controlled balance between gain and damping drives a collective instability. This ultimately enables a continuously tunable, dc-pumped, single-frequency phonon laser, establishing a novel route for coherent acoustic emission.