Proposal for a Spin-Torque-Oscillator Maser Enabled by Microwave Photon-Spin Coupling

We study a direct-current-driven maser device enabled by spin-photon coupling, where coherent magnetic self-oscillation can be realized in large-area ferromagnetic thin film under the excitation of spin-orbit torques. show via both micromagnetic simulation and analytical derivation that above critical value coupling strength between spin-torque oscillator microwave resonator, oscillation develops macroscopic phase coherence, narrow linewidth, becomes phase-locked with photon mode. The threshold for synchronizing individual spins reduces as sample dimension increases, suggesting spin-torque-oscillator readily using thin-film ferromagnets without relying on confinement. Moreover, mode directly provide emission, which exhibits enhanced power reduced linewidth an increasing number spins, leading to useful approach developing highly on-chip sources.