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

Justin T. Hou | Pengxiang Zhang | Luqiao Liu

Spin-torque oscillators (STOs) have found applications in microwave generation, detection, and neuromorphic computing. Despite extensive studies in the past 20 years, the active region of a single STO is still limited to the nanometer scale due to inevitable magnon-magnon scatterings. Because of the small size, a single STO suffers from low output power and a broadened linewidth due to thermal fluctuations.
In this work, we propose a novel microwave generation device enabled by spin-photon coupling—a spin-torque-oscillator maser, by placing a STO inside a microwave photon cavity. With numerical simulation and analytical proof, we show that highly coherent magnetic self-oscillation with high power and a narrow linewidth can be realized in a large area ferromagnetic thin film, breaking the limitations on conventional STOs. Our theoretical proposal represents a step towards the experimental realization of an on-chip, scalable, electrically-driven, continuous-wave maser for applications in both the classical and the quantum electronics domains.

Funding Sources: Air Force Office of Scientific Research (AFOSR) Grant No. FA9550-19-1-0048 | National Science Foundation (NSF) Grant No. ECCS-1653553 | Mathworks Fellowship