Spin Cavitronics

Promising fields like quantum simulation, information, nano-scale (quantum) thermodynamics etc. have been dominated in the past by photonics, optomechanics, cold atoms, NV centers, Josephson junctions, and semiconductor quantum dots. However, the strong coupling of spin waves (or their quanta, the magnons) to microwave modes in high finesse cavities and other experimental breakthroughs, hold the promise of a magnon-based platform for macroscopic quantum effects. We therefore theoretically explore the coherent coupling of magnons with other (quasi-)particles such as photons, phonons, Cooperons, etc., in order to extend the fields of spintronics, spin caloritronics, and spin mechanics into uncharted regimes. The figure below illustrates some of the issues in spin cavitronics.

Fig. 1. (a) is a picture of a cylindrical microwave cavity that is loaded by one or mode samples as described in (b). The properties of the microwave and their coupling to the samples can be accessed by the transmission or reflection of the microwaves via "ports". (b) Top panel: The load might consist of one magnet or more magnets (often in the form of spheres) positioned strategically. e.g., at antinodes of the magnetic field of the standing microwaves. Bottom panel: Two example systems that can couple strongly with the magnets via cavity photons, such as superconducting (SC) circuits including Josephson Junctions (JJ) or nanoelectromechanical systems (NEMS). (c) The low-energy spin wave dispersion relation is anisotropic and non-monotonous, as is shown here for a thin film with in-plane magnetization. (d) Mode dispersion for a magnetic sphere is similar to (c) but discrete. Texture of two representative spin wave modes in a sphere is shown. For a sphere of 10 micrometer radius, these modes correspond to the points in (c) indicated by arrows.