Magnetic equivalent of electric superradiance in yttrium-iron-garnet films

A dense system of independent oscillators, connected only by their interaction with the same cavity excitation mode, will radiate coherently, which effect is termed superradiance. In several cases, especially if the density of oscillators is high, the superradiant decay of the oscillators' excited state may dominate the intrinsic relaxation processes. At low frequencies, this limit can be achieved with cyclotron resonance in two-dimensional electron gases. In those experiments, the cyclotron resonance is coupled to the electric field of light, while the oscillator density can be easily controlled by varying the gate voltage. However, in the case of magnetic oscillators, to achieve the dominance of superradiance is more tricky, as material parameters limit the oscillator density, and the magnetic coupling to the light wave is rather weak. Here we present quasi-optical magnetic resonance experiments on thin films of yttrium iron garnet. Due to the simplicity of experimental geometry, the intrinsic damping and the contribution of superradiance can be easily separated in the transmission spectra. We show that with increasing film thickness, the losses due to coherent radiation prevail the system's internal broadening. Magnons are oscillating magnetic waves that can be engineered using nanoscale structures and are expected to have useful applications in future information processing and storage devices. Here, the authors investigate magnetic superradiance as a possible mechanism limiting the lifetime of the magnonic excitations in thin films.

Automated summary

A dense system of independent oscillators connected only by interacting with the same cavity excitation mode will radiate coherently in a phenomenon called superradiance. Experimental investigations on yttrium iron garnet thin films show that with increasing film thickness, losses due to coherent radiation dominate the system's internal broadening.