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We experimentally study the fast–slow light induced by multiple-path microwave interference in the yttrium iron garnet (YIG)-microstrip cavity system. The destructive interference between two types of paths, the direct path through the traveling wave and the indirect paths through the magnon and the resonator, leads to a nearly blocking of microwave transmission when the magnon mode resonates at a particular frequency. This phenomenon is accompanied by a dramatic evolution to the phase of microwave transmission, which strongly adjusts the group velocity of light. Tuning the magnon mode crossing the particular frequency by controlling the external magnetic field, the polarity of phase evolution will be reversed, which presents as a switch between phase delay (slow-light) and phase advance (fast-light). And we experimentally achieve the broadband fast–slow light by tuning the external damping of the magnon. Furthermore, we predict the broadband fast–slow light in different physical parameters. Our results demonstrate that the destructive interference in the YIG-microstrip cavity system is a way to manipulate fast–slow light, which has a great significance in quantum information processing and storage. • We demonstrated the switchable fast–slow light by tuning the external magnetic field. • We realized the broadband fast–slow light by manipulating the external damping of magnon. • We predicated the broadband fast–slow light associated with different physical parameters. [ABSTRACT FROM AUTHOR]

We reveal the multiple-path microwave interference induced microwave transmission in a cavity-magnonic system composed of a yttrium-iron-garnet (YIG) film and a microstrip cavity circuit. By changing the position of the YIG in the circuit, we identify that the magnon in YIG is driven by the standing microwave from the cavity or by the traveling wave through the microstrip. We observe that the microwave transmission spectra show an anti-crossing dispersion named mode repulsion and an anomalous dispersion named mode attraction , respectively. The characteristic of anti-cross dispersion spectra is theoretically predicted using the coupling between the magnon and the cavity. Without coupling, the anomalous dispersion in our experiment is well interpreted by the multiple-path microwave interference between the indirect paths through the cavity and the magnon and the direct path through the traveling wave. And the anomalous dispersion is caused by the redistribution of the microwave transmission intensity. We also find the phases of the magnon in two cases changes π , which can be the key physical factor to understand the change of microwave transmission characteristics. Our work highlights the role played by the multiple-path microwave interference in magnonic microwave devices, which will be an important issue in designing microwave circuits based on the magnon. • The multiple-path microwave interference can lead to an anomalous dispersion. • Demonstrate that the anomalous dispersion is caused by the redistribution of microwave transmission intensity. • Verify the phase of magnon changes π between the anti-cross dispersion and the anomalous dispersion. [ABSTRACT FROM AUTHOR]