Bistability of Cavity Magnon-Polaritons

We experimentally demonstrate the magnon-polariton bistability in a cavity magnonics system consisting of cavity photons strongly interacting with the Kittel-mode magnons in a small yttrium iron garnet (YIG) sphere. The bistable behaviors are emerged as sharp frequency switchings of the cavity magnon-polaritons and related to the transition between states with large and small number of polaritons. In our experiment, we align, respectively, the [100] and [110] crystallographic axes of the YIG sphere parallel to the static magnetic field and find very different bistable behaviors (blue- and red-shift of the polariton frequency) in these two cases. The experimental results are well fitted and explained as being due to the Kerr nonlinearity with either positive or negative coefficient. Moreover, in the large dispersive regime, we observe simultaneous bistability of both lower branch (more magnons) and upper branch (more photons) polaritons by applying a drive field on the lower branch.