Non-Hermitian Topological Magnonics

This platform is ideal for realizing the exceptional point. The Hamiltonian for this phenomenon is the effective Hamiltonian. The term α represents the ferromagnetic resonance damping rate, while the term β represents the bandwidth of the pump induced mode. The coupling strength J depends on the pump power, as shown on the last page. The frequency can be tuned significantly by adjusting the power due to this dependence. The frequency of the pump induced mode is a function of the pump frequency, allowing us to identify two modes as the ferromagnetic resonance. When G equals minus β divided by two times the square root of one, the two modes coalesce into one, revealing the exceptional points. The microwave transmission spectrum shows the realization of the exceptional point, where the two modes are connected and sensitivity is enhanced.