Pseudo-Hermitian magnon-polariton system with a three-dimensional exceptional surface
Vahram L. Grigoryan, Ke Xia
Abstract
We introduce a non-Hermitian platform allowing us to obtain a three-dimensional exceptional surface in a magnon-polariton coupled system. A two-tone driving system gives rise to a complex effective coupling, leading to a pseudo-Hermitian Hamiltonian. Independent tuning of the real and imaginary components of the coupling provides additional degrees of freedom, allowing us to form a four-dimensional parameter space in which a three-dimensional exceptional surface is proposed. We show that this pseudo-Hermitian Hamiltonian has the most general form in cavity spintronics with $CPT$ symmetry. Our exceptional surface allows us to form a $\mathcal{PT}$-like circle where the $\mathcal{PT}$ and anti-$\mathcal{PT}$-symmetric exceptional points are unified. Moreover, we show that the $CPT$ symmetry in our system can be reduced to $\mathcal{PT}$ symmetry. Our proposal makes the cavity magnon polariton a rich platform for realizing intriguing phenomena of exceptional points regardless of fabrication imperfections or exact detuning of the system frequencies.