Coupling phase enabled level transitions in pseudo-Hermitian magnon-polariton systems
Phys. Rev. B 113, 174413 – Published 14 May, 2026
DOI: https://doi.org/10.1103/dl6v-s896
Abstract
While cavity-magnon hybridization has revealed rich physical phenomena, its practical applications are limited by intrinsic damping in both cavity and magnon modes, a fundamental limitation that leads to short coherence times. Recently, the development of tunable macroscopic gain has shifted the focus of research from purely dissipative systems to gain-loss-balanced non-Hermitian architectures. Here, we present a pseudo-Hermitian model consisting of two magnon modes and two cavity modes arranged in a closed-loop coupling configuration that generates a gauge-invariant coupling phase distinct from conventional phase factors. We establish a direct link between the energy spectra and phase transitions, and observe exceptional points that mark the onset of pseudo-Hermitian symmetry breaking. We further demonstrate both level attraction and level repulsion: the former is associated with four phase transitions and manifests as a double-Z-shaped energy spectrum, while the latter corresponds to two phase transitions characterized by a phase-tunable repulsive gap. In the phase diagram spanned by the non-Hermiticity parameter and the gauge-invariant coupling phase, we uncover a unique correspondence: pseudo-Hermitian symmetry breaking is intrinsically linked to transitions between coherent and dissipative coupling modes, providing new strategies for controlling hybrid magnon-photon quantum states in spintronic systems.
