Dissipative coupling of resonators arising from their cooperative dampings to a common reservoir induces intriguingly new physics such as energy level attraction. In this study, we report the nonlinear properties in a dissipatively coupled cavity magnonic system. A magnetic material yttrium iron garnet is placed at the magnetic field node of a Fabry-Perot-like microwave cavity such that the magnons and cavity photons are dissipatively coupled. Under high power excitation, a nonlinear effect is observed in the transmission spectra, showing bistable behaviors. The observed bistabilities are manifested as clockwise, counterclockwise, and butterfly-like hysteresis loops with different frequency detuning. The experimental results are well explained as a Duffing oscillator dissipatively coupled with a harmonic one and the required trigger condition for bistability could be determined quantitatively by the coupled oscillator model. Our results demonstrate that the magnon damping has been suppressed by the dissipative interaction, which thereby reduces the threshold for conventional magnon Kerr bistability. This work sheds light on potential applications in developing low power nonlinearity devices, enhanced anharmonicity sensors and for exploring the non-Hermitian physics of cavity magnonics in the nonlinear regime.

Bound states in the continuum (BICs) present a unique solution for eliminating radiation loss. So far, most reported BICs are observed in transmission spectra, with only a few exceptions being in reflection spectra. The correlation between reflection BICs (r-BICs) and transmission BICs (t-BICs) remains unclear. Here, we report the presence of both r-BICs and t-BICs in a three-mode cavity magnonics. We develop a generalized framework of non-Hermitian scattering Hamiltonians to explain the observed bidirectional r-BICs and unidirectional t-BICs. In addition, we find the emergence of an ideal isolation point in the complex frequency plane, where the isolation direction can be switched by fine frequency detuning, thanks to chiral symmetry protection. Our results demonstrate the potential of cavity magnonics and also extend the conventional BICs theory through the application of a more generalized effective Hamiltonians theory. This work offers an alternative idea for designing functional devices in general wave optics.

The topology of the photonic bath shows excellent potential to engineer the intriguing interaction properties between light and matter. Here, we study the dielectric resonator array with a zigzag geometry, an analogy of the Su-Schrieffer-Heeger model equipped with peculiar freedom to manipulate the nearest-neighbor coupling strength by the internal interaction. A staggered coupling strength of $s$-type pillar modes is experimentally achieved via the photonic spin-orbit coupling by employing the zigzag dielectric resonator chain. As a result, we observe that the robust edge states of the zigzag chains manifest themselves with linear polarization for an even number of dielectric resonators but elliptical polarization for an odd number. In addition, by coupling magnons to the topological waveguide, we observe resonant magnon–magnon–edge-state coupling, whose coupling strength is topologically protected. More broadly, our work shows that topological waveguide-QED systems may provide the potential for synthesis and study of many-body states with attractive long-range interaction.

Backward erosion piping, which is one of the leading causes of levee and dam failures, is more likely to occur when a flow is concentrated on a defect with an overlying low-permeability layer and a shallow erosion channel forming and progressing towards a seepage source. Two analytical models are presented to allow assessment of the seepage regime on the initiation stage of BEP. The variations between the two models are analysed, indicating that the effects of soil loosening have a major role in the assessment of BEP mechanisms. This paper also describes the reliability of using Xiao’s model in 3D analysis, which includes results and parametric analysis. Although the head in front of the tip of the erosion channel can be predicted by this accepted calculation model, which is essential for laboratory work on this topic, the model also has range and boundary limitations that need to be addressed for general prediction when BEP progresses with channel development.

A fully penetrating cut-off wall is a vertical seepage barrier that fully penetrates an aquifer and is embedded in an underlying aquitard to a certain depth. Groundwater seepage with this type of wall occurs through three paths: leakage through the body of the wall in the aquifer, leakage through the body of the wall embedded in the aquitard, and seepage under the wall. Seepage through the first path can be simply treated as one-dimensional flow. However, due to the mutual influence of seepage through the latter two paths, the seepage problem is complicated and still needs to be studied. An analytical method is proposed to solve this problem in this study. Mathematic expressions for flow rate and head value are obtained by superposition of drawdowns of two exact models, namely, the model with only leakage through the wall body and the model with only seepage under the wall, respectively. Exact solutions are quoted or derived for the exact models, but they involve Legendre’s elliptic integrals of the first and third kinds. To facilitate an engineering application, approximate models of the exact models are introduced and their solutions are applied to the analytical formulas. The accuracy and applicability of the proposed method are verified compared with the numerical method. The proposed method provides a simple but effective method for quickly estimating the quantity of seepage in the aquitard (including leakage through the wall body and seepage under the wall) when simultaneously considering the effects of wall permeability and thickness.

Cavity magnonics provides a versatile platform to tune the photon-magnon interaction bringing about promising applications for quantum information processing. Here, we implement a metamaterial planar cavity to suppress the radiative damping by engineering the symmetry of the cavity configuration. Then, the mode with suppressed radiative damping, i.e., dark mode, is coupled to the magnon mode in a thin yttrium iron garnet film ($5\mu \mathrm{m}$), which is detected by performing the reflection measurements and spin-pumping experiment. Pronounced anticrossing of the ferromagnetic resonance and the cavity dark mode is observed, where the largest coupling strength reaches 2.5% of the resonant cavity frequency. In addition, the spin wave resonances along the thickness direction are identified, which enhances the spin-pumping signal when they coalesce with the hybridized cavity-magnon-polariton mode. The dark mode excited by the planar metamaterial cavity leads to an improvement in the coherent manipulation of the spin current.