Floquet Chern Insulators of Light

Achieving topologically-protected robust transport in optical systems has recently been of great interest. Most topological photonic structures can be understood by solving the eigenvalue problem of Maxwell's equations for a static linear system. Here, we extend topological phases into dynamically driven nonlinear systems and achieve a Floquet Chern insulator of light in nonlinear photonic crystals (PhCs). Specifically, we start by presenting the Floquet eigenvalue problem in driven two-dimensional PhCs and show it is necessarily non-Hermitian. We then define topological invariants associated with Floquet bands using non-Hermitian topological band theory, and show that topological band gaps with non-zero Chern number can be opened by breaking time-reversal symmetry through the driving field. Furthermore, we show that topological phase transitions between Floquet Chern insulators and normal insulators occur at synthetic Weyl points in a three-dimensional parameter space consisting of two momenta and the driving frequency. Finally, we numerically demonstrate the existence of chiral edge states at the interfaces between a Floquet Chern insulator and normal insulators, where the transport is non-reciprocal and uni-directional. Our work paves the way to further exploring topological phases in driven nonlinear optical systems and their optoelectronic applications, and our method of inducing Floquet topological phases is also applicable to other wave systems, such as phonons, excitons, and polaritons

Method to Select Target Wells and Target Zones for the Technique of Water Plugging

Water shutoff is an effective way to enhance oil recovery and lower water production. It is crucial to select target wells and target zones properly, otherwise, the effect of water shutoff may be disturbed. Traditionally, the job to select target wells and target zones is always done artificially and imprecisely, as a result, water shutoff does not perform as good as it can. This paper proposes a fuzzy method capable of optimizing the selection of target wells and target zones for water shutoff. This study plays a significant role in the technique of water shutoff

Effects of High Magnetic Field and Post-Annealing on the Evaporated Ni/Si (100) Thin Films

The effects of high magnetic field and post-annealing on the structural, electrical and magnetic properties of the evaporated Ni films were investigated and compared. The in-situ application of a 6 T magnetic field during evaporation or post-annealing at 200°C did not change the crystal structures of the films. However, the magnetic field makes the films exhibit the smallest grain size and the lowest surface roughness. Crystallinity was improved for both the 6 T films and the annealed films. This leads to the enhancement of saturation magnetization (Ms). The value of Ms for the 0 T films was 588 emu/cm3, while those for the 6 T films and the post-annealing films without magnetic field were 704 and 647 emu/cm3, respectively. In addition, the 6 T films also exhibited the lowest resistivity. These results indicate that the in-situ application of high magnetic field was a much more efficient method than the post-annealing treatment in the increase of film quality and properties

Structural Evolutions of the Clusters During the Melting and Coalescence Processes

Study on the behaviors of the melting and coalescence of clusters in atomic scale may create new structure at nanoscale, which is a very important research field. The structural evolutions of clusters Cu321, Co321, and Ni321 during their melting and coalescence processes were studied using molecular dynamics simulation with a general embedded atom method in this paper. It was found that the geometries of Cu321 and Co321 transformed to icosahedron from fcc near their melting points, which leads to the increase of their melting points. Concerning the coalescence, it was found that Cu atoms easily formed a coating layer on the surface of Co321 which inhibited the formation of icosahedron in the coalesced complex. The icosahedron was formed during the coalescence of Ni321Co321. These results indicated that the structures were tuned by changing the thermodynamic or coalescence processes

Thyroid metastases from breast cancer: a case report and brief literature review

Thyroid metastasis from breast cancer is a rare occurrence and often indicates a poor prognosis. We report the case of a young female patient with thyroid metastasis from breast cancer after being diagnosed with the Graves’ disease, and review the clinical characteristics and diagnostic approach of thyroid metastases. The mechanism may be associated with altered microenvironment induced by the Graves’ disease and Hashimoto’s thyroiditis. Thyroid function and abnormal imaging examination should be paid attention during breast cancer patients’ follow-up. Early identification and individualized treatment of thyroid metastasis may contribute to prolonged survival and improved quality of life

Geometric similarities and topological phases in surface magnon polaritons

Highly spatially-squeezed polaritons, with propagation momentum significantly larger than free-space modes at the same frequency, enable varied and extreme control over light-matter interaction. Compared to other polaritons, surface magnon polaritons, the magnetic counterpart of surface phonon polaritons, have received relatively little attention. Here, we investigate the dispersion and properties of surface-magnon polaritons, highlighting the impact of geometric similarities and applying them to various surface-magnon polariton devices in both conventional and topological settings. Our theory predicts a method for strongly localizing and significantly enhancing magnetic fields in the microwave range and developing compact and lossless connectors capable of interconnecting waveguides with vastly different input and output impedances. Our work opens new avenues for manipulating magnetic fields in the microwave regime and for exploring topological phases in polariton platforms

High Magnetic Field Annealing Dependent the Morphology and Microstructure of Nanocrystalline Co/Ni Bilayered Films

Co/Ni bilayered films were prepared on ITO glass by electrodeposition assisted with a magnetic field up to 0.5T aligned parallel to the electrode surface. The effect of a high magnetic field annealing up to 12T on morphology and microstructure of the post-deposited films was investigated by field emission scanning electronic microscopy (FE-SEM), X-ray diffraction (XRD) and atomic force microscopy (AFM). Grain shape and grain boundary in the Co/Ni morphology were modified dramatically when the high magnetic field was applied during the annealing process. Magnetic anisotropy appeared in the films due to the preferential orientation of fcc-CoNi alloy in comparison with a weaker orientation of hcp-Co. High magnetic field annealing favored to form a more homogeneous surface with smaller grain size and lower roughness, compared with the annealed samples obtained in the absence of magnetic field. The influencing mechanisms of high magnetic field annealing on the microstructure evolution in the Co/Ni electrodeposits are interpreted in terms of the overlapping effects: diffusion, recrystallization, grain growth and magnetic domains

Observation of Floquet Chern insulators of light

The field of topological photonics studies unique and robust photonic systems that are immune to defects and disorders due to the protection of their underlying topological phases. Mostly implemented in static systems, the studied topological phases are often defined in linear photonic band structures. In this study, we experimentally demonstrate Floquet Chern insulators in periodically driven nonlinear photonic crystals, where the topological phase is controlled by the polarization and the frequency of the driving field. Mediated by strong material nonlinearity, our system enters what we call the 'strong Floquet coupling regime', where the photonic Floquet bands cross and open new energy gaps with non-trivial topology as observed in our transient sum-frequency generation measurements. Our work offers new opportunities to explore the role of classical optical nonlinearity in topological phases and their applications in nonlinear optoelectronics.Comment: 24 pages, 5 figure