Confining photons in a finite volume is in high demand in modern photonic devices. This motivated decades ago the invention of photonic crystals, featured with a photonic bandgap forbidding light propagation in all directions 1-3 . Recently, inspired by the discoveries of topological insulators (TIs) 4,5 , the confinement of photons with topological protection has been demonstrated in two-dimensional (2D) photonic structures known as photonic TIs 6-8 , with promising applications in topological lasers 9,10 and robust optical delay lines 11 . However, a fully three-dimensional (3D) topological photonic bandgap has never before been achieved. Here, we experimentally demonstrate a 3D photonic TI with an extremely wide (> 25% bandwidth) 3D topological bandgap. The sample consists of split-ring resonators (SRRs) with strong magneto-electric coupling and behaves as a "weak TI", or a stack of 2D quantum spin Hall insulators. Using direct field measurements, we map out both the gapped bulk bandstructure and the Dirac-like dispersion of the photonic surface states, and demonstrate robust photonic propagation along a non-planar surface. Our work extends the family of 3D TIs from fermions to bosons and paves the way for applications in topological photonic cavities, circuits, and lasers in 3D geometries.

Extensive researches have revealed that valley, a binary degree of freedom (DOF), can be an excellent candidate of information carrier. Recently, valley DOF is introduced into photonic systems, and several valley‐Hall photonic topological insulators (PTIs) are experimentally demonstrated. However, in the previous valley‐Hall PTIs, topological kink states only work at a single frequency band, which limits potential applications in multiband waveguides, filters, communications, and so on. To overcome this challenge, here a valley‐Hall PTI, where the topological kink states exist at two separated frequency bands, is experimentally demonstrated in a microwave substrate‐integrated circuitry. Both the simulated and experimental results demonstrate the dual‐band valley‐Hall topological kink states are robust against the sharp bends of the internal domain wall with negligible intervalley scattering. This work may pave the way for multichannel substrate‐integrated photonic devices with high efficiency and high capacity for information communications and processing.

Valley degrees of freedom, providing a novel way to increase capacity and efficiency of information processing, have become an important instrument for photonics. Experimental studies on photonic topological valley kink states at interfaces between regions with opposite valley‐Chern numbers have attracted much attention; however, they are restricted to zigzag‐type interfaces, largely limiting their applications such as geometry‐dependent topological channel intersections. Here, valley kink states at generic interfaces in subwavelength substrate‐integrated photonic circuitry are experimentally demonstrated and manipulated. The robustness of the kink states is verified by measuring transmissions of the kink states through twisted interfaces and interfaces with disorders. Based on the valley kink states at generic interfaces, several topological channel intersections where photonic transport paths are related to geometries of the intersections are realized. In comparison to those in previous work, these valley photonic crystals have subwavelength thicknesses and excellent self‐consistent electrical shielding, which are perfectly compatible with conventional substrate‐integrated photonic circuitry. This work opens a door to manipulate photonic valley pseudo‐spins in lightweight substrate‐integrated circuitry with robustness and easy access.

11Aiming at an atomistic mechanism of heavy metal cation complexing on clay surfaces, we 12 carried out systematic first principles molecular dynamics (FPMD) simulations to investigate the 13 structures, free energies and acidity constants of Ni(II) complexes formed on edge surfaces of 14 2:1 phyllosilicates. Three representative complexes were studied, including monodentate 15 complex on the ≡SiO site, bidentate complex on the ≡Al(OH) 2 site, and tetradentate complex on 16 the octahedral vacancy where Ni(II) fits well into the lattice. The complexes structures were 17 characterized in detail. Computed free energy values indicate that the tetradentate complex is 18 significantly more stable than the other two. The calculated acidity constants indicate that the 19 tetradentate complex can get deprotonated (pKa=8.4) at the ambient conditions whereas the other 20 two hardly deprotonate due to extremely high pKa values. By comparing with the 2 Site 21 Protolysis Non Electrostatic Surface Complexation and Cation Exchange (2SPNE SC/CE) model, 22 Peacock and Sherman, 2005; Tan et al. Tournassat et al., 2013). In the past two decades, 48 the 2SPNE SC/EC (i.e., 2 site protolysis non electrostatic surface complexation and cation 49 exchange) model has been extensively and successfully applied to characterize the sorption of 50 many metal cations (e.g., Ni(II), Zn(II), Cd(II), Fe(II), Eu(III), Cm(III)) on 2:1-type clay 51 minerals Bradbury and Baeyens, 1997 Bradbury 52 et al., 2005;Soltermann et al., 2014;Soltermann et al., 2013). For the complexation on edge 53 surface, in the modelling of sorption isotherm, two types of edge sites have been used to fit the 54 adsorption data, commonly referred to be the strong site (S S OH) and the weak site (S W1 OH) 55 . The strong site has a high binding affinity and a low site capacity 56(2 mmol/kg), while the weak site has a lower affinity and a higher site capacity (40 mmol/kg) 57 . 58 Advanced spectroscopic methods have been broadly used to derive possible complexing sites 59 for heavy metal cations. For example, Schlegel et al. (1999) investigated the sorption of Co(II) 60 on edge surfaces of hectorite by polarized EXAFS (extended X-ray absorption fine structure) 61 technique and found the formation of mononuclear complexes (Schlegel et al., 1999). EXAFS 62 study indicated that Ni(II) formed inner-sphere mononuclear complexes at montmorillonite 63 edges via corner-sharing pattern between Si tetrahedra and Ni(II) octahedra and edge-sharing 64 pattern between Al octahedra and Ni(II) octahedra (Dähn et al., 2003). By modelling Zn(II) 65 sorption isotherm with the 2SPNE SC/EC model and measuring EXAFS spectra, Dähn et al. 66have demonstrated the existence of two types of edge complexing sites, which agrees with the 67 concept of the strong/weak site (Dähn et al., 2011). Atomistic simulations and measured EXAFS 68 spectra suggested that Zn(II) was incorporated into the octahedra on clay edges at low loading 69 and formed inner-sphere complexes on octahedral sites at medium loading (...

In this study, the structures and acidity constants (p K's) of uranyl arsenate complexes in solutions have been revealed by using the first principle molecular dynamics technique. The results show that uranyl and arsenate form stable complexes with the U/As ratios of 1:1 and 1:2, and the bidentate complexation between U and As is highly favored. Speciation-pH distributions are derived based on free energy and p K calculations, which indicate that for the 1:1 species, UO(HAsO)(HO) is the major species at pH < 7, while UO(HAsO)(HO) and UO(AsO)(HO) dominate in acid-to-alkaline and extreme alkaline pH ranges. For the 1:2 species, UO(HAsO)(HO) is dominant under acid-to-neutral pH conditions, while UO(HAsO)(HAsO)(HO), UO(HAsO)(HAsO)(HO), and UO(AsO)(HAsO)(HO) become the major forms in the pH range of 7.2-10.7, 10.7-12.1, and >12.1, respectively.