Crystal State Research Articles

Flat Landau levels and interface states in two-dimensional photonic crystals with a nodal ring

Flat Landau levels and interface states in two-dimensional photonic crystals with a nodal ring

Observation of double-kink states in multivalley acoustic crystals

Observation of double-kink states in multivalley acoustic crystals

Dual-polarization helical interface states in inverse-designed photonic crystals with glide symmetry

Dual-polarization helical interface states in inverse-designed photonic crystals with glide symmetry

Growth, Structure and Thermal Properties of LuGdVO4 Mixed Crystal

The high quality mixed crystal with near stoichiometric Lu0.5Gd0.5VO4 has been grown successfully by the Czochralski method. The composition, structure and thermal properties were studied. First, the growth conditions and crystal quality were analyzed. The thermal properties of the crystal were studied by analyzing specific heat, thermal expansion coefficients and thermal diffusivity. And the X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS) were used to analyze the crystal structure, atomic vibrations and chemical states. The results show that Lu0.5Gd0.5VO4 crystal can be an excellent candidate laser matrix material.

Localized modes in platinum aluminides

Platinum aluminides have the prospect of being used as both functional and structural materials for a range of scientific and technical tasks. They possess unique properties that make them effective catalysts. The dynamics of the crystal lattice play an important role in the manifestation of these properties. In this study, an analysis of the density of phonon states of crystals and the possibility of the existence of localized lattice vibrations in Al and Pt alloys is conducted using atomistic modeling. The following compounds are considered: AlPt, Al2Pt, Al3Pt, AlPt2, Al3Pt5, AlPt3 (four types of lattices). The calculated phonon spectra allow for the assessment of the possibility of the existence of nonlinear localized modes in the forbidden zone of the spectrum, if it is present. It is shown that a number of crystals within the framework of the considered formalism and interatomic potential can have a forbidden zone. This condition, together with the nonlinearity of the bonds, ensures the existence of highly-amplitude localized modes in the following compounds: AlPt3, AlPt3(1), AlPt3(2), AlPt3(3). It is also established that in the Al3Pt5 alloy, the existence of prolonged high-amplitude excitations on the Al atom is possible.

Spotlight: Visualization of Moiré Quantum Phenomena in Transition Metal Dichalcogenide with Scanning Tunneling Microscopy.

Transition metal dichalcogenide (TMD) moiré superlattices have emerged as a significant area of study in condensed matter physics. Thanks to their superior optical properties, tunable electronic band structure, strong Coulomb interactions, and quenched electron kinetic energy, they offer exciting avenues to explore correlated quantum phenomena, topological properties, and light-matter interactions. In recent years, scanning tunneling microscopy (STM) has made significant impacts on the study of these fields by enabling intrinsic surface visualization and spectroscopic measurements with unprecedented atomic scale detail. Here, we spotlight the key findings and innovative developments in imaging and characterization of TMD heterostructures via STM, from its initial implementation on the in situ grown sample to the latest photocurrent tunneling microscopy. The evolution in sample design, progressing from a conductive to an insulating substrate, has not only expanded our control over TMD moiré superlattices but also promoted an understanding of their structures and strongly correlated properties, such as the structural reconstruction and formation of generalized two-dimensional Wigner crystal states. In addition to highlighting recent advancements, we outline upcoming challenges, suggest the direction of future research, and advocate for the versatile use of STM to further comprehend and manipulate the quantum dynamics in TMD moiré superlattices.

Multiple topological states in photonic crystals with generalized Kekulé modulation

We theoretically proposed a feasible way to design multi-topological states in one two-dimensional photonic crystal (PC). By sliding and rotating the meta-atoms of its unit cell, the topological phase of the PC can be continuously tuned, but without a closing of bandgap; it is similar to the Kekulé modulation in honeycomb lattices. We first show the existence of helical topological edge states in conventional topological insulator, which intersect together and form a Dirac cone in the two-dimensional synthetic space of the PC. Then, in full synthetic space, the PC behaves high-order topological insulator, and the corner state is then constructed in a heterostructure that consists of three different PCs. Furthermore, we demonstrate the photonic crystal with non-uniform modulation can behaves as a splitter and a rainbow trapper. Our proposal may provide interesting insight for designing of multiple topological states, which have potential in photonic on-chip devices.

Mapping charge excitations in generalized Wigner crystals.

Transition metal dichalcogenide-based moiré superlattices exhibit strong electron-electron correlations, thus giving rise to strongly correlated quantum phenomena such as generalized Wigner crystal states. Evidence of Wigner crystals in transition metal dichalcogenide moire superlattices has been widely reported from various optical spectroscopy and electrical conductivity measurements, while their microscopic nature has been limited to the basic lattice structure. Theoretical studies predict that unusual quasiparticle excitations across the correlated gap between upper and lower Hubbard bands can arise due to long-range Coulomb interactions in generalized Wigner crystal states. However, the microscopic proof of such quasiparticle excitations is challenging because of the low excitation energy of the Wigner crystal. Here we describe a scanning single-electron charging spectroscopy technique with nanometre spatial resolution and single-electron charge resolution that enables us to directly image electron and hole wavefunctions and to determine the thermodynamic gap of generalized Wigner crystal states in twisted WS2 moiré heterostructures. High-resolution scanning single-electron charging spectroscopy combines scanning tunnelling microscopy with a monolayer graphene sensing layer, thus enabling the generation of individual electron and hole quasiparticles in generalized Wigner crystals. We show that electron and hole quasiparticles have complementary wavefunction distributions and that thermodynamic gaps of ∼50 meV exist for the 1/3 and 2/3 generalized Wigner crystal states in twisted WS2.

Amine‐Free Multi‐Faceted CsPbBr3 Nanocrystals for Complete Suppression of Long‐Lived Dark States

AbstractConventional amine‐capped perovskite nanocrystals (A‐PNCs) often show microscopic fluctuation (blinking) of photoluminescence (PL) between bright and near‐background (dark) states. The transient dark phases spanning milliseconds (ms) to several seconds timescale typically owe to the non‐radiative (NR) fate of charge carriers in crystal defect states, limiting the PNC's efficiency in optoelectronics. A PL study of a novel trioctylphosphine (TOP) capped rhombic cuboctahedron‐shaped amine‐free (AF) PNC is presented, demonstrating their fascinating nonblinking nature. While oleylamine‐capped hexahedron A‐PNCs as a reference system show long dark states, their population is completely suppressed in ≈90% of AF‐PNCs with random large‐amplitude PL fluctuations several times above the background. The PL trajectories of AF‐PNCs primarily comprise constant power spectral densities (PSDs) which are unprecedented and deviate from power‐law distribution as observed for A‐PNCs and most of the other blinking nanocrystals. Such signature of PSDs and frame‐by‐frame intensity jump analysis indicate a fast (<<ms) timescale charge‐carrier dynamics governing the PL emission of AF‐PNCs, likely involving short‐lived metastable states. Besides, long‐term stability and suppressed dark phases in ≈70% AF‐PNCs even 90 days after the synthesis is noteworthy. Altogether the study provides exceptional optical characteristics of photostable amine‐free PNCs which would be attractive to exploit in commercial display applications.

Valley kink states and valley-polarized chiral edge states in substrate-integrated topological photonic crystals

Valley kink states and valley-polarized chiral edge states in substrate-integrated topological photonic crystals

Tetraphenylethylene fused pyrrolo[3,2-b]pyrrole derivatives with reversible mechanofluorochromic and aggregation-induced emission enhancement characteristics

Modification on typical of molecular unit with aggregation-induced emission (AIE)/aggregation-induced emission enhancement (AIEE) can play a important role in obtaining solid-state fluorescence materials and mechanofluorochromic (MFC) materials. We utilize the multicomponent reaction of TPE-containing aldehyde, arylamine and butane-2,3-dione in the presence of iron(III) perchlorate to design and synthesize two novel MFC materials by combination of the tetraphenylethylene (TPE) and pyrrolo [3,2-b]pyrrole core units. Investigation of CHW-1 and CHW-2 aggregation-induced emission behaviors indicated that these materials all exhibited AIEE properties. Subsequent mechanochromic luminescence tests exhibited reversible mechanochromism natures that involve fluorescent color change from green to yellow (Grinding-induced spectral shift (△λ): 35 nm and 38 nm, respectively). Then the datas (including SEM, PXRD and DSC) revealed that this mechanofluorochromism was ascribed to the transformation of crystal state to the amorphous form. Moreover, CHW-1 and CHW-2 could be applied for optical recording devices and security printing.

Fluorinated liquid crystals and their mixtures giving polar phases with enhanced low-temperature stability

ABSTRACT The fluid ferroelectrics, called ferroelectric nematics (NF), have recently become available by incorporating strong polarity into rod-shaped liquid crystal molecules. Its unprecedented electro-optic properties have created significant excitement in soft matter research. The further progression from the NF phase to the antiferroelectric smectic Z (SmZA) phase, and ultimately to the ferroelectric Smectic A (SmAF) phase, represents a remarkable journey in emerging polar liquid crystal states. Nevertheless, the limitation of NF liquid crystal materials remains one of the prominent obstacles to physical property optimization and optoelectronic device development. In this work, we synthesized a series of fluorinated liquid crystal molecules with large dipole moments and systematically investigated their phase behavior. We designed them with a similar fluorinated aromatic skeleton and varied the structures of the terminal group and bridging bond. We found that the dipole moment density and shape anisotropy significantly affect the phase behavior. Notably, diverse polar liquid crystal phases, including NF, SmZA, and SmAF were observed. Through a multi-component mixing strategy, we successfully achieved a much-expanded temperature window and improved low-temperature stability not only in the NF phase but also in the SmZA and SmAF phases.

Physico-chemical properties of illite in the organic matter (OM)-rich claystone of Nankai Trough contrast with coeval OM-poor claystone: IODP Expedition 348

Naturally occurring microbially induced smectite-to-illite (Sm-I) reaction is of great interest to understand the control for the conventional Sm-I transformation, the source of bioavailable iron (Fe) in sediments, and the evolution of the microbial community in the deep biosphere. Direct comparisons of physico-chemical properties of illite-like phases including collapsed high-charge smectite and transient phase, and mature illite were performed for the organic matter (OM)-rich claystone in contrast with those of coeval OM-poor claystone (2163 m–2217 m below sea floor) buried at Nankai Trough (Integrated Ocean Discovery Program Site C0002). These clay layers are interbedded with 70°–90° dipping angle, such that they have nearly identical burial conditions of temperature, time, and fluid geochemistry except for OM content, one of the significant controls that can fuel heterotrophic microbial Fe (III) reduction. Unlike the abiotic Sm-I reaction, the local variations in the crystal structure, elemental composition, and oxidation states of Fe for the illite and illite-like phases in the OM-rich claystone suggest that illitization is promoted through the reduction of structural Fe (III) in smectite by microbial activity, however the effects of OM cannot be ruled out.

Ultraviolet Organic Laser from Rhombus Microcrystal: Benefits of Single-Molecule Emission from Twisted Structure.

Light-emitting molecular crystals with efficient emission behavior are crucial for fabricating low-threshold ultraviolet organic lasers. Herein, we demonstrated a rhombus microcrystal from a fluorene-based conjugated molecule (CL-1) with robust emission behavior for an ultraviolet organic laser. Due to the synergistic effect of twisted intramolecular conformation and weak π-interaction, the CL-1 single crystal showed an extremely high photoluminescence quantum yield (PLQY) of ∼82%, due to their single-molecule excitonic behavior. Considering the diverse noncovalent interactions, CL-1 molecules easily self-assembled into the rhombus microcrystals. Finally, a low-threshold ultraviolet organic laser was fabricated with a sharp emission at 379 nm, attributed to the 0-1 vibration band of a single CL-1 molecule, also further confirming the single twisted-molecule emission in crystal states. Precisely controlling the intramolecular twisted structure and intermolecular interaction of organic conjugated molecules is a precondition to obtain robust ultraviolet emission for optoelectronic applications.

In-Gap Edge and Domain-Wall States in Largely Perturbed Phononic Su–Schrieffer–Heeger Lattices

Topological states of matter have attracted significant attention due to their intrinsic wave-guiding and localization capabilities robust against disorders and defects in electronic, photonic, and phononic systems. Despite the above topological features that phononic crystals share with their electronic and photonic counterparts, finite-frequency topological states in phononic crystals may not always survive. In this work, we discuss the survivability of topological states in Su–Schrieffer–Heeger models with both local and non-local interactions and larger symmetry perturbation. Although such a discussion is still about ideal mass-spring models, the insights from this study set the expectations for continuum phononic crystals, which can further instruct the application of phononic crystals for practical purposes.

Formation of perovskite by solid-gas reaction through low-temperature carbon counter electrode in hole-conductor-free perovskite solar cells

Recently, hole-conductor-free perovskite solar cells (PSCs) with carbon counter electrode (CCE) have attracted great attention for its high stability and low fabrication cost. Furthermore, it would lower the cost and simplify the manufacturing process of PSCs by low temperature processing instead of high temperature sintering for fabrication. In this case, however, it is very important to improve the interfacial contact between perovskite layer and CCE. In this work, we for the first time introduce solid-gas reaction between dimethylammonium lead iodide (DMAPbI3) in solid state under carbon layer and methylamine (MA) gas passed through CCE which is formed at low temperature of 120 ℃. Based on Brunauer-Emmett-Teller (BET) measurement and XRD analysis, it is found that MA gas can pass through our low-temperature CCE and perovskite crystals could be successfully formed by the reaction with DMAPbI3. In this case, due to the existence of liquid crystal intermediate state and volume expansion, interfacial contact would become better and the charge transfer and recombination characteristics have improved considerably. The best performance devices based on optimized MA gas treatment time exhibit higher efficiency of 12.4% than that of PSCs fabricated by conventional ways with low-temperature processed CCE (9.6%).

Hydrothermally synthesized MnCo2O4 nanoparticles for advanced energy storage applications

We observed the impact of reaction time on the electrochemical performance of MnCo2O4 nanoparticles, specifically focusing on the overgrowth of nanoparticles over the nanostructure. We characterized the synthesized nanomaterial using XRD, SEM, and XPS techniques to analyze its crystal structure, surface microstructure, and chemical states, respectively. The electrode prepared via a 5-hour hydrothermal reaction exhibited an outstanding areal capacitance of 144 mF/cm2 at a current density of 1A/g. Furthermore, it demonstrated an areal energy density of 4.1 μWh/cm2 at a power density of 0.225 mW/cm2. We assembled an asymmetric supercapacitor (ASC) configuration, MCO-5 h//AC, using MCO-5 h and activated carbon (AC), which showcased exceptional areal capacitance, areal energy density, and power density. These characteristics make it highly suitable for practical applications in energy storage. Overall, our findings highlight MCO-5 h as a promising electrode for energy storage applications.

Enhanced ferromagnetic properties achieved by F-doping in BaFe1-xMnxO3-δ.

Tailoring the crystal structure, spin, and charge state of perovskite oxides through fluorine ion doping is an attractive and effective strategy, which could significantly modify the physical and chemical properties of base oxides. Here, BaFe1-xMnxO3-δ (x = 0, 0.1, 0.2, 0.3) and BaFe1-xMnxO2.9-δF0.1 (x = 0.1, 0.2, 0.3), belonging to 6H-type BaFeO3-δ, are prepared and investigated to evaluate the impact of F- doping. The distortion of crystal structure and the reduced average valence of Mn and Fe confirm the preference for F- substitution in the hexagonal layer, which are found as the key factors for the improved magnetic properties, including ferromagnetic ordering temperature, coercive force, and remanent magnetization. Moreover, the valence reduction of B-site ions and the increased resistance distinctly indicate the expense of electron hole via fluorine doping. This work describes the adjustment of crystal structure, electronic configuration, and ferromagnetic performance by simple F- doping, which provides a prospect for practical magnetic materials.

Topological edge and corner states of valley photonic crystals with zipper-like boundary conditions

We present a stable valley photonic crystal (VPC) unit cell with C 3v symmetric quasi-ring-shaped dielectric columns and realize its topological phase transition by breaking mirror symmetry. Based on this unit cell structure, topological edge states (TESs) and topological corner states (TCSs) are realized. We obtain a new type of wave transmission mode based on photonic crystal zipper-like boundaries and apply it to a beam splitter assembled from rectangular photonic crystals (PCs). The constructed beam splitter structure is compact and possesses frequency separation functions. In addition, we construct a box-shaped triangular PC structures with zipper-like boundaries and discover phenomena of TCSs in the corners, comparing its corner states with those formed by other boundaries. Based on this, we explore the regularities of the electric field patterns of TESs and TCSs, explain the connection between the characteristic frequencies and locality of TCSs, which helps better control photons and ensures low power consumption of the system.

Photonic antichiral edge states induced by magnetic surface plasmon resonance

Chiral edge states are a hallmark feature of photonic Chern insulators, where waves propagate in opposite directions along two parallel edges of a strip sample. Different from the chiral edge states, at recently discovered counterintuitive antichiral edge states, where waves propagate in the same direction on the two edges, the antichiral edge states are modeled by the modified Haldane model. Here, we theoretically propose, experimentally observe the antichiral edge states induced by magnetic surface plasmon resonance, and realize the antichiral edge states in a gyromagnetic photonic crystal with rectangular lattice. Through microwave experiments and photonic band calculations, the unique properties of this antichiral edge states have been confirmed, including edge dispersion without Dirac points frequencies shift, unidirectional transmission without ancillary cladding, and the operating frequency of the edge states that can be flexibly controlled by the external magnetic field. These results extend the scope of antichiral edge states and supplement the current understanding of antichiral edge states.