Complex Band Research Articles

Electronic spin susceptibility in metallic strontium titanate

Metallic strontium titanate (SrTiO3) is known to have both normal-state and superconducting properties that strongly vary over a wide range of charge carrier densities, but the complex interplay between lattice and electronic degrees of freedom has hindered the development of a clear qualitative description of the observed behavior. A major challenge is to understand how the charge carriers themselves evolve with doping and temperature, with possible polaronic effects and evidence of an effective mass that strongly increases with temperature. Here we use 47,49Ti nuclear magnetic resonance (NMR) to perform a comprehensive study of the electronic spin susceptibility in the metallic state of strontium titanate across the doping-temperature phase diagram. We find a temperature-dependent Knight shift that can be quantitatively understood within a nondegenerate Fermi gas model that fully takes into account the complex band structure of SrTiO3. Our data are consistent with a temperature-independent effective mass, and we show that the behavior of the spin susceptibility is universal in a wide range of temperatures and carrier concentrations. These results provide a microscopic foundation for the understanding of the properties of the unconventional low-density metallic state in strontium titanate and related materials.

Guided ad infinitum assembly of mixed-metal oxide arrays from a liquid metal.

Bottom-up nano- to micro-fabrication is crucial in modern electronics and optics. Conventional multi-scale array fabrication techniques, however, are facing challenges in reconciling the contradiction between the pursuit of better device performance and lowering the fabrication cost and/or energy consumption. Here, we introduce a facile mixed-metal array fabrication method based on guided self-assembly of polymerizing organometallic adducts derived from the passivating oxides of a ternary liquid metal to create mixed metal wires. Driven by capillary action and evaporation-driven Marangoni convection, large-area, high-quality organometallic nano- to micro-wire arrays were fabricated. Calcination converts the organometallics into oxides (semiconductors) without compromising wire continuity or array periodicity. Exploiting capillary bridges on a preceding layer, hierarchical arrays were made. Similarly, exploiting the conformity of the liquid to the mold, arrays with complex geometries were made. Given the periodicity and high refractive index of these arrays, we observe guided mode resonance while their complex band structures enable fabrication of diodes or gates. This work demonstrates a simple, affordable approach to opto-electronics based on self-assembling arrays.

Formulation of the extended plane wave expansion for in‐plane and out‐of‐plane vibrations in viscoelastic phononic thin plates under a constant temperature field

AbstractIn this study, we develop an extended plane wave expansion method to determine the complex elastic band gaps for both in‐plane and out‐of‐plane vibrations in a viscoelastic phononic crystal (PnC) thin plate model under a constant temperature field. The periodic structure of the thin plate comprises a unit cell (UC) consisting of an epoxy matrix and circular steel inclusions. In this configuration, we consider the viscoelastic effects described by the generalized Maxwell model arising from the epoxy matrix. Furthermore, we incorporate thermal effects in the UC, accounting for the linear dependence of the Young's modulus on the temperature of the epoxy matrix, assuming the absence of heat flow in the dimensions of the UC. We present a band structure illustrating the displacement of the real and imaginary parts of the complex band structure for evanescent waves arising from the viscoelastic PnC thin plate, considering both in‐plane and out‐of‐plane vibrations.

In situ electrosynthesis, optimization and stability of AgNPs within chitosan: pullulan polymeric network

Abstract In this study, a systematic investigation to achieve a deeper understanding of the synergistic effect of chitosan (CS) and pullulan (PL) as a polymeric matrix on the in situ electrosynthesis AgNPs under applied voltage 1.5 V for 2 h. The process was applied using CS: PL blend with different ratio as electrolytic solution, reducing, and stabilizing agent avoiding using toxic reducing agent, byproduct of the reaction, controlling AgNPs size and stability. Investigation of the samples using UV–visible spectroscopy (UV–vis), Inductively coupled plasma optical emission spectroscopy (ICP), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS) and Thermogravimetric analysis (TG) revealed that AgNPs successfully formed under controlling the size and stability. Across all ratios except using only PL as an electrolyte, the results revealed the occurrence [chitosan/pullulan] Ag+ complex band at around 250 nm and a localized peak at 420 nm attributed to the SPR of AgNPs. TEM confirmed AgNPs formation with decreasing in size and increasing in concentration as a function of increasing CS content. Findings obtained by quantifying the concentration of silver using ICP whereas the concentration of CS is raised, the concentration of silver liberated increases. Zeta potential revealed that AgNPs have a positive surface charge maximized with increasing CS content. Furthermore, stability against aging for 2 months at 4o C revealed that the addition of PL to CS matrix works on increasing the stability of AgNPs against aging.

Synthesis and Study of Oxide Semiconductor Nanoheterostructures in SiO2/Si Track Template

In this study, chemical deposition was used to synthesize structures of Ga2O3 -NW/SiO2/Si (NW—nanowire) at 348 K and SnO2-NW/SiO2/Si at 323 K in track templates SiO2/Si (either n- or p-type). The resulting crystalline nanowires were δ-Ga2O3 and orthorhombic SnO2. Computer modeling of the delta phase of gallium oxide yielded a lattice parameter of a = 9.287 Å, which closely matched the experimental range of 9.83–10.03 Å. The bandgap is indirect with an Eg = 5.5 eV. The photoluminescence spectra of both nanostructures exhibited a complex band when excited by light with λ = 5.16 eV, dominated by luminescence from vacancy-type defects. The current–voltage characteristics of δ-Ga2O3 NW/SiO2/Si-p showed one-way conductivity. This structure could be advantageous in devices where a reverse current is undesirable. The p-n junction with a complex structure was formed. This junction consists of a polycrystalline nanowire base exhibiting n-type conductivity and a monocrystalline Si substrate with p-type conductivity. The I–V characteristics of SnO2-NW/SiO2/Si suggested near-metallic conductivity due to the presence of metallic tin.

Analysis of band structures using ω(k)- and k(ω)-approaches for two-dimensional truss metamaterials under residual strain and variations in mass distribution

Metamaterials are part of the expanding field of composite materials with engineered structures, though some areas remain underdeveloped. One of these involves the analysis of complex band structures ( k ( ω ) -approach), more particularly to truss cells, in comparison to purely real ones ( ω ( k ) -approach). We seek to fill this knowledge gap by presenting and discussing the employment of both approaches on truss cells, while analyzing how stiffness and mass impact the band structure. Two-dimensional truss metamaterial cells, addressing distinct band gap (BG) phenomena and with real band structure already described in the literature, are evaluated under varying conditions of residual strain and mass distribution between nodes and elements. It is demonstrated that these varying conditions modify band characteristics, with changes in frequency range and attenuation behavior based on the cell type and BG generation phenomenon. These changes are also related to the merging of BGs for two, or even three, distinct or equal phenomena. The study also examines how increasing mass in the elements weakens the association between natural frequencies with BG range and resonant modes, leading to the reduction of distinguishing features. Additional observations from the literature on the expected behavior of the band structure are verified and discussed.

Automatic extraction of fine structural information in angle-resolved photoemission spectroscopy by multi-stage clustering algorithm

Unsupervised clustering method has shown strong capabilities in automatically categorizing the ARPES (ARPES: angle-resolved photoemission spectroscopy) spatial mapping dataset. However, there is still room for improvement in distinguishing subtle differences caused by different layers and substrates. Here, we propose a method called Multi-Stage Clustering Algorithm (MSCA). Using the K-means clustering results/metrics for real space in different energy-momentum windows as the input of the second round K-means clustering for momentum space, the energy-momentum windows that exhibit subtle inhomogeneity in real space will be highlighted. It recognizes different types of electronic structures both in real space and momentum space in spatially resolved ARPES dataset. This method can be used to capture the areas of interest, and is especially suitable for samples with complex band dispersions, and can be a practical tool to any high dimensional scientific data analysis.

Prrx2, the paired-related homeobox transcription factor, functions as a potential regulator of pannexin 3 expression in odontoblast differentiation.

This study aimed to elucidate the roles of Prrx1 and Prrx2, homeobox transcription factors, in tooth development and determine whether Prrx2 regulates pannexin 3 (Panx3) expression, which is important in preodontoblasts. Tooth sections were prepared from 13.5-, 15.5-, and 18.5-day-old embryonic ICR mice, and Prrx1- and Prrx2-expressing cells were identified by in situ hybridization. To clarify the direct relationship between Prrx2 and Panx3, dual-luciferase reporter assay and electrophoretic mobility shift assay (EMSA) were performed. The effect of endogenous Prrx2 suppression on Panx3 expression was analyzed using an siRNA assay. In situ hybridization revealed that in the molars, Prrx1 and Prrx2 were similarly expressed in the bud and cap stages; however, only Prrx2 was expressed in preodontoblasts at the bell stage. In the incisors, Prrx2-expressing cells were observed from dental papilla cells to preodontoblasts. In serial sections, Prrx2-expressing cells in preodontoblasts corresponded to Panx3-expressing cells. Luciferase reporter assay using luciferase reporter plasmids containing Panx3 promoter revealed that Prrx2 overexpression in HEK293 cells significantly increased luciferase activity. EMSA of nuclear extract proteins from Prrx2-overexpressing HEK293 cells or mouse dental papilla-derived cells to the Panx3 promoter showed the protein-probe complex bands. SiRNA assay revealed that Prrx2 knockdown inhibited Panx3 expression. Our results suggest that Prrx2 may regulate Panx3 expression during odontoblastic differentiation.

Flexoelectric effect on bandgap properties of periodic bi-directional-graded curved nanoshells

With the miniaturization of devices, the size effect of structures becomes increasingly apparent and it becomes crucial to consider flexoelectricity in MEMS/NEMS. Given that functionally graded materials (FGMs) can generate strain gradients that enhance flexoelectricity, it is both novel and crucial to investigate the synergistic effects of FGMs and flexoelectricity on bandgap characteristics. Understanding these interactions is essential for advancing materials science and could lead to significant innovations in nanotechnology. In this work, a theorectical model for the periodic flexoelectric doubly-curved nanoshells with bi-directional functionally graded(BDFG) and porosity considered are constructed. As the governing equations for longitudinal FG problems are more difficult to be solved analytically, their precise analysis is more challenging. Thus, an improved transfer matrix method based on state-space is proposed innovatively to obtain the complex band structures for longitudinal FG problems. Subsequently, the influences of the flexoelectric effect, strain gradient effect, BDFG indices, and porosity distributions on bandgaps are systematically discussed. The results indicate that the flexoelectric effect is non-negligible at small scales, which generally widens the bandgaps, with higher frequency ranges and larger attenuation capacity. Bandgaps are sensitive to the variation of functionally graded indices. Particularly, flexoelectricity brings about the appearance and disappearance of some bandgaps during the variation of FG index in the thickness direction n3, and complicates the bandgaps variation. Besides, the porosity distribution patterns and porosity coefficients enrich the regulation of bandgaps. Our investigation offers valuable insights into the application of flexoelectric electrical components combined with BDFG in MEMS/NEMS to the wave propagation domain.

A computational study of AlScN-based ferroelectric tunnel junction

Ferroelectric (FE) AlScN materials have been experimentally explored for memory and neuromorphic computing device applications. Here a computational study is performed to simulate the device characteristics and assess the performance potential of a ferroelectric tunnel junction (FTJ) based on AlScN. We parameterize an efficient k⋅p Hamiltonian from the complex band structure of AlScN from ab initio density-functional theory calculations to enable efficient quantum transport simulations of the FTJ device. Using a metal–FE–graphene structure enhances the barrier height modulation and the tunneling electroresistance (TER) ratio, compared to a metal–FE–semiconductor FTJ device structure. The barrier height modulation between ON and OFF states can reach ∼ 0.7eV with a FE polarization of 25 μC/cm2. Reducing the AlScN tunnel layer thickness is important for increasing the device ON current and reducing the read latency. The results indicate the importance of contact designs and FE layer thickness in the design of AlScN-based FTJ devices, and highlight the potential of AlScN FTJ for future memory device technology applications.

Subwavelength topological interface modes in a multilayered vibroacoustic metamaterial

We present a systematic and rigorous analytical approach, based on the transfer matrix methodology, to study the existence, evolution, and robustness of subwavelength topological interface states in practical multilayered vibroacoustic phononic lattices. These lattices, composed of membrane-air cavity unit cells, exhibit complex band structures with various bandgaps, including Bragg, band-splitting induced, local resonance, and plasma bandgaps. Focusing on the challenging low-frequency range and assuming axisymmetric modes, we show that topological interface states are confined to Bragg-like band-splitting induced bandgaps. Unlike the Su-Schrieffer-Heeger model, the vibroacoustic lattice exhibits diverse topological phase transitions across infinite bands, enabling broadband, multi-frequency vibroacoustics in the subwavelength regime. We establish three criteria for the existence of these states: the Zak phase, surface impedance, and a new reflection coefficient concept, all derived from transfer matrix components. Notably, we provide an explicit expression for the exact location of topological interface states within the band structure, offering insight for their predictive implementation. We confirm the robustness of these states against structural variations and identify delocalization as bandgaps narrow. Our work provides a complete and exact analytical characterization of topological interface states, demonstrating the effectiveness of the transfer matrix method. Beyond its analytical depth, our approach provides a useful framework and design tool for topological phononic lattices, advancing applications such as efficient sound filters, waveguides, noise control, and acoustic sensors in the subwavelength regime. Its versatility extends beyond the vibroacoustic systems, encompassing a broader range of phononic and photonic crystals with repetitive inversion-symmetric unit cells.

Mechanochemical synthesis of FeCo nanoalloys

The Iron-Cobalt Nanoalloys (ICNAs) were synthesized by co-reduction of the mixture of FeCl2.4H2O and CoCl2.6H2O salts and also in the chemical reduction of iron(II) bis(oxalate)cobaltate pentahydrate complex by aluminum nanoparticles in the solid-state at room temperature. Aluminum nanoparticles were prepared by a novel wire drawing method in the presence of lubricating oil. The products were characterized by IR, XRD, FESEM, EDX and VSM. The absorption bands do not appeared in FTIR spectra of FeCo nanoalloys (ICNAs) while, the spectra of precursor show all the absorption bands of the corresponding complex and salts. The X-ray diffraction pattern results show the presence of two phases unreacted aluminum and FeCo in ICNAs. The weight fraction of FeCo nanoparticles are calculated by the Rietveld method. Quantitative XRD analysis of FeCo-Al (S1) shows a weight fraction of 89.82 % FeCo and unreacted aluminum 10.18 % also, calculation in FeCo-Al (S2) shows weight fraction FeCo and unreacted aluminum 78.50 and 21.50 % respectively. FESEM image of S1 and S2 show maximum particles size distribution in the region of 60 nm to 100 nm and 40 nm to 80 nm respctively. The hysteresis loop of S1 and S2 show magnetic saturation 101.8900 emu/g and 39.6442 emu/g respectively.

Complex band structure of two-dimensional thermal wave crystals

We investigate the complex band structure of temperature oscillations in a two-dimensional thermal wave crystal. We use the Cattaneo-Vernotte heat model to describe the thermal properties. We apply the plane wave method to calculate the complex band structure of a square lattice composed of an infinite array of square bars. We find that a complete band gap exists across the whole Brillouin zone, where temperature oscillations are forbidden. This has potential applications in thermal management, thermal cloaking, and other areas.

Study on the feasibility of distinguishing ventricular and pre-excited arrhythmia rhythms by a new algorithm

BackgroundThe differentiation and diagnosis of ventricular tachycardia (VT) and pre-excited tachycardia (PXT) remains a challenging task, especially when typical AV dissociation is not present. The purpose of this article is to study the feasibility of a new theoretical algorithm for identifying ventricular arrhythmias (VA) and pre-excited arrhythmias (PA) rhythms (which can be used to distinguish VT from PXT, etc.). MethodThis study involved the deduction of a new algorithm by combining knowledge of cardiac anatomy, vectorcardiography, and cardiac electrophysiology. The new algorithm evaluated the diagnostic value through intracardiac electrophysiology in 205 cases of VA and PA. The new algorithm diagnoses VA based on the following 4-step process:1.The QRS complex in leads II, III, and aVF shows a unidirectional R wave, and lead aVR shows a QS pattern.2.S waves are predominant in two or more of leads I, aVF, and V6.3.Lead V2 shows ≥3 phase waves or returning branch notching (note: returning branch refers to the band of QRS complexes returning to the baseline).4.Lead V5 shows a negative wave in the initial portion or returning branch notching.If none of these criteria are met, the diagnosis is PA. The diagnostic value of the new algorithm is compared with the Steurer algorithm and the Vereckei algorithm (diagnosed based on the QRS waveform characteristics of the two algorithms during electrophysiological verification, excluding the diagnosis of atrioventricular dissociation). ResultsThe new algorithm showed significant advantages in terms of AUC value (0.83 vs. 0.61 vs. 0.57), sensitivity (83.6 % vs. 23.3 % vs. 24.8 %), and accuracy (82.9 % vs. 48.3 % vs. 46.3 %) compared to the Steurer algorithm and Vereckei algorithm based on QRS waveform characteristics for diagnosing VA (137 cases) and PA (68 cases). This indicates that the new algorithm is more accurate in identifying idiopathic VA. While there was a significant difference in specificity between the New algorithm and Steurer algorithm (82.3 % vs. 98.5 %, p < 0.05), the difference with Vereckei algorithm (82.3 % vs. 89.7 %) was not significant.In the New algorithm, the sensitivity and specificity for each step are as follows:-Step 1: Sensitivity 34.3 %, Specificity 94.1 %.-Step 2: Sensitivity 24.1 %, Specificity 98.5 %.-Step 3: Sensitivity 18.3 %, Specificity 100 %.-Step 4: Sensitivity 6.6 %, Specificity 89.7 %.Step 1 had the highest AUC value, indicating the best overall diagnostic performance among all steps. Step 2 and Step 3 also performed well, while Step 4 had relatively poorer diagnostic performance. ConclusionThe new algorithm is suitable for identifying the origin of VA and PA rhythms.

Attenuation of Lamb waves in coupled-resonator viscoelastic waveguide

Guidance of elastic waves is one of the main applications of artificial crystal structures. The attenuation of the guided waves is, however, often overlooked, as most of the proposed waveguides only comprise ideal elastic materials. In this work, we study the propagation of evanescent Lamb waves guided in coupled-resonator viscoelastic waveguide (CRVW), with special attention to attenuation. CRVW is defined by considering a linear chain of coupled defect cavities in a phononic plate made of epoxy. The viscoelastic behavior of epoxy is characterized numerically by the Kelvin–Voigt (K–V) model. Based on finite element analysis, the complex band structure and the spectrum of frequency response function (FRF) are obtained. Due to viscosity, guided Lamb waves are spatially damped. Two theoretical models are devised to predict the displacement distributions inside and outside a bandgap for guided waves, respectively, considering either the first or the first two least evanescent Bloch waves identified in the complex band structure. A CRVW sample is fabricated and characterized experimentally by laser vibrometry. Evanescent Lamb waves are observed to be strongly confined along the waveguide and at the same time to decay rapidly along the waveguide axis. Experiments and numerical simulations are found to be in fair agreement. The present work is expected to inspire practical applications of highly confined viscoelastic phononic waveguides.

Monitoring Binding of Protamine with DNA Using Protein Charge Transfer Spectra.

In this work, novel intrinsic electronic absorption (250-400 nm) with a molar extinction coefficient of 752 M-1cm-1 at 250 nm, arising from photoinduced electron transfer involving charged amino acid side chains and the polypeptide backbone, along with luminescence (300-500 nm) with quantum yield of 0.011 from subsequent charge recombination, was observed in salmon sperm Protamine (PRM). The absorption of PRM was attributed to the previously identified Peptide Backbone-to-Side chain Charge Transfer (PBS-CT) from the polypeptide backbone to the abundant cationic headgroups of Arginine in PRM, while the luminescence was believed to originate from charge recombination within the charge-separated excited states of PRM. Remarkably, since Arg is the only charged residue in the PRM sequence, the PRM Protein Charge Transfer Spectra (ProCharTS) is both totally and uniquely Arg specific. Interestingly, the peak of PRM luminescence emission spectrum was independent of the excitation wavelength, unlike other proteins such as human serum albumin, displaying unconventional luminescence. Aggregation-induced effects on PRM absorbance and luminescence were ruled out, as both PRM absorbance and luminescence increase maintained linearity with increasing concentration in the 25-150 μM range. Nucleoprotamine complex formation, resulting from the binding of PRM with calf-thymus genomic DNA (gDNA), was monitored through increased scattering by the nucleoprotamine complex, a decrease in gDNA/PRM absorbance, a decrease in gDNA/PRM ellipticity, and shifts of nucleoprotamine complex band upon agarose gel electrophoresis. Upon binding with gDNA (700 μM base pair concentration), PRM ProCharTS absorbance at 260 nm decreased by 72%. This decrease was attributed to the formation and subsequent precipitation of nucleoprotamine complex upon PRM-gDNA binding. The application of ProCharTS absorbance to indirectly monitor DNA-protein binding in a label-free approach was thus demonstrated.

On the use of complex band structure to study valley photovoltaics: toward efficient hot carrier extraction

On the use of complex band structure to study valley photovoltaics: toward efficient hot carrier extraction

A zero-dimensional 1-butylpiperazine-cadmium(II) hybrid material: Synthesis, structural analysis, and DFT studies

This study reports the synthesis and characterization of an organoammonium-cadmium(II) hybrid material, (BPH₂)₂[Cd₂Cl₈] (BP = 1-butylpiperazine), using a combination of experimental and theoretical techniques. Single-crystal X-ray diffraction shows a centrosymmetric crystal structure in the P1¯ space group, featuring a zero-dimensional (0D) arrangement where binuclear [Cd₂Cl₈]⁴⁻ anions and (C₈H₂₀N₂⁺) cations are linked by N—H···Cl and C—H···Cl hydrogen bonds. Hirshfeld surface analysis further elucidates these intermolecular noncovalent interactions, highlighting the dominant role of H···Cl contacts in the molecular packing. The crystal morphology is further investigated via the Bravais-Friedel-Donnay-Harker (BFDH) model. Infrared (IR) spectroscopic analysis was conducted to identify vibrational modes, confirm structure, and elucidate bonding features. Additionally, Experimental UV–visible study indicates an optical band gap energy of 4.75 eV, and density functional theory (DFT) calculations corroborate these findings, predicting a direct band gap of 4.45 eV. Moreover, theoretical calculations, including the complex dielectric function, band structure, and total density of states (DOS), were performed to explore the electrical and optical properties. Finally, the chemical reactivity was evaluated using conceptual-DFT descriptors at the B3LYP/SDD/aug-cc-pVTZ level of theory.

Interplay of Circularly Polarized Light with Molecular and Structural Chirality: Chiral Lanthanide Complexes and Cellulose Nanocrystals

AbstractThe interaction of circularly polarized (CP) light with chiral matter at different scales opens several possibilities of light manipulation in photonic and electronic devices. Here it is shown that in a multilayer architecture, it is possible to take advantage of the polarization‐selective reflection of the nematic arrangement of cellulose nanocrystals and the strong intrinsic CP luminescence (CPL) of the various bands of chiral Eu complexes. In this way, both the intrinsic CPL and total emission of the complex are modified depending on the enantiomer applied and on the detection geometry. This concept may apply for polarization control in electronic and photonic devices and polarized optical cavities.

Complex dispersion analysis of viscoelastic effects on elastic waves in three-dimensional single-phase metamaterials

In this paper, we study the propagation of elastic waves in three-dimensional single-phase metamaterials using the finite element method. Both elastic and viscoelastic scenarios are considered, where the Kelvin-Voigt model is used to describe the solid material viscosity. We explore the influence of material viscosity on the complex band diagrams and the transmission spectra in detail. It is found that the single-phase metamaterials support both the Bragg scattering and locally resonant band gaps. When a small viscosity is introduced, the wave attenuation within the locally resonant band gaps degrades. However, such a small viscosity has negligible effects on the Bragg scattering band gaps. As the material viscosity increases, the wave attenuation is mainly ascribed to the material viscosity rather than the band gap effects. Additionally, the attenuation behavior of evanescent waves can be accurately predicted from the imaginary part of wave vectors identified in the complex band structures. This work provides a reference for the practical applications of viscoelastic metamaterials.