Density Of The States Research Articles

Tuning the soft bandgap in the density of the states: the measurement of a "magnetogap" effect in carbon-black samples

We investigated the magnetic field dependence on the variable range hopping electron conduction in carbon-black samples with different volumetric densities. By applying the concepts and equations of hopping regimes when the magnetic field is applied, we were able to establish a connection between the variation of the hopping temperatures, TES and TM, with the localization radius of electron conduction in carbon-black, as well as with the density of states of this material. The volumetric density dependence of all these physical quantities is also discussed. Finally, based on the magnetic field effects on the hopping parameters, we introduced the idea of a "Magnetogap" effect, indicating how the Coulomb gap changes with the magnetic field.

Disparities in Multiple Myeloma Mortality Rate Trends by Demographic Status in the USA.

Multiple myeloma (MM) is a hematological malignancy that arises when plasma cells undergo malignant monoclonal proliferation. This study aimed to assess the demographic disparities and temporal trends in the mortality rates of this disease. We employed the Center for Disease Control and Prevention's Wide-ranging ONline Data for Epidemiologic Research (CDC WONDER) database. We found that for the overall U.S. population, the age-adjusted mortality rate per 1,000,000 (AAMR) decreased from 1999 to 2020. However, rates differed between demographic groups. In addition, we sought to find a significant average annual percent change (AAPC) in mortality rate from 1999 to 2020 for various demographic populations and compared groups to find disparities in mortality rate trend. In 2020, the AAMR due to MM was 38.0 and for women 24.1. The AAPC in AAMR from 1999 to 2020 in men was -1.0% (95%CI=-1.3 to -0.7) and in women was -1.6% (95%CI=-1.6 to -2.3). A significant difference in trend by sex was found, where women had a higher rate of decline. In 2020, the AAMR for the American Indian or Alaska Native (AI/AN) population was 15.0, the Asian American and Pacific Islander (AAPI) had 14.8, the Black and African American population had an AAMR of 55.6 and the White population had an AAMR of 28.1. The AAPC for the AI/AN population was -2.2% (95%CI=-3.5 to -0.9), for the AAPI population it was -0.9% (95%CI=-1.5 to -0.4), the Black and African American population had -1.5% (95%CI=-2.2 to -0.8) and the AAPC for the White population was -1.1% (95%CI=-1.6 to -0.6). A significant difference in trend of decline was found between the AAPI and Black and African American populations and between the AI/AN and Black and African American populations. When assessing the U.S. by states, the mid-southeast U.S. had the greatest density of the states with high AAMRs. These findings suggest which populations are at increased risk for mortality due to multiple myeloma and where we should apply additional resources and research.

The Adsorption Behavior of Hydrogen on the PuO2(111) Surface: A DFT+U Study

Based on density functional theory, a first-principles study of the adsorption behavior of hydrogen atoms on the PuO2(111) surface is carried out in this work. Models for three different surface morphologies of PuO2(111) are established. It is found that the surface with the outermost oxygen atom (sub outer Pu atom) morphology has the best stability. Based on this model, the adsorption energy, bader charge, and electronic density of the states of a hydrogen atom at different adsorption sites are calculated. Finally, we analyzed the process of hydrogen dissociation into hydrogen atoms on the surface using the cNEB method. The results indicate that the top position of the outermost oxygen atom and the bridge position of the second outermost plutonium atom are relatively stable adsorption configurations, where hydrogen atoms lose electrons and release heat, forming O-H bonds with oxygen atoms. The density of states of O-p orbital electrons will undergo significant changes, reflecting the hybridization of O-p and H-s orbital electrons, forming a stable bonding effect. The dissociation of hydrogen molecules into two hydrogen atoms adsorbed on the top of oxygen atoms requires crossing an energy barrier of 1.06 eV. The decrease in total energy indicates that hydrogen tends to exist on the PuO2(111) surface in a hydrogen atom state. The research results lay the foundation for theoretically exploring the hydrogenation corrosion mechanism of the PuO2(111) surface, providing theoretical support for exploring the corrosion aging of plutonium oxide, predicting the material properties of plutonium oxide under extreme and special environments.

Thermophase Seebeck Coefficient in Hybridized Superconductor-Quantum-Dot-Superconductor Josephson Junction Side-Coupled to Majorana Nanowire.

The dc Josephson current is generated from phase difference between two superconductors separated by a mesoscopic thin film (Josephson junction) without external bias voltage. In the presence of a temperature gradient across the superconductors, a thermal phase is induced under the condition of open circuit. This is very similar to the Seebeck effect in the usual thermoelectric effect, and the thermal phase is thus named as thermophase Seebeck coefficient (TPSC). Here we find obvious enhancement and sign change of the TPSC unique to the Josephson junction composing of two superconductors connected to a semiconductor quantum dot (QD), which is additionally side-coupled to a nanowire hosting Majorana bound states (MBSs), the system denoted by S-MQD-S. These result arise from the newly developed states near the Fermi level of the superconductors due to the QD-MBS hybridization when the dot level is within the superconducting gap. The sign change of the TPSC provides a strong evidence of the existence of MBSs, and is absent if the QD is coupled to regular fermion, such as another QD (system denoted by S-DQD-S). We show that the magnitude and sign of the TPSC are sensitive to the physical quantities including interaction strength between the QD and MBSs, direct overlap between the MBSs, system equilibrium temperature, as well as hopping amplitude between the QD and the superconductors. The obtained results are explained with the help of the current-carrying density of the states (CCDOS), and may be useful in interdisciplinary research areas of Josephson and Majorana physics.

DFT studies of the borophene basic optoelectronic properties doped with aluminum and gallium substitutional atoms

Currently, two-dimensional materials are widely studied from both theoretical and experimental points of view. Among a large list of systems, one finds a two-dimensional boron allotrope (borophene), which has attracted considerable attention due to its promising electronic and optical properties. Understanding and modifying these properties are crucial for implementation of borophene in high-technological applications, but for this to be possible we need to know its very basic physical properties. Therefore, in this work we study borophene that belongs to the P-mmm phase group via first principles to examine the variation of the optoelectronic properties of a pristine borophene monolayer, and the one with Al and Ga substitutional impurities. We report the band structure with the correspondingly density of the states for the pristine system as well as for the doped borophene one. We do reproduce the optical conductivity for the pristine borophene obtained from the complex dielectric function considering several values of the scattering time parameter (τ) of Drude-like model. In addition, here we report the effect of the impurities on the optical conductivity, with the same set of τ parameters, as well as the absorption coefficient with x- and y-polarized incident light. We have found that impurities significantly modify the optical conductivity, but, most importantly, this also enhances the absorption coefficient in the visible region of the electromagnetic spectrum.

Effects of Co-Addition of Guanidinium and Cesium to CH3NH3PbI3 Perovskite Solar Cells

The effects of guanidinium (C(NH2)3, GA) and cesium (Cs) co-additions on methylammonium lead iodide (CH3NH3PbI3, MAPbI3) perovskite solar cells were investigated. The first-principles calculations on the density of the states and band structures showed a reduction in the total energy by the GA addition. Although the calculation showed that the co-addition of the GA/Cs to the MAPbI3 perovskite could decrease the carrier mobilities, and the addition of GA/Cs improved the device performance. This result would be due to a facilitation of grain growth and a suppression of the defects from the GA/Cs addition. The changes to the conversion efficiencies of the device with the best performance were small, which indicates that the present co-addition of GA/Cs is effective for the stability of the devices.

Development of diagnostics of electron density and temperature for atmospheric-pressure helium plasma based on optical emission spectroscopy analysis and a collisional-radiative model

An algorithm for diagnosing the electron density and temperature of helium plasma at atmospheric pressure has been developed based on a revised helium collisional-radiative (CR) model. Atomic collision processes are included, and part of the atomic data of electron collision processes in the conventional CR model has been updated to expand its valid pressure. The algorithm uses eight emission lines in the visible-wavelength range as inputs to determine the electron density, electron temperature, and number density of the two metastable states by fitting the number density of the states corresponding to the emission lines. The algorithm has a considerably small theoretical error. In the microwave-discharged low-pressure helium plasma experiment, the results obtained with the algorithm agreed well with the results obtained with the probe method. The electron density and temperature of the atmospheric-pressure helium plasma obtained with the algorithm agreed well with the results of the continuum spectrum analysis.

Determining the Height of Energy Barriers of the Cyclohexene Molecule Using Stochastic Approximation

The Monte Carlo method (stochastic approximation) is used for calculating the relative values of density of the states of the cyclohexene molecule in the space of Cremer–Pople coordinates. Using this data, the heights of the energy barriers separating the molecule stereoisomers are estimated.

Structural, Spectroscopic, Electric and Magnetic Properties of New Trigonal K5FeHf(MoO4)6 Orthomolybdate

A new multicationic structurally disordered K5FeHf(MoO4)6 crystal belonging to the molybdate family is synthesized by the two-stage solid state reaction method. The characterization of the electronic and vibrational properties of the K5FeHf(MoO4)6 was performed using density functional theory calculations, group theory, Raman and infrared spectroscopy. The vibrational spectra are dominated by vibrations of the MoO4 tetrahedra, while the lattice modes are observed in a low-wavenumber part of the spectra. The experimental gap in the phonon spectra between 450 and 700 cm-1 is in a good agreement with the simulated phonon density of the states. K5FeHf(MoO4)6 is a paramagnetic down to 4.2 K. The negative Curie-Weiss temperature of -6.7 K indicates dominant antiferromagnetic interactions in the compound. The direct and indirect optical bandgaps of K5FeHf(MoO4)6 are 2.97 and 3.21 eV, respectively. The K5FeHf(MoO4)6 bandgap narrowing, with respect to the variety of known molybdates and the ab initio calculations, is explained by the presence of Mott-Hubbard optical excitation in the system of Fe3+ ions.

Theoretical exploration of inherent electronic, structural, mechanical, thermoelectric, and thermophysical response of KRu4Z12 (Z = As12, Sb12) filled skutterudite materials.

Using the density functional theory methodology, we have thoroughly examined KRu4As12 and KRu4Sb12 skutterudites, including their structural, electronic, mechanical, transport, and thermodynamic properties. First and foremost, using the Birch-Murnaghan equation of state, the structural stability has been calculated in terms of their total ground state and cohesive energies. With the use of the approximation approaches GGA and GGA + mBJ, the electrical structure and density of the states reveal their metallic nature. This demonstration predicts the dominant ferromagnetic spin configuration of materials by considering their electronic behavior and magnetic interactions. The ductile behavior of these alloys is also addressed by their mechanical qualities, which indicate how they might be used in engineering and industrial settings. Moreover, the semi-classical Boltzmann transport theory has been employed to examine the Seebeck coefficient as well as the electric and thermal conductivities. The general tendency of these compounds demonstrates their various potential uses as electrode materials. The quasi-harmonic Debye approximation is a method used to analyze the stability of a system under high pressures and accounts for the temperature dependency of thermodynamics. It combines the quasi-harmonic approximation, which considers the anharmonicity of vibrations, with the Debye model, which describes the vibrational modes of a solid. This approach allows for a more accurate representation of the system's behavior at different temperatures and pressures. By implementing this approximation, researchers can gain insights into the stability and thermodynamic properties of materials under extreme conditions.

In English

An influence of the adsorbed molecules layer on the optical characteristics of the spherical metallic nanoparticles has been studied in the work. In order to do this one considers the additional term which takes into account the scattering of electrons at the interface between metal and adsorbate. The analytical expressions for the frequency dependences for the parameter of coherence loss due to the scattering at the interface “metal – adsorbed layer” have been obtained. It has been found that the presence of the adsorbed molecules results in the electron scattering anisotropy, and, hence, in the anisotropy of the optic response of such systems. The result of the indicated anisotropy is the appearance of the additional maximum in the infrared part of the spectrum in the frequency dependences for the optical characteristics. An evolution of the frequency dependences for the components of the polarizability tensor and the absorption cross-section and scattering cross-section for the two-layer spherical nanoparticles of the type “metal – adsorbate” under the variation of their geometrical parameters has been analyzed. It has been shown that the weak maximum of the real, imaginary parts and the module of the transverse component of the polarizability tensor and the absorption and scattering cross-sections in the infrared part of the spectrum appears due to inducing of the local density of the states by adsorbate. The reason of the shift of the maxima of the absorption cross-section and scattering cross-section for the nanoparticles of the constant sizes with the cores of different metals has been found. It has been demonstrated the existence of the small-scale oscillations at the frequency dependences for the components of the polarizability tensor and at the absorption and scattering cross-sections, caused by an oscillating contribution of the surface electron scattering. The dependence of the location and the value of the maximum of the absorption cross-section for the particle “metal – adsorbate” with the constant geometrical parameters and content on the dielectric permittivity of the medium, in which the nanoparticle is situated, has been proved.

Investigating the β-Mg17Al12 Alloy under Pressure Using First-Principles Methods: Structure, Elastic Properties, and Mechanical Properties

Calculations of first principles were employed to explore the elastic constants of the β-Mg17Al12 intermetallic complex under pressure, along with several related physical parameters, including the bulk modulus, the shear modulus, Young’s modulus, Poisson’s ratio, and the anisotropy index. The volume of the β-Mg17Al12 crystal in the ground state was V0 = 1180.353 Å3, and the lattice parameter was 10.57 Å. This is in agreement with the available results in the literature, which indicate that the calculations were correct. The three independent elastic constants, C11, C12, and C44, increased with increasing pressure. The bulk modulus B, shear modulus G, and Young’s modulus E increased with increasing pressure, indicating that the bulk deformation resistance, shear deformation resistance, and stiffness of the β-Mg17Al12 phase increased with increasing pressure. The phase had a B/G > 1.75 and a Poisson’s ratio of ν > 0.26 and increased with pressure, indicating that the β-Mg17Al12 crystals were ductile and that the ductility increased with pressure. The Cauchy pressure C12–C44 increased with increasing pressure. The anisotropy coefficients A(100) and A(110) deviated further from 1, and the anisotropy increased. The electronic structure calculations showed that the total density of the states (TDOS) was achieved mainly by the Mg-3p and Al-3p states, and the total density of states moved toward the higher energy regions under pressure, with enhanced interatomic bonding, leading to an increase in the elastic constants and ultimately to an increase in each physical property with increasing pressure.

Crystal and electronic structures of BiS2 -based compounds Sr0.5X0.5FBiS2 (X=rare earth) under pressure: Correlation with the change in the superconductivity from unconventional to conventional

${\mathrm{Sr}}_{1\ensuremath{-}x}{X}_{x}{\mathrm{FBiS}}_{2}$ $(X:\text{rare earth})$ is considered to show a pressure-induced structural transition around 1 GPa where the superconductivity changes from unconventional in the low-pressure phase to conventional in the high-pressure phase with increasing the superconducting transition temperature (${T}_{c}$). We clarified the monoclinic crystal structure ($P{2}_{1}/m$) in the high-pressure phase which is the same as the high-pressure phase of $X{\mathrm{O}}_{1\ensuremath{-}x}{\mathrm{F}}_{x}\mathrm{Bi}{Y}_{2}$ ($Y$: chalcogen) systems. We performed high-resolution x-ray absorption spectroscopy (XAS) to study the electronic structure of ${\mathrm{Sr}}_{1\ensuremath{-}x}{X}_{x}{\mathrm{FBiS}}_{2}$ systematically, indicating the Bi charge state of nearly $3+$. The pressure dependence of the XAS spectra of ${\mathrm{Sr}}_{0.5}{\mathrm{La}}_{0.5}{\mathrm{FBiS}}_{2}$ and ${\mathrm{Sr}}_{0.5}{\mathrm{Nd}}_{0.5}{\mathrm{FBiS}}_{2}$ indicate a large change in the electronic structure around the structural transition pressure, which corresponded to the transition from semiconductorlike to more metallic states. The increase of the empty states of Bi $s$ and $d$ (${t}_{2g}$) bands above the Fermi level was observed in the high-pressure phase. Density functional theory calculations showed that the density of the states at the Fermi level did not show a significant change in the high-pressure phase, where higher ${T}_{c}$ was observed.

Nonequilibrium dynamics in a spin valve with noncollinear magnetization

We utilize a hybrid quantum-classical equation of motion approach to investigate the spin dynamics and spin-transfer torque in a spin valve under bias voltage. We show that the interplay between localized classical magnetic moments and conduction electrons induces a complex effective exchange coupling between the magnetic layers. This leads to a declination of magnetizations from layers anisotropy axes even in equilibrium. Introducing a finite bias voltage triggers spin currents and related spin-transfer torques which further tilt the magnetizations and govern the relaxation processes of the spin dynamics. Analyzing different scenarios of the applied bias voltage, we show that symmetric and asymmetric voltage drops can lead to relaxation times of the spin dynamics that differ by several orders of magnitude at comparable charge currents. In both cases we observe resonant features, where the relaxation is boosted whenever the chemical potential of the leads matches the maxima in the density of the states of the spin-valve electrons.

Light-Trapping-Enhanced Photodetection in Ge/Si Quantum Dot Photodiodes Containing Microhole Arrays with Different Hole Depths.

Photodetection based on assemblies of quantum dots (QDs) is able to tie the advantages of both the conventional photodetector and unique electronic properties of zero-dimensional structures in an unprecedented way. However, the biggest drawback of QDs is the small absorbance of infrared radiation due to the low density of the states coupled to the dots. In this paper, we report on the Ge/Si QD pin photodiodes integrated with photon-trapping hole array structures of various thicknesses. The aim of this study was to search for the hole array thickness that provided the maximum optical response of the light-trapping Ge/Si QD detectors. With this purpose, the embedded hole arrays were etched to different depths ranging from 100 to 550 nm. By micropatterning Ge/Si QD photodiodes, we were able to redirect normal incident light laterally along the plane of the dots, therefore facilitating the optical conversion of the near-infrared photodetectors due to elongation of the effective absorption length. Compared with the conventional flat photodetector, the responsivity of all microstructured devices had a polarization-independent improvement in the 1.0–1.8-μm wavelength range. The maximum photocurrent enhancement factor (≈50× at 1.7 μm) was achieved when the thickness of the photon-trapping structure reached the depth of the buried QD layers.

Controllable tuning of polymetallic Co-Ni-Ru-S-Se ultrathin nanosheets to boost electrocatalytic oxygen evolution

Replacing precious metals in oxygen evolution reaction (OER) catalysts has broad prospects to achieve a viable water splitting system. Since the electrocatalytic OER is a four-electron transfer reaction with a very sluggish kinetic process, there is great interest in the development of inexpensive, durable, and high-efficiency OER catalysts. Herein, trimetallic Co-Ni-Ru sulfoselenide and bimetallic sulfoselenide nanosheets were designed by regulating their composition and morphology for efficient and durable OER electrocatalysis. The sheet structure has a large specific surface area to promote contact between the catalyst and electrolyte. Compared with bimetallic Co-Ni, Co-Ru, Ni-Ru, Co-Cd, and Co-Au sulfoselenide nanosheets, trimetallic Co-Ni-Ru sulfoselenide nanosheets show superior OER performance. By modulating the composition ratio of metal atoms in the Co-Ni-Ru-S-Se nanosheets (1:1:0.5:1:1), the nanosheets showed a significant OER overpotential of η = 261 mV (1.491 V versus RHE) at 10 mA cm−2, a Tafel slope of 52.2 mV dec–1 and outstanding stability after 48 h of continuous testing. For comparison, Co-Ni, Co-Ru, Ni-Ru, Co-Cd, and Co-Au bimetallic sulfoselenide nanosheets (denoted as Co-Ni-S-Se, Co-Ru-S-Se, Ni-Ru-S-Se, Co-Au-S-Se, Co-Cd-S-Se) were also tested. Density functional theory (DFT) calculations showed that appropriately doping Ru and Ni simultaneously (Co-Ni-Ru-S-Se) can increase the density of the states at the Fermi level, resulting in excellent charge density and low intermediate adsorption energy. These findings present a practical route to design 2D polymetallic nanosheets to optimize catalytic OER performance.

Laughlin topology on fractal lattices without area law entanglement

Laughlin states have recently been constructed on fractal lattices, and the charge and braiding statistics of the quasiholes were used to confirm that these states have Laughlin type topology. Here, we investigate density, correlation, and entanglement properties of the states on a fractal lattice derived from a Sierpinski triangle with the purpose of identifying similarities and differences compared to two-dimensional systems and with the purpose of investigating whether various probes of topology work for fractal lattices. Similarly to two-dimensional systems, we find that the connected particle-particle correlation function decays roughly exponentially with the distance between the lattice sites measured in the two-dimensional plane, but the values also depend on the local environment. Contrary to two-dimensional systems, we find that the entanglement entropy does not follow the area law if one defines the area to be the number of nearest neighbor bonds that cross the edge of the selected subsystem. Considering bipartitions with two bonds crossing the edge, we find a close to logarithmic scaling of the entanglement entropy with the number of sites in the subsystem. This also means that the topological entanglement entropy cannot be extracted using the Kitaev-Preskill or the Levin-Wen methods. Studying the entanglement spectrum for different bipartitions, we find that the number of states below the entanglement gap is robust and the same as for Laughlin states on two-dimensional lattices.

Layered Metallic Vanadium Disulfide for Doubly Q-Switched Tm:YAP Laser with EOM: Experimental and Theoretical Investigations.

In the current study, layered metallic vanadium disulfide (VS2) is fabricated by a liquid-phase exfoliation method, and its microstructures as well as optical characteristics are investigated. Based on first-principles calculations, the band structure and density of the states of both bulk T-VS2 and monolayer H-VS2 are illustrated, showing the metallic behavior with a zero band gap. By using VS2 as the saturable absorber in a doubly Q-switched Tm:YAP laser with an EOM, the Q-switching laser pulses at 2 μm with 22 ns and 200 Hz are generated, corresponding to the single pulse energy of 755 μJ and the peak power of 34.3 kW. The coupled rate equations of the doubly Q-switched laser are given, and the numerical simulations agree with the experimental results. The results indicate that VS2 is a promising nanomaterial due to its nonlinear optical property. The doubly Q-switched laser demonstrates a high level of performance in reducing pulse width and enhancing pulse peak power.

BASIC CONCEPTS IN PSYCHIATRIC GENETICS

We have performed spin-polarized calculation for the electronic band structure, density of states, Fermi surface and the space electronic charge density distribution for the filled-skutterudites LaFe4Pn12 (Pn=P, As and Sb) compounds. It has been noticed that for both LaFe4P12 and LaFe4As12 there are two bands cross Fermi level (EF) for the spin-up and spin-down states, while for LaFe4Sb12 there is only one band cross EF for the spin-up state and three bands cross EF for the spin-down state. As the partial DOS of La-s,d, Fe-s/p/d and Pn-s/p/d coincide Fermi level at nonzero value, it reveals that the electrons of these orbitals contribute in the conduction process. The calculated values of the density of the states at Fermi level N(EF) and the associated electronic specific heat coefficient (γ) for the spin-up/down states are decreases with substituting P→As→Sb. The bonds nature and the interactions between the atoms for the spin-up/down configurations were investigated in (1 0 0) and (1 0 1) crystallographic planes.

Construction of flexible and wearable 3D TiO2 NTs@Ti mesh for physiological detection based on sweat

The biosensors with flexibility and breathability turn out to be a vital means of non-intrusive detection of multi-components biochemical markers in human sweat. For this end, three-dimensional (3D) structure TiO 2 nanotube arrays were in-situ established on Ti mesh by using the anodizing method in the present study. The 3D structure TiO 2 nanotube arrays@Ti mesh (3D TiO₂ NTs@Ti mesh) exhibited an anatase structure and a nanotube with pore size of 60–80 ​nm. 3D TiO₂ NTs@Ti mesh with good corrosion resistance made it possible to be a sweat sensor since the tube is capable of penetrating deeper into the pores to absorb more sweat, while mesh substrate exhibits high gas permeability to avoid skin damage. Sweat sensing performance was tested by using cyclic voltammetry (CV) curve, and the response current intensity increased with the increase in the concentrations of Na + , K + , urea and lactic acid while the current intensity decreases as the glucose concentration increases in the electrolyte solution. The semi-quantitative analysis was conducted to discriminate sweat component from each other, thereby revealing an effective recognition capability of the 3D TiO₂ NTs@Ti mesh. The density of the states (DOS) for anatase TiO₂ (101) nanotube that adsorbed different components were calculated. As suggested from the results, the adsorbed sweat components narrowed the band gap of anatase TiO 2 , thereby improving the current intensity.