Electronic structure and effective mass of pristine and Cl-doped CsPbBr_(3)

Organic–inorganic lead halide perovskites(LHPs) have attracted great interest owing to their outstanding optoelectronic properties.Typically,the underlying electronic structure would determinate the physical properties of materials.But as for now,limited studies have been done to reveal the underlying electronic structure of this material system,comparing to the huge amount of investigations on the material synthesis.The effective mass of the valance band is one of the most important physical parameters which plays a dominant role in charge transport and photovoltaic phenomena.In pristine CsPbBr_(3),the Fr?hlich polarons associated with the Pb–Br stretching modes are proposed to be responsible for the effective mass renormalization.In this regard,it would be very interesting to explore the electronic structure in doped LHPs.Here,we report high-resolution angle-resolved photoemission spectroscopy(ARPES) studies on both pristine and Cl-doped CsPbBr_(3).The experimental band dispersions are extracted from ARPES spectra along both ■ and ■ high symmetry directions.DFT calculations are performed and directly compared with the ARPES data.Our results have revealed the band structure of Cl-doped CsPbBr_(3) for the first time,which have also unveiled the effective mass renormalization in the Cl-doped CsPbBr_(3) compound.Doping dependent measurements indicate that the chlorine doping could moderately tune the renormalization strength.These results will help understand the physical properties of LHPs as a function of doping.

Probing nucleon effective mass splitting with light particle emission

The main objective of this study was to investigate the impact of effective mass splitting on heavy-ion-collision observables.We first analyzed correlations between different nuclear matter parameters obtained from 119 effective Skyrme interaction sets.The values of the correlation coefficients illustrate that the magnitude of effective mass splitting is crucial for tight constraints on the symmetry energy via heavy-ion collisions.The^(86)Kr+^(208)Pb system at beam energies ranging from 25 to 200A MeV was simulated within the framework of the improved quantum molecular dynamics model(ImQMD-Sky).Our calculations show that the slopes of the spectra of ln[Y(n)/Y(p)]and ln[Y(t)/Y(^(3)He)],which are the logarithms of the neutron to proton and triton to helium-3 yield ratios,are directly related to effective mass splitting and can be used to probe the effective mass splitting.

Discussion on the Electron and Hole Effective Masses in Thermal Silicon

This review and research study provides conclusive discussion on the electron and hole effective masses in thermal silicon dioxide placing their values at 0.42m and 0.58m,where m is the free electron mass,correct to two decimal places.Only one of the masses needs to be determined as the electron and hole masses in materials add up to be equal to free electron mass with the hole effective mass being larger than the electron effective mass.The review also convinces the reader that the CBO(conduction band offset)or the Si-SiO2 barrier height at the oxide/silicon interface of a Si MOS(metal-oxide-semiconductor)device is 3.20 eV.

Probing neutron–proton effective mass splitting using nuclear stopping and isospin mix in heavy-ion collisions in GeV energy region

The ramifications of the effective mass splitting on the nuclear stopping and isospin tracer during heavy-ion collisions within the gigaelectron volt energy region are studied using an isospin-dependent quantum molecular dynamics model.Three isotope probes,i.e.,a proton,deuteron,and triton,are used to calculate the nuclear stopping.Compared to the mn*>mp*case,the mn*<mp*parameter results in a stronger stopping for protons but a weaker stopping for tritons.The calculations of the isospin tracer show that the mn*>mp*parameter results in a higher isospin mix than the mn*<mp*parameter.The rapidity and impact parameter dependences of the isospin tracer are also studied.A constraining of the effective mass splitting using the free nucleons with high rapidity and in a central rather than peripheral collision is suggested.

Two-Layer High-Throughput:Effective Mass Calculations Including Warping

In this paper,we perform two-layer high-throughput calculations.In the first layer,which involves changing the crystal structure and/or chemical composition,we analyze selected Ⅲ-Ⅴ semiconductors,filled and unfilled skutterudites,as well as rock salt and layered chalcogenides.The second layer searches the full Brillouin zone(BZ)for critical points within 1.5 eV(1 eV=1.602176×10^(-19)J)of the Fermi level and characterizes those points by computing the effective masses.We introduce several methods to compute the effective masses from first principles and compare them to each other.Our approach also includes the calculation of the density-of-states effective masses for warped critical points,where traditional approaches fail to give consistent results due to an underlying non-analytic behavior of the critical point.We demonstrate the need to consider the band structure in its full complexity and the value of complementary approaches to compute the effective masses.We also provide computational evidence that warping occurs only in the presence of degeneracies.

Valence band structure and density of states effective mass model of biaxial tensile strained silicon based on k·p theory

After constructing a stress and strain model, the valence bands of in-plane biaxial tensile strained Si is calculated by k·p method. In the paper we calculate the accurate anisotropy valance bands and the splitting energy between light and heavy hole bands. The results show that the valance bands are highly distorted, and the anisotropy is more obvious. To obtain the density of states （DOS） effective mass, which is a very important parameter for device modeling, a DOS effective mass model of biaxial tensile strained Si is constructed based on the valance band calculation. This model can be directly used in the device model of metal-oxide semiconductor field effect transistor （MOSFET）. It also a provides valuable reference for biaxial tensile strained silicon MOSFET design.

The Harmonic Potential Theorem for a Quantum System with Time-Dependent Effective Mass

We investigate the many-body wave function of a quantum system with time-dependent effective mass, confined by a harmonic potential with time-dependent frequency, and perturbed by a time-dependent spatially homogeneous electric field. It is found that the wave function is comprised of a phase factor times the solution to the unperturbed time-dependent Schr6dinger equation with the latter being translated by a time-dependent value that satisfies the classical driven equation of motion. The wave function reduces to that of the harmonic potential theorem wave function when both the effective mass and frequency are static. An example of application is also given.

Effective Mass Model Reduced to Ordinary Mass Using Newton’s, Quantum and Generalized Special Relativity

The concept of the effective mass in crystals shows that the electron mass is affected by the crystal field and was experimentally verified. A useful expression for effective mass was obtained. Unfortunately this expression showed that the effective mass vanishes in the ab-sence of the external field. This is in conflict with observations which show that it reduces to the ordinary mass. To cure this defect a new model is developed assuming the existence of vacuum force as verified experimentally as shown by Casimir effect. Using Newton’s second law and the quantum expression of momentum, useful expressions were found. The same expression was found using generalized special relativity. Strikingly the three models reduced to the conventional one in the absence of vacuum, they also reduced to the ordinary electron mass in the absence of all forces.

How Initial Degrees of Freedom May Contribute to Initial Effective Mass, i.e. Effective Mass of the Universe Proportional to (D.O.F.) to the 1/4th Power by an Enormous Initial Degree of Freedom Value

Using a relationship between Hubble’s “parameter”, Temperature, Energy and effective mass, from there obtain in 3 + 1 dimensions a relationship between effective mass, and the initial degrees of freedom, to the 1/4th power, we will discuss candidates for entry into this, assuming for a start that initial universe conditions are similar to a black hole, i.e. a nearly singular start to inflationary expansion;this would necessitate a HUGE initial degree of freedom value as outlined in our argument.

Lowering plasma frequency by enhancing the effective mass of electrons: A route to deep sub-wavelength metamaterials

Deep sub-wavelength metamaterials are the key to the further development of practical metamaterials with small volumes and broadband properties. We propose to reduce the electrical sizes of metamaterials down to more sub-wavelength scales by lowering the plasma frequencies of metallic wires. The theoretical model is firstly established by analyzing the plasma frequency of continuous thin wires. By introducing more inductance elements, the effective electron mass can be enhanced drastically, leading to significantly lowered plasma frequencies. Based on this theory, we demonstrate that both the electric and the magnetic plasma frequencies of metamaterials can be lowered significantly and thus the electrical sizes of metamaterials can be reduced to more sub-wavelength scales. This provides an efficient route to deep sub-wavelength metamaterials and will give rigorous impetus for the further development of practical metamaterials.

Enhancing thermoelectric performance of n-type AgBi_(3)S_(5)through synergistically optimizing the effective mass and carrier mobility

AgBi_(3)S_(5) is a new n-type thermoelectric material that is environmentally friendly and composed of elements of earth-abundant,non-toxic and high performance-cost ratio.This compound features an intrinsically low thermal conductivity derived from its complex monoclinic structure.However,the terrible electrical transport properties greatly limited the improvement of thermoelectric performance.Most previous studies considered that carrier concentration is the main reason for low electrical conductivity and focused on improving carrier concentration by aliovalent ion doping.In this work,we found that the critical parameter that restricts the electric transport performance of AgBi_(3)S_(5)was the extremely low carrier mobility instead of the carrier concentration.According to the Pisarenko relationships and density functional theory calculations,Nb doping can sharpen the conduction band of AgBi_(3)S_(5),which contributes to reducing the effective mass and improving the carrier mobility.With a further increase of the Nb doping content,the conduction band convergence can enlarge the effective mass and preserve the carrier mobility.Combined with the decrease in lattice thermal conductivity due to the intensive phone scattering,a maximum ZT value of~0.50 at 773 K was achieved in Ag_(0.97)Nb_(0.03)Bi_(3)S_(5),which was~109.6%higher than that of pure AgBi3S5.This work will stimulate the new exploration of high-performance thermoelectric materials in ternary metal sulfides.

Bayesian inference on isospin splitting of nucleon effective mass from giant resonances in^(208)Pb

From a Bayesian analysis of the electric dipole polarizability,the constrained energy of isovector giant dipole resonance,the peak energy of isocalar giant quadrupole resonance,and the constrained energy of isocalar gi-ant monopole resonance in 208Pb,we extract the isoscalar and isovector effective masses in nuclear matter at satura-tion density ρ0 as m^(*)_(s.0)/m=0.87^(+)_(-004) and m^(*)_(v.0)/m=0.78^(+006)_(-006),respectively,at 90%confdence level.The con-straints obtained on m^(*)_(d.0) and m^(*)_(v.0) lead to a positive isospin splitting of nucleon effective mass in asymmetric nuclear matter of isospin asymmetry σ at ρ0 as m^(*)_(n-p)/m=(0.20^(0.15)_(0.14)σ.In addition,the symmetry energy at the subsatura-tion density ρ^(*)=0.05 fm^(-3) is determined to be E_(sym)(ρ^(*))=16.7±1.3 MeV at 90%confidence level.

Optimizing thermoelectric properties of BiSe through Cu additive enhanced effective mass and phonon scattering

Known as a weak topological insulator(TI),BiSe structurally exhibits alternating stacks of quantum spin Hall bilayer("Bi_(2)")and three-dimensional TI layer("Bi_(2)Se_(3)").The low lattice thermal conductivity of BiSe due to the presence of Bi2 bilayers promises potentially good thermoelectric performance.Herein,the thermoelectric properties of nominal Bi_(1-x)Cu_(x)Se samples were studied as the functions of the content of Cu additive and temperature.It is found that Cu additives in BiSe(1)profoundly affect the texture of densified polycrystalline samples by inclining the crystallographic c-axis parallel toward the pressure direction in the densification process,(2)increase considerably the effective mass and thus the Seebeck coefficient,and(3)yield point defects and Cu-Se secondary phases that effectively scatter heat-carrying phonons.As a result,the optimized electrical and thermal properties yield a thermoelectric figure of merit of zT~0.29 in Bi_(1-x)Cu_(x)Se(x=0.03)sample at 467 K in parallel to the pressure direction and a zT~0.20 at 468 K in the perpendicular direction.

Estimation of the potential performance in p-type SnSe crystals through evaluating weighted mobility and effective mass

It has been proved that the thermoelectric performance of p-type SnSe crystals can be optimized through enhancing carrier concentration.The calculations of electronic band structure elucidate that this approach can be interpreted by including multiple valence bands.To better estimate the potential performance,we proposed the transport properties for p-type SnSe crystals and analyzed the weighted mobility from the experimental results.The weighted mobility approaches~600 cm^(2)V1s1 when the carrier concentration is as high as~6.31019 cm3.Combined with obtained lattice thermal conductivity,through rising carrier concentration,the quality factor B possesses significant improvements of~235%and 138%at 300 K and 773 K,respectively.Through comparing weighted mobility and Hall mobility,two effective mass values~0.9 me and 1.8 me can be derived using carrier concentrations.It is expected that the ZT~1.0 at 300K and ZT~2.9 at 773 K can be obtained when the carrier concentration of~8.01019 cm3 and the effective mass~1.8 me were selected.This work provides an alternative way to comprehend the performance optimization in thermoelectric community.

First-principle high-throughput calculations of carrier effective masses of two-dimensional transition metal dichalcogenides

Two-dimensional group-VIB transition metal dichalcogenides（with the formula of MX2） emerge as a family of intensely investigated semiconductors that are promising for both electronic（because of their reasonable carrier mobility） and optoelectronic（because of their direct band gap at monolayer thickness） applications. Effective mass is a crucial physical quantity determining carriers transport, and thus the performance of these applications. Here we present based on first-principles high-throughput calculations a computational study of carrier effective masses of the two-dimensional MX2 materials. Both electron and hole effective masses of different MX2（M = Mo, W and X = S, Se, Te）, including in-layer/out-of-layer components, thickness dependence, and magnitude variation in heterostructures, are systemically calculated. The numerical results, chemical trends, and the insights gained provide useful guidance for understanding the key factors controlling carrier effective masses in the MX2 system and further engineering the mass values to improve device performance.

Enhanced thermoelectric performance in Cl-doped BiSbSe_(3) with optimal carrier concentration and effective mass

Possessing inherently low thermal conductivity,BiSbSe_(3) is a promising thermoelectric material for medium temperature.Therefore,to substantially optimize the thermoelectric performance of BiSbSe_(3),researchers mainly focus on the strategies to improve its electrical transport properties.Among these strongly coupled thermoelectric parameters,carrier concentration and effective mass are two intrinsic variables to decisively affect the electrical transport properties.In this work,Cl as a donor dopant is effective to provide extra electrons in n-type BiSbSe_(3),and the carrier concentration and effective mass can be well optimized simultaneously with increasing Cl content owing to the multiple conduction bands in BiSbSe_(3).What’s more,maximum weighted mobility~53 cm^(2)V^(-1)s^(-1)is obtained in Cl-doped BiSbSe_(3),which contributes to a largely enhanced power factor~4.8μW cm^(-1)K^(-2)at room temperature and outperforms other halogen-doped BiSbSe_(3) samples.Finally,combining the significantly enhanced power factor and maintained low thermal conductivity,a maximum ZT~1.0 is achieved in Cl-doped BiSbSe_(3) at 800 K.

First-principles investigation of electronic structure,effective carrier masses, and optical properties of ferromagnetic semiconductor CdCr_2S_4

The electronic structures, the effective masses, and optical properties of spinel CdCr_2S_4 are studied by using the fullpotential linearized augmented planewave method and a modified Becke–Johnson exchange functional within the densityfunctional theory. Most importantly, the effects of the spin–orbit coupling（SOC） on the electronic structures and carrier effective masses are investigated. The calculated band structure shows a direct band gap. The electronic effective mass and the hole effective mass are analytically determined by reproducing the calculated band structures near the BZ center.SOC substantially changes the valence band top and the hole effective masses. In addition, we calculated the corresponding optical properties of the spinel structure CdCr_2S_4. These should be useful to deeply understand spinel CdCr_2S_4 as a ferromagnetic semiconductor for possible semiconductor spintronic applications.

Isospin splitting of nucleon effective mass and symmetry energy in isotopic nuclear reactions

Within an isospin and momentum dependent transport model, the dynamics of isospin particles（nucleons and light clusters） in Fermi-energy heavy-ion collisions are investigated for constraining the isospin splitting of nucleon effective mass and the symmetry energy at subsaturation densities. The impacts of the isoscalar and isovector parts of the momentum dependent interaction on the emissions of isospin particles are explored, i.e., the mass splittings of m_n^＊=m_p^＊ and m_n^＊〉 m_p^＊（m_n^＊〈 m_p^＊）. The single and double neutron to proton ratios of free nucleons and light particles are thoroughly investigated in the isotopic nuclear reactions of ^112Sn＋^112Sn and ^124Sn＋^124Sn at incident energies of 50 and 120 MeV/nucleon, respectively. It is found that both the effective mass splitting and symmetry energy impact the kinetic energy spectra of the single ratios, in particular at the high energy tail（larger than 20 Me V）. The isospin splitting of nucleon effective mass slightly impacts the double ratio spectra at the energy of 50 MeV/nucleon. A soft symmetry energy with stiffness coefficient of γ_s =0.5 is constrained from the experimental data with the Fermi-energy heavy-ion collisions.

Tunable band structure and effective mass of disordered chalcopyrite

The band structure and effective mass of disordered chalcopyrite photovoltaic materials Cul-xAgxGaX2 （X = S, Se） are investigated by density functional theory. Special quasirandom structures are used to mimic local atomic disorders at Cu/Ag sites. A local density plus correction method is adopted to obtain correct semiconductor band gaps for all compounds. The bandgap anomaly can be seen for both sulfides and selenides, where the gap values of Ag compounds are larger than those of Cu compounds. Band gaps can be modulated from 1.63 to 1.78 eV for CU1-xAgxGaSe2, and from 2.33 to 2.64 eV for Cu1-xAgxGaS2. The band gap minima and maxima occur at around x = 0.5 and x = 1, respectively, for both sulfides and selenides. In order to show the transport properties of Cu1-xAgxGaX2, the effective mass is shown as a function of disordered Ag concentration. Finally, detailed band structures are shown to clarify the phonon momentum needed by the fundamental indirect-gap transitions. These results should be helpful in designing high-efficiency photovoltaic devices, with both better absorption and high mobility, by Ag-doping in CuGaX2.

Generalized stiffness and effective mass coefficients for power-law Euler-Bernoulli beams

We extend the well-known concept and results for lumped parameters used in the spring-like models for linear materials to Hollomon’s power-law materials.We provide the generalized stiffness and effective mass coefficients for the power-law Euler-Bernoulli beams under standard geometric and load conditions.In particular,our mass-spring lumped parameter models reduce to the classical models when Hollomon’s law reduces to Hooke’s law.Since there are no known solutions to the dynamic power-law beam equations,solutions to our mass lumped models are compared to the low-order Galerkin approximations in the case of cantilever beams with circular and rectangular cross-sections.