Function Of Chemical Potential Research Articles

Entropy per particle spikes in the transition metal dichalcogenides

We derive a general expression for the entropy per particle as a function of chemical potential, temperature and gap magnitude for the single layer transition metal dichalcogenides. The electronic excitations in these materials can be approximately regarded as two species of the massive or gapped Dirac fermions. Inside the smaller gap there is a region with zero density of states where the dependence of the entropy per particle on the chemical potential exhibits a huge dip-and-peak structure. The edge of the larger gap is accompanied by the discontinuity of the density of states that results in the peak in the dependence of the entropy per particle on the chemical potential. The specificity of the transition metal dichalcogenides makes possible the observation of these features at rather high temperatures order of 100 K. The influence of the uniaxial strain on the entropy per particle is discussed.

A survey of acceptor dopants for β-Ga2O3

With a wide band gap, high critical breakdown voltage and commercially available substrates, Ga2O3 is a promising material for next-generation power electronics. Like most wide-band-gap semiconductors, obtaining better control over its electrical conductivity is critically important, but has proven difficult to achieve. Although efficient p-type doping in Ga2O3 is not expected, since theory and experiment indicate the self-trapping of holes, the full development of this material will require a better understanding of acceptor dopants. Here the properties of group 2, group 5 and group 12 acceptor impurities in β-Ga2O3 are explored using hybrid density functional calculations. All impurities are found to exhibit acceptor transition levels above 1.3 eV. After examining formation energies as a function of chemical potential, Mg (followed closely by Be) is determined to be the most stable acceptor species.

Tunable Bragg defect mode in one-dimensional photonic crystal containing a graphene-embedded defect layer.

Using the transfer matrix method, the transmission properties of defective one-dimensional photonic crystal are analyzed in the terahertz region. The defect layer is composed of a graphene-embedded dielectric layer. We investigate the variation of the defect mode's frequency as a function of graphene chemical potential for different values of incident angles. The numerical results show that the frequency of the defect mode can be tuned effectively as the chemical potential of graphene nanolayers changes using an applied gate voltage. The present results can be useful in designing tunable graphene-based photonic devices such as filters and sensors in terahertz regions.

On the Prediction of Water Contents in Na-Saturated Dioctahedral Smectites

Properties of swellable clay minerals in technical and geotechnical applications as well as in geological systems are determined by their water content. Thereby, the water content depends on the structure and morphology of the smectites and available water while smectites are the most heterogeneous clay minerals. Here, first-principles calculations are combined with ab initio thermodynamics to systematically study the hydration states of Na-saturated dioctahedral smectites. Total energy calculations based on density functional theory are carried out for a series of montmorillonites and beidellites with varying layer charge (0.125 ≤ ξ ≤ 0.5) and increasing number of water molecules per unit cell. The thermodynamic ground state was then defined with the help of the grand canonical potential as a function of chemical potential of water, which is directly related to the experimental conditions of pressure and temperature. For the first time, p,T-phase diagrams of stable hydration states together with relative...

Theoretical investigations on diamondoids (CnHm, n = 10-41): Nomenclature, structural stabilities, and gap distributions.

Combining the congruence check and the first-principles calculations, we have systematically investigated the structural stabilities and gap distributions of possible diamondoids (CnHm) with the carbon numbers (n) from 10 to 41. A simple method for the nomenclature is proposed, which can be used to distinguish and screen the candidates with high efficiency. Different from previous theoretical studies, the possible diamondoids can be enumerated according to our nomenclature, without any pre-determination from experiments. The structural stabilities and electronic properties have been studied by density functional based tight binding and first-principles methods, where a nearly linear correlation is found between the energy gaps obtained by these two methods. According to the formation energy of structures, we have determined the stable configurations as a function of chemical potential. The maximum and minimum energy gaps are found to be dominated by the shape of diamondoids for clusters with a given number of carbon atoms, while the gap decreases in general as the size increases due to the quantum confinement.

Confinement-deconfinement transition in dense SU(2) QCD

In this report we study the properties of the dense SU(2) QCD. The lattice simulations are carried out with improved gauge action and smaller lattice spacing as compared to our previous work. This allowed us to approach closer to the continuum limit and reach larger densities without lattice artifacts. We measured string tension and Polyakov loop as functions of chemical potential and temperature. At suffciently large baryon density and zero temperature we observe confinement/deconfinement transition which manifests itself as a vanishing of the string tension and rising of the Polyakov loop.

Status of Complex Langevin

I review the status of the Complex Langevin method, which was invented to make simulations of models with complex action feasible. I discuss the mathematical justification of the procedure, as well as its limitations and open questions. Various pragmatic measures for dealing with the existing problems are described. Finally I report on the progress in the application of the method to QCD, with the goal of determining the phase diagram of QCD as a function of temperature and baryonic chemical potential.

Sulfide oxide XZnSO (X = Ca or Sr) as novel active photocatalytic water splitting solar-to-hydrogen energy conversion

The photocatalytic, structural and transport properties of the newly synthesized sulfide oxide CaZnSO and SrZnSO compounds are comprehensively investigated by means of first and second-principles calculation in order to explain the semiconductor's ‘photo-excitation' state mechanism in CaZnSO and SrZnSO. At the same time, the influence of the substitution of Ca2+ by Sr2+ on the structural properties and, hence, on the photocatalytic properties, are investigated. The optical conductivity and the absorption level exhibit an obvious enhancement from the ultraviolet to the visible light region when we move from Ca to Sr. This shows that the absorption edge moves from λ=387.4→λ=442.7nm, which corresponds to the direct optical band gap of 3.2eV→2.8eV, which is well matched with the solar spectrum and the sufficient negative conduction band potential for reduction of H+/H2. The calculated electronic band structure and the angular momentum character of various structures confirm that CaZnSO and SrZnSO possess a direct fundamental energy band gap of about 3.7eV (CaZnSO)→3.1eV (SrZnSO), and the electronic charge distribution reveals a clear map of the electronic charge transfer and the chemical bonding. Furthermore, the carrier concentration (n) as a function of chemical potential at three constant temperatures (T) and n as a function of T at fixed chemical potential were calculated. It was found that n increases exponentially with increasing T and reveals that the CaZnSO and SrZnSO are p-type semiconductors. Based on these results, one can conclude that CaZnSO and SrZnSO satisfied all requirements to be an efficient photocatalyst. This will greatly improve the search efficiency and greatly help experiments to save resources in the exploration of new photocatalysts with good photocatalytic performance.

Insight of DFT and ab initio atomistic thermodynamics on the surface stability and morphology of In2O3

In2O3 catalysts show remarkable activity and selectivity in methanol synthesis from CO2 hydrogenation. In order to get insight into the surface stability of this catalyst, density functional theory and ab initio atomistic thermodynamics method were used to investigate the surface free energies of various facets as a function of oxygen chemical potential, as well as the influences of temperature, pressure and gas compositions. The results show that the (111) facet presents lowest surface free energy under oxygen-rich condition, while the indium-terminated (100) facet is the most stable one under oxygen-lean condition. Moreover, we applied Wulff construction to determine the equilibrium shape of In2O3 with different oxygen chemical potentials. The equilibrium shape under oxygen-lean condition is cubic, which only expose (100) facet, while, the equilibrium shape under oxygen-rich condition is octahedron, which only expose (111) facet. Meanwhile, the results agree well with what is observed experimentally. It is further predicted that Wulff shape of In2O3 exists in a truncated octahedron morphology in which the (100) surface becomes predominant plane under CO2 hydrogenation reaction conditions.

Electronic and Thermoelectric Properties of Ternary Chalcohalide Semiconductors: First Principles Study

Ternary chalcohalides have been widely utilized for different device applications. The thermoelectric properties of SbSI, SbSeI and SbSBr have been investigated by theoretical simulations, and the findings have been performed using BoltzTraP code, based on semi-classical Boltzmann transport theory. In this study, we simulated the electronic structures using the Englo-Vosko generalized gradient approximation employed in the WIEN2k program. From the electronic band structures, we found a combination of light and heavy bands around the Fermi level in the valence band, which strongly affect the effective masses of the carriers. The entire thermoelectric parameters, like the electrical, the electronic part of the thermal conductivities, the Seebeck coefficient and the power factor have been analysed as functions of temperature and chemical potential. The correlation between the effective masses and the thermoelectric properties is also included in the discussion because the effective mass reveals the mobility of the carriers which in turn affect the thermoelectric properties. The substitution of sulfur reveals high electrical conductivity and a smaller Seebeck coefficient based on effective mass leads to the increase in the power factor.

Majorana states in prismatic core-shell nanowires

We consider core-shell nanowires with conductive shell and insulating core and with polygonal cross section. We investigate the implications of this geometry on Majorana states expected in the presence of proximity-induced superconductivity and an external magnetic field. A typical prismatic nanowire has a hexagonal profile, but square and triangular shapes can also be obtained. The low-energy states are localized at the corners of the cross section, i.e., along the prism edges, and are separated by a gap from higher energy states localized on the sides. The corner localization depends on the details of the shell geometry, i.e., thickness, diameter, and sharpness of the corners. We study systematically the low-energy spectrum of prismatic shells using numerical methods and derive the topological phase diagram as a function of magnetic field and chemical potential for triangular, square, and hexagonal geometries. A strong corner localization enhances the stability of Majorana modes to various perturbations, including the orbital effect of the magnetic field, whereas a weaker localization favorizes orbital effects and reduces the critical magnetic field. The prismatic geometry allows the Majorana zero-energy modes to be accompanied by low-energy states, which we call pseudo Majorana, and which converge to real Majoranas in the limit of small shell thickness. We include the Rashba spin-orbit coupling in a phenomenological manner, assuming a radial electric field across the shell.

Entropy spikes as a signature of Lifshitz transitions in the Dirac materials

We demonstrate theoretically that the characteristic feature of a 2D system undergoing N consequent Lifshitz topological transitions is the occurrence of spikes of entropy per particle s of a magnitude ±ln2/(J − 1/2) with 2 ≤ J ≤ N at low temperatures. We derive a general expression for s as a function of chemical potential, temperature and gap magnitude for the gapped Dirac materials. Inside the smallest gap, the dependence of s on the chemical potential exhibits a dip-and-peak structure in the temperature vicinity of the Dirac point. The spikes of the entropy per particles can be considered as a signature of the Dirac materials. These distinctive characteristics of gapped Dirac materials can be detected in transport experiments where the temperature is modulated in gated structures.

Phenomenology of the soft gap, zero-bias peak, and zero-mode splitting in ideal Majorana nanowires

We theoretically consider the observed soft gap in the proximity-induced superconducting state of semiconductor nanowires in the presence of spin-orbit coupling, Zeeman splitting, and tunneling leads, but in the absence of any extrinsic disorder. We critically consider the effects of three distinct intrinsic physical mechanisms (tunnel barrier to normal leads, temperature, and dissipation) on the phenomenology of the gap softness in the tunnel spectroscopy of the normal-superconductor junction as a function of spin splitting and chemical potential. We find that all three mechanisms individually can produce a soft gap, leading to calculated conductance spectra qualitatively mimicking experimental results. We also show that the phenomenology of the soft gap is intrinsically tied to the broadening and the height of the Majorana zero mode(MZM)-induced differential conductance peak above the topological quantum phase transition point with both the soft gap and the quality of the MZM being simultaneously affected by tunnel barrier, temperature, and dissipation. We establish that the MZM splitting oscillations can be suppressed by temperature or dissipation, but not by the tunnel barrier. Since all three mechanisms are likely to be present in any realistic nanowires, discerning the effects of various mechanisms is difficult, necessitating detailed experimental data as a function of all the system parameters, some of which (e.g., dissipation, chemical potential, tunnel barrier) may not be known experimentally. While the tunneling-induced soft-gap behavior is benign with no direct adverse effect on the Majorana topological properties with the zero-bias peak remaining quantized at $2e^2/h$, the soft gap induced by finite temperature and/or finite dissipation is detrimental to topological properties and must be avoided as much as possible.

Andreev bound states versus Majorana bound states in quantum dot-nanowire-superconductor hybrid structures: Trivial versus topological zero-bias conductance peaks

Motivated by an important recent experiment [Deng et al., Science 354, 1557 (2016)], we theoretically consider the interplay between Andreev bound states(ABSs) and Majorana bound states(MBSs) in quantum dot-nanowire semiconductor systems with proximity-induced superconductivity(SC), spin-orbit coupling and Zeeman splitting. The dot induces ABSs in the SC nanowire which show complex behavior as a function of Zeeman splitting and chemical potential, and the specific question is whether two such ABSs can come together forming a topological MBS. We consider physical situations involving the dot being non-SC, SC, or partially SC. We find that the ABSs indeed tend to coalesce together producing near-zero-energy midgap states as Zeeman splitting and/or chemical potential are increased, but this mostly happens in the non-topological regime although there are situations where the ABSs could come together forming a topological MBS. The two scenarios(two ABSs forming a near-zero-energy non-topological ABS or a zero-energy topological MBS) are difficult to distinguish by tunneling conductance spectroscopy due to essentially the same signatures. Theoretically we distinguish them by knowing the critical Zeeman splitting for the topological quantum phase transition or by calculating the topological visibility. We find that the "sticking together" propensity of ABSs to produce a zero-energy midgap state is generic in class D systems, and by itself says nothing about the topological nature of the underlying SC nanowire. One must use caution in interpreting tunneling conductance measurements where the midgap sticking-together behavior of ABSs cannot be construed as definitive evidence for topological SC with non-Abelian MBSs. We also suggest some experimental techniques for distinguishing between trivial and topological ZBCPs.

Initial-Stage Oxidation of Ni3Al(100) and -(110) from Ab Initio Thermodynamics

The microscopic mechanisms of the initial-stage oxidation of the Ni3Al(100) and Ni3Al(110) surfaces are comparatively studied using ab initio calculations based on density-functional theory and thermodynamics considerations. The surface energies of the two surfaces as functions of aluminum and oxygen chemical potentials are constructed and show that the formation of any antisite defects is not favorable at the Ni3Al(100) surface, whereas Al antisite defects are favorable at the Ni3Al(110) surface. The surface phase diagrams of the Ni3Al(100) and -(110) surfaces with different antisite defects and at the various oxygen coverages are determined. These results show that oxygen adsorption enhances Al surface segregation at the initial stage of oxidation for both surfaces and that the Ni3Al(100) surface is thermodynamically more favored to oxidize completely at a lower oxygen coverage than the Ni3Al(110) surface.

Higher-order baryon number susceptibilities: Interplay between the chiral and the nuclear liquid-gas transitions

We use an improved version of the SU(3) flavour parity-doublet quark-hadron model to investigate the higher order baryon number susceptibilities near the chiral and the nuclear liquid-gas transitions. The parity-doublet model has been improved by adding higher-order interaction terms of the scalar fields in the effective mean field Lagrangian, resulting in a much-improved description of nuclear ground-state properties, in particular the nuclear compressibility. The resulting phase diagram of the model agrees qualitatively with expectations from lattice QCD, i.e., it shows a crossover at zero net baryo-chemical potential and a critical point at finite density. Using this model, we investigate the dependence of the higher-order baryon number susceptibilities as function of temperature and chemical potential. We observe a strong interplay between the chiral and liquid-gas transition at intermediate baryo chemical potentials. Due to this interplay between the chiral and the nuclear liquid-gas transitions, the experimentally measured cumulants of the net baryon number may show very different beam energy dependence, subject to the actual freeze-out temperature.

Thermoelectric properties of [formula omitted] for device applications: A first principle TB-mBJ potential study

Here we report the structural, electronic, optical, and thermoelectric properties of delafossite type 2H-CuGaO2 using first principles calculations. The present calculation predict an indirect band gap of 1.20eV and a direct band gap of 3.48eV. A detailed analysis of the electronic structure is provided based on atom and orbital projected density of states. Frequency dependent dielectric functions, refractive index, and absorption coefficient as a function of photon energy are discussed. The thermoelectric properties with power factor, and the figure of merit are reported as a function of chemical potential in the region ±0.195(μ−EF)eV at constant temperature of 300 and 800K. The thermoelectric properties shows that 2H-CuGaO2 could be potential candidate for engineering devises operating at high temperature for the chemical potential in the range of ±0.055(μ−EF)eV and beyond this range the thermoelectric performance of 2H-CuGaO2 get reduced.

Electron doping effects on the electrical conductivity of zigzag carbon nanotubes and corresponding unzipped armchair graphene nanoribbons

The Kubo formula is used to extract the electrical conductivity (EC) of different diameters of doped zigzag carbon nanotubes and their corresponding unzipped armchair graphene nanoribbons, as a function of temperature and chemical potential, within the tight-binding Hamiltonian model and Green's functions approach. The results reveal more sensitivity to temperature for semiconducting systems in addition to a decrease in EC of all systems with increasing cross-sections.

Propagation of electromagnetic waves in extremely dense media

We study the propagation of electromagnetic (EM) waves in extremely dense exotic systems with very unique properties. These EM waves develop a longitudinal component due to interactions with the medium. Renormalization scheme of QED is used to understand the propagation of EM waves in both longitudinal and transverse directions. The propagation of EM waves in a quantum statistically treatable medium affects the properties of the medium itself. The electric permittivity and the magnetic permeability of the medium are modified and influence the related behavior of the medium. All the electromagnetic properties of a medium become a function of temperature and chemical potential of the medium. We study in detail the modifications of electric permittivity and magnetic permeability and other related properties of a medium in the superdense stellar objects.

Exploration of thermoelectricity in ScRhTe and ZrPtPb Half Heusler compounds: A first principle study

Motivated by the results of other well known Half Heusler compounds, the structural, electronic, phonon and thermoelectric properties of two novel Half Heusler compounds ScRhTe and ZrPtPb are thoroughly investigated with the frame work of first principle calculations and semi classical Boltzmann equations with constant relaxation time approximation. These materials show direct band semiconductors nature with band gap 0.43 eV (ScRhTe) and 0.83 eV (ZrPtPb) respectively. The phonon dispersion curves indicate that these compounds are thermodynamically stable. The Seebeck coefficient, electrical conductivity, electronic thermal conductivity and power factor as function of chemical potential are evaluated in this report. These materials have high power factor for n-type doping. The lattice thermal conductivity of these materials decreases with increase in temperature. The calculated results divulge that these materials are potential candidates for thermoelectric applications.