Showing papers on "Debye published in 2021"

Cold quark matter at (NLO)-L-3 : Soft contributions

Abstract: In a tour de force calculation, using new computational techniques, the authors compute the contribution of soft gluons, gluons with momenta smaller than the Debye screening mass, to the pressure of cold nuclear matter, a QCD medium at zero temperature but large chemical potential, at next-to-next-to-next-to-leading order.

Explorations of elastic anisotropies and thermal properties of the hexagonal TMSi2 (TM = Cr, Mo, W) silicides from first-principles calculations

Abstract: In this study, the first-principles (DFT) is used to explore the structural properties, elastic anisotropies, and thermal properties of hexagonal TMSi2 (TM = Cr, Mo, W) silicides. The elastic properties of single-crystal and poly-crystal are acquired by using Voigt-Reuss-Hill approximations method. The hardness of TMSi2 silicides were calculated from the bulk B and shear moduli G; In addition, the results show that hexagonal TMSi2 silicide is not potentially super-hard materials. Meanwhile, in terms of their Poisson’s ratio, GH/BH and Cauchy pressures, TMSi2 silicides are brittle material. Elastic anisotropies of TMSi2 silicides are measured by using anisotropy index of elastic properties, 3D surface constructions of elastic moduli and their two-dimensional planar projections were used to indicate the elastic anisotropies of these TMSi2 silicides. The sequence of elastic anisotropy follows as WSi2 > MoSi2 > CrSi2. Finally, the sound velocities, Debye temperatures, thermal conductivity and their anisotropies of these silicides were discussed, the sound velocities and Debye temperature of these TMSi2 silicides are anisotropic in the [100] and [001] directions.

Long-Range Fluctuation-Induced Forces in Driven Electrolytes.

Abstract: We study the stochastic dynamics of an electrolyte driven by a uniform external electric field and show that it exhibits generic scale invariance despite the presence of Debye screening. The resulting long-range correlations give rise to a Casimir-like fluctuation-induced force between neutral boundaries that confine the ions; this force is controlled by the external electric field, and it can be both attractive and repulsive with similar boundary conditions, unlike other long-range fluctuation-induced forces. This work highlights the importance of nonequilibrium correlations in electrolytes and shows how they can be used to tune interactions between uncharged biological or synthetic structures at large separations.

First-principles exploration of elastic anisotropy and thermal properties of the C40-type VSi2, NbSi2, and TaSi2 disilicides

Abstract: The anisotropy in elastic and thermal properties of the C40-type TMSi2 (TM = Ta, Nb, V) disilicides were calculated by DFT. The Voigt–Reuss–Hill approximation method was applied to analyze the elastic constants. The anisotropy in elastic of these TMSi2 disilicides were characterized by 3D surface constructions and 2D planar projections. The arrangement of anisotropy in elastic modulus is TaSi2 > NbSi2 > VSi2. Based on the directional sound velocities and Debye temperatures, they are also anisotropic. The minimum thermal conductivities of TMSi2 (TM = Ta, Nb, V) disilicides were calculated by Cahill’s model and Clarke’s model, and the anisotropy is sequenced as TaSi2 > NbSi2 > VSi2.

Multiple ferroelectric nematic phases of a highly polar liquid crystal compound

Abstract: Ferroelectric nematic liquid crystals represent not only interesting fundamental science, but they also hold promise for storage capacitors with high power density or new information display technology having sub-millisecond switching. In this work we describe the synthesis and measurements of the physical properties of a new highly polar ferroelectric nematic compound, 4-nitrophenyl 4-[(2,4-dimethoxylbenzoyl)oxy]-2-fluorobenzoate (RT11001). The dipole moment of this material (along the long molecular axis) is calculated to exceed 11.5 Debye. We employ a wide range of physical characterization methods including differential scanning calorimetry (DSC), mass density measurement, optical birefringence, polarizing optical microscopy (POM), electric current analysis, and electro-optical switching, to show that RT11001 has three distinct ferroelectric states, F1, F2 and F3. F1 is purely orientationally ordered ferroelectric nematic phase (NF), F2 has a ferroelectric nematic with possibly short-range hexagonal order normal to the director (NhF), and we conjecture that F3 has a long-range hexagonal order normal to the director (ColhF).

Permittivity Characterization of Dispersive Materials Using Power Measurements

Abstract: This article presents an inexpensive transmission line (TL) approach to reconstruct the dielectric properties of dispersive and non-dispersive materials, with low or high loss. This method uses amplitude-only transmission measurements, namely power measurements, thereby removing the need for phase measurements. The proposed method only requires a signal generator and a power sensor for complex permittivity characterization without the need for either a scalar or a vector network analyzer. In the proposed method, a Debye model for the frequency dispersion of the material under test (MUT) is used; however, the applicability extends to other models. A coaxial line is considered as an ideal TL, and by using the inverse solution of the forward scattering equation in different frequencies, which requires numerically solving a system of nonlinear equations, the Debye parameters are extracted. For experimental validation, a suspended coaxial line was designed and fabricated. The permittivities of several liquid chemicals were measured within a frequency band of 0.3–3 GHz to demonstrate the validity of the technique.

Nonuniform Debye Temperatures in Quasi-One-Dimensional Transition-Metal Trichalcogenides

Abstract: The Debye–Waller factor plots for S 2p core-level, based on temperature-dependent X-ray photoemission measurements on quasi-one-dimensional (1D) chains of TiS3, suggest effective Debye temperatures...

Analytical solutions for the hydrogen atom in plasmas with electric, magnetic, and Aharonov-Bohm flux fields.

Abstract: The combined effects of external electric, magnetic, and Aharonov-Bohm (AB) flux fields on the two-dimensional hydrogen atom embedded in both Debye and quantum plasmas modeled by the more general exponential cosine Coulomb (MGECSC) potential are investigated using the general analytic approach, namely the homotopy analysis method (HAM). The analytical convergent solutions are obtained for the ground state as well as excited states at both weak and strong intensity of the external fields. The influence of the screening parameters on the quantum levels are exhaustively explored in the presence of three external fields. It is worth emphasizing that our analytical HAM results have 4-10 digits of accuracy in comparison with the numerical results. In the framework of the HAM method, there is no any small parameter different from the perturbation. Owing to this advantage, the convergent accurate solutions always can be obtained by the HAM approach even for the strong external fields. There is no limit to the value of the parameters or the strength of the external fields. It is also observed that the combined effects of the external fields play an important role on the interaction potential profile and the applied external magnetic field is the most dominant in the hydrogen atomic system. Also note that the combined effect of the fields is stronger than individual effects in both Debye and quantum plasmas. The findings obtained by the HAM-based approach in this study shed substantial light on the more complicated problems in plasmas for the atomic systems or molecular physics.

Explaining the specific heat of liquids based on instantaneous normal modes.

Abstract: The successful prediction of the specific heat of solids is a milestone in the kinetic theory of matter due to Debye. No such success, however, has ever been obtained for the specific heat of liquids, which has remained a mystery for over a century. A theory of specific heat of liquids is derived here using a recently proposed analytical form of the vibrational density of states of liquids, which takes into account saddle points in the liquid energy landscape via the so-called instantaneous normal modes (INMs), corresponding to negative eigenvalues (imaginary frequencies) of the Hessian matrix. The theory is able to explain the typical monotonic decrease in specific heat with temperature observed in liquids in terms of the average INM excitation lifetime decreasing with $T$ (in accordance with the Arrehnius law) and provides an excellent single-parameter fitting to several sets of experimental data for atomic and molecular liquids. It also correlates the height of the liquid energy barrier with the slope of the specific heat in the function of temperature in accordance with the available data. These findings demonstrate that the specific heat of liquids is controlled by the instantaneous normal modes, i.e., by localized unstable (exponentially decaying) vibrational excitations and provide the missing connection among anharmonicity, saddle points in the energy landscape, and the thermodynamics of liquids.

Electronic and magnetic investigation of half-metallic ferrimagnetic full-Heusler Mn2IrGe

Abstract: In this study, we are interested in the calculations of physicochemical properties of a new full-Heusler Mn2IrGe alloy. The calculations are performed by the full-potential linearized augmented plane wave (FP-LAPW) method within the spin density-functional theory. As exchange–correlation potential, the generalized gradient approximation formulated by Perdew, Burke, and Ernzerhof (GGA-PBE) and the modified Becke-Johnson potential (mBJ)-GGA-PBE were used. Our results have shown the structural stability and ductile character for Mn2IrGe in the CuHg2Ti-type structure. The magnetic and electronic properties reveal a half-metallic ferrimagnetic (HM-FIM) behavior of Mn2IrGe at the equilibrium lattice parameter which can be influenced by the variation of hydrostatic pressure. An integer value equal to 3 μB has been recorded for the total magnetic moment, and it is in good agreement with the Slater–Pauling rule. The thermodynamic properties including Debye temperature, heat capacity, and entropy have been estimated with different temperatures and pressures using the Debye quasi-harmonic model. This new full-Heusler can be viewed as a good candidate for spintronics.

Resummed gluon propagator and Debye screening effect in a holonomous plasma

Abstract: Based on the Dyson-Schwinger equation, we compute the resummed gluon propagator in a holonomous plasma that is described by introducing a constant background field for the vector potential ${A}_{0}$. Because of the transversality of the holonomous hard thermal loop in gluon self-energy, the resummed propagator has a similar Lorentz structure as that in the perturbative quark-gluon plasma where the holonomy vanishes. As for the color structures, since diagonal gluons are mixed in the overcomplete double-line basis, only the propagators for off-diagonal gluons can be obtained unambiguously. On the other hand, multiplied by a projection operator, the propagators for diagonal gluons, which exhibit a highly nontrivial dependence on the background field, are uniquely determined after summing over the color indices. As an application of these results, we consider the Debye screening effect on the in-medium binding of quarkonium states by analyzing the static limit of the resummed gluon propagator. In general, introducing nonzero holonomy merely amounts to modifications on the perturbative screening mass ${m}_{D}$ and the resulting heavy-quark potential, which remains the standard Debye screened form, is always deeper than the screened potential in the perturbative quark-gluon plasma. Therefore, a weaker screening and, thus, a more tightly bounded quarkonium state can be expected in a holonomous plasma. In addition, both the diagonal and off-diagonal gluons become distinguishable by their modified screening masses ${\mathcal{M}}_{D}$, and the temperature dependence of the ratio ${\mathcal{M}}_{D}/T$ shows a very similar behavior as that found in lattice simulations.

Non-Debye segmental relaxation of poly-N-vinyl-carbazole in dilute solution

Abstract: Ultrasonic absorption measurements were carried out for poly-N-vinyl-carbazole in dilute 1,2-dichloro-ethane solution at frequencies from 1 to 50 MHz over a temperature range of 10–45°C with increm...

Structural stabilities and thermal properties of η′-Mg2Zn5-Al2+ and η-MgZn2 phase in Al–Zn–Mg alloy: first-principles calculation and quasi-harmonic Debye approximation

Abstract: The structural stabilities and thermal properties of η′ and η phase at high temperature and pressure were investigated via first principles calculations combined with quasi-harmonic Debye approximation (QHA). The calculated results illustrate η′ possess high formation enthalpy with lower structural stability at high temperature, which may transits to equilibrium phase η at temperature range of 510–520 K. The calculated thermodynamic properties indicate η exhibits better thermal stability than η′ at high temperature. The thermoelastic properties of η′ and η were estimated based on the temperature-dependent elastic constants Cij(T), and it is revealed the elastic moduli of η′ are larger than that of η though both two phases become deformable with elevated temperature. Moreover, the evaluated thermoelastic anisotropies suggest η′ and η are essentially elastic isotropic on {0001} plane, while η′ exhibit serious mechanical anisotropy and angular bonding characters on both {10-10} and {01–10} planes at high temperature.

The 2D Debye length: An analytical study of weak charge screening in 2D semiconductors

Abstract: Simple perturbations (such as a line charge or a sheet charge) in 2D semiconducting materials create difficult solutions to the Poisson equation due to the non-uniform out-of-plane electric fields that result from the perturbative charge. Here, for the first time, we determine simple and general analytical expressions for the potential profile, its Fourier representation, the corresponding 2D Debye screening length, and the charge screening behavior in 2D semiconductors due to a line charge perturbation. In contrast to conventional 3D semiconductors, we find that the 2D Debye length goes as 1 / N D , 2 D, where N D , 2 D is the 2D semiconductor doping density, and this leads to markedly different Debye lengths as compared to those determined by the conventional (3D) Debye length expression. We show that the potential profile due to a charge perturbation in a 2D semiconductor does not decay exponentially with distance from the perturbation (as is the case for 3D semiconductors) but instead decays logarithmically in the immediate vicinity of the perturbation and as 1 / x 2 when the distance is approximately equal to or greater than the 2D Debye length. Overall, this work establishes an analytical approach for determining a fundamental electrostatic parameter for 2D semiconductors.

Behavioral Modeling of Complex Magnetic Permeability With High-Order Debye Model and Equivalent Circuits

Abstract: In this article, a systematic procedure to derive equivalent circuit networks accurately reproducing the frequency response of the input impedance of magnetic cores in a broad frequency range is presented. The proposed procedure foresees to represent the effective complex permeability spectra of a magnetic core (i.e., the permeability resulting from the superposition of intrinsic material properties and effects due to structural features of the core) by a high-order Debye series expansion, which is subsequently synthesized into suitable Foster and Cauer networks. Such networks can be implemented in any circuit simulator, and are particularly favorable for time-domain transient simulation since they can be easily combined with hysteresis models. Two nanocrystalline tape-wound cores and a commercial bulk current injection probe are used as test cases to prove the effectiveness of the proposed method both in terms of accuracy and ease of implementation.

Charged dielectric spheres interacting in electrolytic solution: A linearized Poisson–Boltzmann equation model

Abstract: We present an analytical theory of electrostatic interactions of two spherical dielectric particles of arbitrary radii and dielectric constants, immersed into a polarizable ionic solvent (assuming that the linearized Poisson–Boltzmann framework holds) and bearing arbitrary charge distributions expanded in multipolar terms. The presented development entails a novel two-center re-expansion analytical theory that expands upon and improves the existing ones, bypassing the conventional expansions in modified Bessel functions. On this basis, we develop a specific matrix formalism that facilitates the construction of asymptotic expansions in ascending order of Debye screening terms of potential coefficients, which are then employed to find exact closed-form expressions for the total electrostatic energy. In particular, this work allows us to explicitly and precisely quantify the k-screened terms of the potential coefficients and mutual interaction energy. Specific cases of monopolar and dipolar distributions are described in particular detail. Comprehensive numerical examples and tests of series convergence and the relative balance of leading and higher-order terms of the mutual interaction energy are presented depending on the inter-particle distance and particles’ radii. The results of this work find application in soft matter modeling and, in particular, in computational biophysics and colloid science, where the availability of increasingly larger experimental structures at the atomic-level resolution makes numerical treatment challenging and calls for more efficient expressions and an increased range of validity.

Dielectric friction, violation of the Stokes-Einstein-Debye relation, and non-Gaussian transport dynamics of dipolar solutes in water

Abstract: The authors explore the coupling between rotations and translations through electrostatic interactions with the medium and show that it leads to non-Gaussian translational dynamics and violation of Stokes-Einstein-Debye relation.

Thermodynamics of Linear Carbon Chains.

Abstract: Linear carbon chains (LCCs) are one-dimensional materials with unique properties, including high Debye temperatures and restricted selection rules for phonon interactions Consequently, their Raman C-band frequency's temperature dependence is a probe to their thermal properties, which are well described within the Debye formalism even at room temperatures Therefore, with the basis on a semiempirical approach we show how to use the C band to evaluate the LCCs' internal energy, heat capacity, coefficient of thermal expansion, thermal strain, and Gruneisen parameter, providing universal relations for these quantities in terms of the number of carbons atoms and the temperature

Effective Debye relaxation models for binary solutions of polar liquids at terahertz frequencies.

Abstract: There are many effective medium models that accurately describe the dielectric properties of mixtures However, these models assume that the components are non-interacting This assumption is not valid for solutions of polar liquids, resulting in significant deviations between the measured and theoretically predicted values of the complex index of refraction of the mixtures We present three effective medium theories by expanding the well-known Debye relaxation model for solutions of polar liquids in the terahertz (THz) regime The new effective medium models proposed in this paper predict the individual relaxation Debye parameters based on the cooperative motion dynamics and self-associative properties of each mixture, and therefore explain the deviation of the dielectric functions of the solutions from the traditional effective medium models These models are verified through reflection measurements of four alcohol-water solutions acquired through THz time-domain spectroscopy (THz-TDS) Compared to the current mixed medium models, the new effective Debye theorem predicts the dielectric properties of polar solutions more accurately and has the potential to explain inter-species mixing schemes and interactions

Understanding degeneracy of two-point correlation functions via Debye random media.

Abstract: It is well known that the degeneracy of two-phase microstructures with the same volume fraction and two-point correlation function S_{2}(r) is generally infinite. To elucidate the degeneracy problem explicitly, we examine Debye random media, which are entirely defined by a purely exponentially decaying two-point correlation function S_{2}(r). In this work, we consider three different classes of Debye random media. First, we generate the "most probable" class using the Yeong-Torquato construction algorithm [Yeong and Torquato, Phys. Rev. E 57, 495 (1998)1063-651X10.1103/PhysRevE.57.495]. A second class of Debye random media is obtained by demonstrating that the corresponding two-point correlation functions are effectively realized in the first three space dimensions by certain models of overlapping, polydisperse spheres. A third class is obtained by using the Yeong-Torquato algorithm to construct Debye random media that are constrained to have an unusual prescribed pore-size probability density function. We structurally discriminate these three classes of Debye random media from one another by ascertaining their other statistical descriptors, including the pore-size, surface correlation, chord-length probability density, and lineal-path functions. We also compare and contrast the percolation thresholds as well as the diffusion and fluid transport properties of these degenerate Debye random media. We find that these three classes of Debye random media are generally distinguished by the aforementioned descriptors, and their microstructures are also visually distinct from one another. Our work further confirms the well-known fact that scattering information is insufficient to determine the effective physical properties of two-phase media. Additionally, our findings demonstrate the importance of the other two-point descriptors considered here in the design of materials with a spectrum of physical properties.