bluuebunny/crossref_metadata_2025_split huggingface dataset:
Improved analytical approximation to arbitrary l‐state solutions of the Schrödinger equation for the hyperbolical potentials
Authors: Ikhdair S.M. , Sever R. 
Published: June 2022

AbstractThe Schrödinger equation for the rotational‐vibrational (ro‐vibrational) motion of a diatomic molecule with empirical potential functions is solved approximately by means of the Nikiforov‐Uvarov method. The approximate energy spectra and the corresponding normalized total wavefunctions are calculated in closed form and expressed in terms of the hypergeometric functions or Jacobi polynomials Pn(μ, ν) (x), where μ >−1, ν >−1 and x in [−1, +1]. The s‐waves analytic solution is obtained. The numerical energy eigenvalues for selected H2 and Ar2 molecules are also calculated and compared with the previous models and experiments.
Reduction of quantum fluctuations by anisotropy fields in Heisenberg ferro‐ and antiferromagnets
Authors: Vogt B. , Kettemann S. 
Published: June 2022

AbstractThe physical properties of quantum systems, which are described by the anisotropic Heisenberg model, are influenced by thermal as well as by quantum fluctuations. Such a quantum Heisenberg system can be profoundly changed towards a classical system by tuning two parameters, namely the total spin and the anisotropy field: Large easy‐axis anisotropy fields, which drive the system towards the classical Ising model, as well as large spin quantum numbers suppress the quantum fluctuations and lead to a classical limit. We elucidate the incipience of this reduction of quantum fluctuations. In order to illustrate the resulting effects we determine the critical temperatures for ferro‐ and antiferromagnets and the ground state sublattice magnetization for antiferromagnets. The outcome depends on the dimension, the spin quantum number and the anisotropy field and is studied for a widespread range of these parameters. We compare the results obtained by: Classical Mean Field, Quantum Mean Field, Linear Spin Wave and Random Phase Approximation. Our findings are confirmed and quantitatively improved by numerical Quantum Monte Carlo simulations. The differences between the ferromagnet and antiferromagnet are investigated. We finally find a comprehensive picture of the classical trends and elucidate the suppression of quantum fluctuations in anisotropic spin systems. In particular, we find that the quantum fluctuations are extraordinarily sensitive to the presence of small anisotropy fields. This sensitivity can be quantified by introducing an “anisotropy susceptibility”.
Effect of electric field on diffusion in disordered materials
Authors: Jansson F. , Nenashev A.V. , Baranovskii S.D. , Gebhard F. , Österbacka R. 
Published: June 2022

AbstractThe effect of electric field on diffusion of charge carriers in disordered materials is studied by Monte Carlo computer simulations and analytical calculations. It is shown how an electric field enhances the diffusion coefficient in the hopping transport mode. The enhancement essentially depends on the temperature and on the energy scale of the disorder potential. It is shown that in one‐dimensional hopping the diffusion coefficient depends linearly on the electric field, while for hopping in three dimensions the dependence is quadratic.
Localization of excitons in weakly disordered semiconductor structures: A model study
Authors: Gögh N. , Thomas P. , Kuznetsova I. , Meier T. , Varga I. 
Published: June 2022

AbstractLocalization of the center‐of‐mass (com) motion of an exciton in a disordered semiconductor structure is studied theoretically by focusing on nonlinear optical spectroscopy. A one‐dimensional tight‐binding model with diagonal disorder is applied and the Coulomb interaction is treated consistently. In the ordered situation the center‐of‐mass momentum (K) selection rule leads to only the lowest transition for K = 0. The break down of the com‐K‐selection rule produces the well known asymmetric excitonic lines of disordered semiconductors. The coupling between the lowest dominant transition to this modified com‐continuum yields Fano‐like features in the nonlinear spectra.
Application of the photon's intrinsic flux to the 1s‐2p and 2p‐3d excitonic transitions in nanostructures
Authors: Saglam Z. , Saglam M. 
Published: June 2022

AbstractWe have applied our two recent results [depending on its helicity photon carries a quantum flux of ± Φ 0 = ± hc/e and the quantized magnetic fluxes through the electronic orbits of the Dirac hydrogen atom are given by: Φ (n,l,mj) = (n‐l‐mj)Φ0) ] to the 1s‐2p and 2p‐3d excitonic transitions in nanostructures. It is shown that the flux changes for the non‐zero matrix elements in the 1s‐2p and 2p‐3d excitonic transitions is either ± Φ0 or zero. The present result supports the previous results stated above. It is also shown that spin flip is possible in the 1s‐2p and 2p‐3d excitonic transitions.
Conductance asymmetry of a slot gate Si‐MOSFET in a strong parallel magnetic field
Authors: Shlimak I. , Golosov D.I. , Butenko A. , Friedland K.‐J. , Kravchenko S.V. 
Published: June 2022

AbstractWe report measurements on a Si‐MOSFET sample with a slot in the upper gate, allowing for different electron densities n1,2 across the slot. The dynamic longitudinal resistance was measured by the standard lock‐in technique, while maintaining a large DC current through the source‐drain channel. We find that the conductance of the sample in a strong parallel magnetic field is asymmetric with respect to the DC current direction. This asymmetry increases with magnetic field. The results are interpreted in terms of electron spin accumulation or depletion near the slot.
Angular and temperature‐related specific features of averaging of hole effective masses in p‐Ge at low temperatures
Authors: Tisnek T. , Veinger A. , Zabrodskii A. , Goloshchapov S. 
Published: June 2022

AbstractMicrowave magnetoresistance of lightly doped (nondegenerate) p‐Ge has been studied by the electron spin resonance method, which can record the derivative of the microwave absorption with respect to the magnetic field. The change in the absorption is proportional to that in the conductivity of the semiconductor in the magnetic field (magnetoresistance). It was found that the averaging time of the light and heavy holes effective masses depends on temperature and on the magnetic field direction in a sample. An analysis of the derivative made it possible to determine regions of the fastest effective mass averaging.
Lattice distortion (Peierls Transition) caused by spin interaction in the chaotic impurity system of a semiconductor
Authors: Zabrodskii A. , Veinger A. , Tisnek T. , Goloshchapov S. 
Published: June 2022

AbstractThe effect of an elastic spontaneous distortion of the crystal lattice of a doped semiconductor Ge:As near the insulator–metal (IM) phase transition has been discovered. The effect is manifested in the electron spin resonance (ESR) of neutral As atoms as a splitting of the single resonance absorption line. It observed at electron concentrations in the range 0.8 < n/nC < 1 at low temperatures T < 100 K (nC = 3.7 × 1017 cm‐3 is the critical electron concentration for the IM phase transition). The splitting is the strongest along each of the six [110] directions, which indicates that the local lattice distortion occurs just in these directions. As a result, a sample is possibly divided into separate domains differing in the directions of compressive or tensile deformations. A study of concentration, temperature, and angular dependences of the effect has shown that the phenomenon discovered can be understood in terms of the Peierls spin transition model.
Calculation of profile of charge carrier concentration in modulation doped structure with a wide potential well
Authors: Shchurova L.Yu. 
Published: June 2022

AbstractWe investigate the equilibrium state of interacting electron system with Fermi statistics in modulation doped structure with a wide quantum well. The model is formulated for the carrier system with a sufficiently high density, such that the de Broglie wavelength of electrons is smaller than the width of the quantum well. Due to a significant interaction of electrons with electric field of the doped layer, a state with strongly‐inhomogeneous density of electrons is formed. Within the hydrodynamic approach, we set up formalism for calculating the electron density across the width of the potential well. We have obtained the exact solution of the equations, which is expressed in terms of hypergeometric functions. Based on the deduced formulas, we performed numerical computations for the profile of carriers' concentrations in a potential well in the modulation doped Si/SiGe/Si structures.
Localised magneto‐optical collective excitations of impure graphene
Authors: Fischer A.M. , Dzyubenko A.B. , Römer R.A. 
Published: June 2022

AbstractWe study optically‐induced collective excitations of graphene in the presence of a strong perpendicular magnetic field and a single impurity. We determine the energies and absorption strengths of these excitations, which become localised on the impurity. Two different types of impurity are considered i. the long‐range Coulomb impurity, ii. a δ‐function impurity located at either an A or B graphene sublattice site. Both impurity types result in some bound states appearing both above and below the magnetoplasmon continuum, although the effect of the short‐range impurity is less pronounced. The dependence of the energies and oscillator strengths of the bound states on the filling factor is investigated.
Quadrupolar glass as a model for charge carrier transport in nonpolar organic materials
Authors: Novikov S.V. 
Published: June 2022

AbstractMonte Carlo simulation of the charge carrier transport in disordered nonpolar organic materials has been carried out. As a suitable model we considered the model of quadrupolar glass. A general formula for the temperature and field dependence of the mobility was suggested. A comparison with experimental data has been carried out.
The dependence of polymer conductivity on the work function of metallic electrodes
Authors: Ionov A.N. , Dunaevskii M.S. , Nikolaeva M.N. , Rentzsch R. 
Published: June 2022

AbstractIt is shown that the occurrence of metallic conductivity in polymers is due to their electrification. In particular, the current density depends on the electron work function of metallic electrodes which are in contact with the polymer.
Pair and impair, even and odd form fields, and electromagnetism
Authors: da Rocha R. , Rodrigues W.A. 
Published: June 2022

AbstractIn this paper after reviewing the Schouten and de Rham definition ofimpairandpairdifferential form fields (not to be confused with differential form fields of even and odd grades) we prove that in arelativistic spacetimeit is possible (despite claims in contrary) to coherently formulate electromagnetism (and we believe any other physical theory) using only pair form fields or, if one wishes, using pair and impair form fields together, in an appropriate way. Those two distinct descriptions involve only a mathematical choice and do not seem to lead to any observable physical consequence if due care is taken. Moreover, we show in details that a formulation of electromagnetic theory in the Clifford bundle formalism of differential forms where the two Maxwell equations of the so called metric‐free approach becomes a single equation is compatible with both formulations of electromagnetism just mentioned above. In addition we derive directly from Maxwell equation the density of force (coupling of the electromagnetic field with the charge current) that is a postulate in the free metric approach to electromagnetism. We recall also a formulation of the engineering version of Maxwell equations using electric and magnetic fields as objects of the same nature, i.e., without using polar and axial vectors.
An electric charge has no screw sense – a comment on the twistfree formulation of electrodynamics by da Rocha and Rodrigues
Authors: Itin Y. , Obukhov Yu.N. , Hehl F.W. 
Published: June 2022

AbstractDa Rocha and Rodigues (RR) claim (i) that in classical electrodynamics in vector calculus the distinction between polar and axial vectors and in exterior calculus between twisted and untwisted forms is inappropriate and superfluous, and (ii) that they can derive the Lorentz force equation from Maxwell's equations. As to (i), we point out that the distinction of polar/axial and twisted/untwisted derives from the property of the electric charge of being a pure scalar, that is, not carrying any screw sense. Therefore, the mentioned distinctions are necessary ingredients in any fundamental theory of electrodynamics. If one restricted the allowed coordinate transformations to those with positive Jacobian determinants (or prescribed an equivalent constraint), then the RR scheme could be accommodated; however, such a restriction is illegal since electrodynamics is, in fact, also covariant under transformations with negative Jacobians. As to (ii), the “derivation” of the Lorentz force from Maxwell's equations, we point out that RR forgot to give the symbol F (the field strength) in Maxwell's equations an operational meaning in the first place. Thus, their proof is empty. Summing up: the approach of RR does not bring in any new insight into the structure of electrodynamics.
Broad band electromagnetic wave absorbers designed with nano‐metal films
Authors: Nimtz G. , Panten U. 
Published: June 2022

AbstractIn the thirties of the last century it was shown that nano‐metal films have a frequency independent absorption in the far infrared regime and below. Moreover, the absorption A of these films is 0.5 and at the same time both reflection R and transmission T are 0.25, complying with the relation A + R + T = 1 at a sheet resistance Z□of 60 πΩ. The latter property of nano‐metal films was shown by Woltersdorff in 1934. Multiple reflections between such films allow the design of low reflecting large scale absorbers for the wave length range from far infrared to low frequency radio waves. Experimental data of the novel absorber device measured in the GHz frequency range are presented. The electrical nano‐metal film properties are also useful for applications in IR‐photonics and IR‐communication systems. The article presents a brief review of the historical studies on free carrier electromagnetic wave absorption and on novel applications.
Transport through a Kondo quantum dot: Functional RG approach
Authors: Schmidt H. , Wölfle P. 
Published: June 2022

AbstractWe apply the functional renormalization group (FRG) method to calculate the conductance of a quantum dot in the Kondo regime. Starting from the exact FRG equations in Keldysh formulation for the Kondo exchange Hamiltonian in pseudo‐fermion (pf) representation, we solve the coupled equations for the pf self energy and the coupling function, neglecting three‐particle and higher correlation functions. The conductance G as a function of temperature T and bias voltage V is calculated using a renormalized Golden Rule expression. The limiting behavior at T and/or V >> TK (TK: Kondo temperature) agrees with known results. The difficulties when approaching strong coupling are analyzed and improvements are suggested.
Manifestly covariant classical correlation dynamics II. Transport equations and Hakim equilibrium conjecture
Authors: Tian C. 
Published: June 2022

AbstractThis is the second of a series of papers on special relativistic classical statistical mechanics. Employing the general theory developed in the first paper, we derive rigorously the relativistic Vlasov, Landau, and Boltzmann equations, respectively. The latter two equations advocate the Jüttner distribution as the equilibrium distribution. We thus, at the fully microscopic level, provide support for the recent numerical findings of Cubero and co‐workers of the special relativistic generalization of the Maxwell‐Boltzmann distribution. Furthermore, the present theory allows us to calculate rigorously various correlation functions at the relativistic many‐body equilibrium. Therefore, we demonstrate that the relativistic many‐body equilibrium conjecture of Hakim is justified.
Spatial Wilson loop in continuum, deconfining SU(2) Yang‐Mills thermodynamics
Authors: Ludescher J. , Keller J. , Giacosa F. , Hofmann R. 
Published: June 2022

AbstractThe uniquess of the effective actions describing 4D SU(2) and SU(3) continuum, infinite‐volume Yang‐Mills thermodynamics in their deconfining and preconfining phases is made explicit. Subsequently, the spatial string tension is computed in the approach proposed by Korthals‐Altes. This SU(2) calculation is based on a particular, effective two‐loop correction to the pressure needed for the extraction of the hypothetic number density of isolated and screened magnetic monopoles or antimonopoles in the deconfining phase. By exponentiating the exchange of the tree‐level massless but one‐loop dressed mode within a quadratic spatial contour of side‐length L in the effective theory we demonstrate that for L → ∞ the Wilson loop exhibits perimeter law. This is in contrast to a rigorous lattice result subject to the Wilson action and for this action valid at sufficiently high temperature. In the framework of the effective theory there is, however, a regime for small (spatially unresolved) L were the exponent of the spatial Wilson loop possesses curvature as a function of L.
The quasiorder‐disorder phase transition and peak effect in MgB2 type‐II superconducting materials and thin films
Authors: Chou M.J. , Horng H.E. 
Published: June 2022

AbstractThe peak effect and the quasiorder‐disorder first‐order phase transition for Magnesium diboride, MgB2, superconducting bulk materials have been studied. The peak values of the critical current density Jc, and the exact peak positions together with its corresponding half‐widths for a constant temperature as well as for a constant applied magnetic field have been calculated by considering the quantum, thermal as well as random fluctuations of the vortex lattice. The results for MgB2 bulk materials are in agreement with the experiment. The peak effect for MgB2 superconducting thin films is also predicted theoretically. The expected peak effect may be observed provided that doping or other experimental techniques are applied to improve the flux pinning of the MgB2 superconducting thin films.
Dmitrij Volkov, super‐Poincaré group and Grassmann variables
Authors: Zheltukhin A.A. 
Published: June 2022

AbstractA fundamental role of the Hermann Grassmann anticommuting variables both in physics and mathematics is discussed on the example of supersymmetry. The talk describes how the D. Volkov question about possibility of the existence of Nambu‐Goldstone fermions, realized by the Grassmannian variables, resulted in the discovery of the super‐Poincaré group, its spontaneous breaking and gauging.
Algebraic geometry approach in gravity theory and new relations between the parameters in type I low‐energy string theory action in theories with extra dimensions
Authors: Dimitrov B.G. 
Published: June 2022

AbstractOn the base of the distinction between covariant and contravariant metric tensor components, a new (multivariable) cubic algebraic equation for reparametrization invariance of the gravitational Lagrangian has been derived and parametrized with complicated non‐elliptic functions, depending on the (elliptic) Weierstrass function and its derivative. This is different from standard algebraic geometry, where only two‐dimensional cubic equations are parametrized with elliptic functions and not multivariable ones. Physical applications of the approach have been considered in reference to theories with extra dimensions. The s.c. “length function” l(x) has been introduced and found as a solution of quasilinear differential equations in partial derivatives for two different cases of “compactification + rescaling” and “rescaling + compactification”. New physically important relations (inequalities) between the parameters in the action are established, which cannot be derived in the case l = 1 of the standard gravitational theory, but should be fulfilled also for that case.
Flavour mixing in an expanding universe
Authors: Tarantino F. 
Published: June 2022

AbstractMotivated by a microscopic model of string‐inspired foam, in which foamy structures are provided by brany point‐like defects (D‐particles) in space‐time, we discuss flavour mixing in curved space‐time for spin‐0 and spin‐1/2 particles. This can be view as the low energy limit of flavour non‐preserving interactions of stringy matter excitations with the defects, and non‐trivial space‐time background induced by quantum fluctuations of the D‐particles. We show, at late epochs of the Universe, that both the fermionic and the bosonic vacuum condensate behaves as a fluid with negative pressure and positive energy; however the equation of state has wfermion > ‐1/3 and therefore the contribution of fermion‐fluid flavour vacuum alone could not yield accelerating Universes. On the other hand, for the boson fluid the equation of state is, for late eras, close to wboson → ‐1, and hence overall the D‐foam universe appears accelerating at late eras.
Fourth‐order braneworld gravity
Authors: Balcerzak A. 
Published: June 2022

AbstractWe discuss a general fourth‐order theory of gravity and formulate the generalized Israel junction conditions for the theory by application of a generalized Gibbons‐Hawking boundary term which is added to the action of the fourth‐order gravity theory. Next, we use the generalized Israel junction condition for the construction of a higher‐order gravity braneworld model.
Constraining sudden future singularity models
Authors: Ghodsi H. , Hendry M.A. 
Published: June 2022

AbstractOne of the key challenges facing cosmologists today is the nature of the mysterious dark energy introduced in the standard model of cosmology to account for the current accelerating expansion of the universe. In this regard, many other non‐standard cosmologies have been proposed which would eliminate the need to explicitly include any form of dark energy. One such model is the Sudden Future Singularity (SFS) model, in which no equation of state linking the energy density and the pressure in the universe is assumed to hold. In this model it is possible to have a blow up of the pressure occurring in the near future while the energy density would remain unaffected. The particular evolution of the scale factor of the Universe in this model that results in a singular behaviour of the pressure also admits acceleration in the current era as required. In this paper we compare an example SFS model with the current data from high redshift supernovae, baryon acoustic oscillations (BAO) and the cosmic microwave background (CMBR). We explore the limits placed on the SFS model parameters by these current data and discuss the viability of the SFS model in question as an alternative to the standard concordance cosmology.
Some spaces are more equal than others
Authors: Roukema B.F. 
Published: June 2022

AbstractIt has generally been thought that in perturbed Friedmann‐Lemaître‐Robertson‐Walker models of the Universe, global topology should not have any feedback effects on dynamics. However, a weak‐field limit heuristical argument, assuming a finite particle horizon for the transmission of gravitational signals, shows that a residual acceleration effect can occur. The nature of this effect differs algebraically between different constant curvature 3‐manifolds. This potentially provides a selection mechanism for the 3‐manifold of comoving space.
(Quantum) gravity effects via exotic ℝ4
Authors: Król J. 
Published: June 2022

AbstractThe arguments are given that exotic smooth ℝ4's can be considered as the natural counterpart for geometry of quantum gravity in some limits. This follows from the relations of these exotics to ℤ2 orientifolds of WZW models on SU(2), abelian gerbes on S3, generalized Hitchin's–Gualtieri structures as well gerbes on some orbifolds. Non‐standard smoothings of ℝ4 seem to carry also quantum information about spacetime and gravity.