High temperature equation of state of metallic hydrogen

The equation of state of liquid metallic hydrogen is solved numerically. Investigations are carried out at temperatures from 3000 to 20 000 K and densities from 0.2 to 3 mol/cm³, which correspond both to the experimental conditions under which metallic hydrogen is produced on earth and the conditions in the cores of giant planets of the solar system such as Jupiter and Saturn. It is assumed that hydrogen is in an atomic state and all its electrons are collectivized. Perturbation theory in the electron-proton interaction is applied to determine the thermodynamic potentials of metallic hydrogen. The electron subsystem is considered in the randomphase approximation with regard to the exchange interaction and the correlation of electrons in the local-field approximation. The proton-proton interaction is taken into account in the hard-spheres approximation. The thermodynamic characteristics of metallic hydrogen are calculated with regard to the zero-, second-, and third-order perturbation theory terms. The third-order term proves to be rather essential at moderately high temperatures and densities, although it is much smaller than the second-order term. The thermodynamic potentials of metallic hydrogen are monotonically increasing functions of density and temperature. The values of pressure for the temperatures and pressures that are characteristic of the conditions under which metallic hydrogen is produced on earth coincide with the corresponding values reported by the discoverers of metallic hydrogen to a high degree of accuracy. The temperature and density ranges are found in which there exists a liquid phase of metallic hydrogen.     

Metallization degree of hydrogen at a pressure of 1.4 Mbar and a temperature a 3000 K

The electrical resistivity of liquid metallic hydrogen at a temperature of 3000 K and a density of 0.35 mol/cm³ is calculated. Hydrogen is considered as a three-component system consisting of electrons, protons, and neutral hydrogen atoms. The second order of perturbation theory in electron-proton and electron-atom interactions is used to determine the inverse relaxation time for electric conductivity. The Coulomb electron-electron interaction is taken into account in the random phase approximation and the exchange interaction and correlation of conductivity electrons are included in the local-field approximation. The model of hard spheres is used for the proton and atomic subsystems. The concentration of the electrically neutral atomic component proved to be significantly lower than the value assumed by the discoverers of metallic hydrogen.     

Effect of atomic hydrogen adsorption on the transport characteristics of semiconducting carbon nanotubes

The effect of atomic hydrogen adsorption on the conduction and diffusion properties of carbon nanotubes of zigzag type in an external electric field is considered. The model of adsorption of atomic hydrogen on the surface of single-walled carbon nanotubes of zigzag type is based on the single-impurity periodic Anderson model. The theoretical calculation of the diffusion coefficient and electrical conductivity of carbon nanotubes of zigzag type doped with hydrogen atoms is carried out in the relaxation time approximation. It has been revealed that the electrical conductivity and electron diffusion coefficient decrease with increasing concentration of adsorbed hydrogen atoms. It has been shown that the dependence of the electrical conductivity and the diffusion coefficient on the amplitude of the constant electric field at the constant concentration of hydrogen adatoms is nonlinear.     

Effects of absorbed hydrogen on the electronic properties of (Zr2Fe)(1-x)H(x) metallic glasses

The electrical conductivity (σ) of hydrogen doped (Zr(2)Fe)(1-x)H(x) metallic glasses has been measured in the temperature range from 290 down to 5 K. The decrease of the room temperature conductivity and the increase of its temperature coefficient are explained as consequences of increased disorder due to hydrogen doping. σ(T) for (Zr(2)Fe)(1-x)H(x) metallic glasses at low temperatures decreases with the increase of temperature, forming a minimum at T(min), before it starts a monotonic increase with increasing temperature. Both the functional forms and the magnitudes of the observed σ(T) are interpreted in terms of weak localization, electron-electron interaction and spin-fluctuation effects. Our results reveal that the electron-phonon scattering rate varies with the square of temperature from low temperatures up to 100 K and changes behaviour to a linear form at higher temperatures. At low temperatures, the minimum in σ(T) is shifted to higher temperatures, which is ascribed to the increase of the screening parameter of the Coulomb interaction F* associated with the enhancement of the spin fluctuations arising from the increase of the hydrogen doping. The spin-orbit scattering rate and the electron diffusion constant are reduced by hydrogen doping.     

On the Optical Conductivity of Kondo Insulators

The temperature-dependent optical conductivity of a Kondo insulator for different temperatures with impurity doping on the conduction band is studied within the U = ∞ Anderson lattice model in the framework of a slave-boson mean-field theory under the coherent potential approximation. The results show that the depletion of the optical conductivity in low-frequency region decreases with increasing of the temperature, and the system exhibits a transition between a low-temperature insulating phase and a high-temperature metallic phase. With increasing of the impurity concentration, the effect of the impurity scattering could result in a nearly temperature-independent gap behavior. The numerical results on the localization of the electron and its variation with temperature are also discussed with the help of optical sum rule.     

Electronic structure model of a metal-filled carbon nanotube

Carbon monolayer nanotubes filled with K, Rb, and Cs atoms, in which every ten carbon atoms captures an electron from the doping atoms, are considered. It is assumed that a positive charge in the bulk of the nanotube and a negative charge on its surface are distributed uniformly so that the potential energy of a conduction electron inside the nanotube is proportional to the square of the distance to its center. The dependences of the Fermi quasi-momentum for conduction electrons inside the nanotube on their volume density and the tube radius are obtained in the one-electron approximation for an arbitrary number of subbands of transverse motion. The Landauer formula is used for calculating the dependence of the conductivity of the metallic subsystem of the nanotube on its radius.     

Conductivities in Hot Aluminium Plasma

We perform model calculations for the electrical and thermal conductivity of aluminium plasma within the generalized linear response method of Zubarev for temperatures of (5–25) eV and densities of (0.01–10) g/cm³. The composition in the expanded plasma region is determined by considering higher ionization states up to 5+ and solving the respective system of coupled mass action laws. Besides this chemical picture, a generalized Thomas‐Fermi model is applied to calculate the equation of state and the average charge state of the ions for densities near and above solid state density. Interactions between the various species are treated on T matrix level. Numerical results for the electrical and thermal conductivity of aluminium plasma are compared with experimental data and, for high densities, also with results of a Born approximation with respect to a weak electron‐ion pseudopotential.     

Electrical conductivity and thermopower of metallic helium

The pair effective interionic interaction, electrical resistance, and thermopower of liquid metallic helium have been calculated over wide temperature and density ranges using the perturbation theory for the potential of electron-ion interaction. For conduction electrons, the random-phase approximation has been used taking into account the exchange interaction and correlations in the local-field approximation. The nuclear subsystem has been described by the hard-sphere model. The sphere diameter is the only parameter of the theory. The diameter and the system density at which helium is transformed from the singly ionized to doubly ionized state have been estimated based on an analysis of the pair effective interaction between helium nuclei. The case of doubly ionized helium atoms has been considered. The numerical calculations have been performed taking into account the perturbation theory in terms up to the third order. In all cases, the role of the third-order correction is significant. In the case of metallic helium, the values of the electrical resistance and its temperature dependence are characteristic of divalent simple liquid metals, as well as the dependences of the thermopower on the density and temperature.     

Equation of state of metallic helium

The effective ion-ion interaction, free energy, pressure, and electric resistance of metallic liquid helium have been calculated in wide density and temperature ranges using perturbation theory in the electron-ion interaction potential. In the case of conduction electrons, the exchange interaction has been taken into account in the random-phase approximation and correlations have been taken into account in the local-field approximation. The solid-sphere model has been used for the nuclear subsystem. The diameter of these spheres is the only parameter of this theory. The diameter and density of the system at which the transition of helium from the singly ionized to doubly ionized state occurs have been estimated by analyzing the pair effective interaction between helium atoms. The case of doubly ionized helium atoms has been considered. Terms up to the third order of perturbation theory have been taken into account in the numerical calculations. The contribution of the third-order term is significant in all cases. The electric resistance and its temperature dependence for metallic helium are characteristic of simple divalent metals in the liquid state. The thermodynamic parameters—temperature and pressure densities-are within the ranges characteristic of the central regions of giant planets. This makes it possible to assume the existence of helium in the metallic state within the solar system.     

Electrical conductivity of Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O ferromagnetic films at low temperatures

The results of experiments on electrical conductivity and magnetic properties of thin cobalt-doped zinc oxide films are reported. The results indicate the predominance of the hoping conduction mechanism at low temperatures and the band mechanism at high temperatures. An increase in the cobalt concentration from 1.5 to 6.3 at % leads to the reduction of the electrical conductivity of the films. The contribution of hopping conduction to the conductivity increases due to a decrease in the crystallinity of the films and localization of a part of electron states upon an increase in the cobalt concentration. For cobalt-containing films, a hysteresis of the magnetic moment as a function of the magnetic field is observed. The dependence of the shape of the magnetization curves on the cobalt concentration is irregular. The paramagnetic contribution to the magnetic susceptibility increases with the cobalt concentration.     

Temperature and concentration dependences of the electrical resistivity for alloys of plutonium with americium under normal conditions

The temperature and concentration dependences of the electrical resistivity for alloys of americium with plutonium are analyzed in terms of the multiband conductivity model for binary disordered substitution-type alloys. For the case of high temperatures (T > Θ_D, Θ_D is the Debye temperature), a system of self-consistent equations of the coherent potential approximation has been derived for the scattering of conduction electrons by impurities and phonons without any constraints on the interaction intensity. The definitions of the shift and broadening operator for a single-electron level are used to show qualitatively and quantitatively that the pattern of the temperature dependence of the electrical resistivity for alloys is determined by the balance between the coherent and incoherent contributions to the electron-phonon scattering and that the interference conduction electron scattering mechanism can be the main cause of the negative temperature coefficient of resistivity observed in some alloys involving actinides. It is shown that the great values of the observed resistivity may be attributable to interband transitions of charge carriers and renormalization of their effective mass through strong s-d band hybridization. The concentration and temperature dependences of the resistivity for alloys of plutonium and americium calculated in terms of the derived conductivity model are compared with the available experimental data.     

Hydrogen-induced surface metallization of SrTiO3(001)

Surface metallization of SrTiO3(001) by hydrogen adsorption is experimentally confirmed for the first time by photoemission spectroscopy and surface conductivity measurements. The metallic state is assigned to a quantized state in the space-charge layer induced by electron doping from hydrogen atoms. The measured two-dimensional (2D) conductivity is well above the 2D Ioffe-Regel limit indicating that the system is in a metallic conduction regime. The mean free path of the surface electron is estimated to be several nanometers at room temperature.     

Nature of EPR line asymmetry in La<Subscript>0.70</Subscript>Ca<Subscript>0.25</Subscript>Ba<Subscript>0.05</Subscript>MnO<Subscript>3</Subscript>

It was pointed out in some works that asymmetry of an electron paramagnetic resonance (EPR) line is generally caused by both the electrical conduction and the nondiagonal elements of the dynamic susceptibility of a magnetic subsystem. Direct measurements of the temperature dependences of the conductivity and the EPR line shape in a La_0.70Ca_0.25Ba_0.05MnO₃ sample showed that the conduction makes the predominant contribution to the EPR line asymmetry.     

Electrical conductivity of multi-layered metallic thin films

Multi-layered metallic thin films have quite unique properties such as electrical conductivity because of their enhanced interactions at the interfaces between different metals. A theoretical solution has been derived for the distribution functions of the conduction electrons, through Boltzmann's equation and certain interface boundary conditions. The solution of the electrical conductivity for the multi-layered metallic thin films is given.     

Effective proton-proton interaction and metallization of hydrogen

The effective proton-proton interaction in metallic hydrogen has been calculated for various densities. In the potential of this interaction, which can be represented in the form of a series of perturbation theory in the electron-proton interaction, the second- and third-order terms are taken into account. The second-order term gives a comparatively shallow potential well with one minimum. The position of the minimum corresponds to the equilibrium mutual position of protons in metallic hydrogen. When the third-order term is additionally taken into account, the potential has two characteristic minima; the position of one of them corresponds to the distance between the protons in a hydrogen molecule. The depths of these potential wells depend on the density of the system. At fairly high densities, only the potential well corresponding to the equilibrium position of protons in the metallic phase holds in the proton-proton potential. Owing to the presence of two minima in the effective proton-proton potential, the density of hydrogen at the point of transition to the metallic state can be estimated. Analysis of the effective proton-proton interaction makes it also possible to estimate the possibility of the existence of metallic hydrogen in a stable state at quite low temperatures.     

Scattering of low-energy atoms by metallic surfaces

The problem of a neutral low-energy atom impinging on a well-defined metallic surface is approached from first principles. The solid and its potential energy of interaction with the incident atom is treated in the most general way, but under the following assumptions: (a) the conduction electrons interact adiabatically with the lattice ions and the gas atom; (b) no chemical reactions occur; (c) the one-phonon approximation is valid. The scattering amplitudes for surface and bulk mode excitations are obtained in terms of the dynamical properties of the metallic surface. Direct collisions of the incident atoms with the lattice ions are shown to give a negligible contribution to the scattering. The most important contribution comes from the interaction of the gas atom with the surface conduction electrons; the excitation of lattice vibrational modes occurs through the electron-phonon term of the Hamiltonian. The general expressions for the scattering amplitudes obtained show that the scattering is incoherent. With further assumptions one obtains a separation of the scattering amplitude into a coherent and incoherent part.     

Ac conductivity in boron doped amorphous carbon films

Experimental results on frequency and temperature dependence of ac conduction in boron doped amorphous carbon films are analyzed in the framework of available microscopic models. Depending on the response, the conductivity plot is divided into three regimes (low frequency high temperature; moderate frequency intermediate temperature; high frequency low temperature) and the data in the respective regimes are corroborated with the various theoretical models accordingly. The conductivity data at high frequency and low temperature suggests that relaxation via quantum mechanical tunneling might be the dominant conduction mechanism. At intermediate temperatures and moderate frequencies, the conductivity data is in good agreement with extended pair approximation model with interaction correction. Signature of enhanced interaction effect is observed at low temperature.     

Diffusion of hydrogen and oxygen in the high temperature proton conductor srceo3 investigated by dynamic conductivity measurements

In SrCeO₃ the oxygen vacancy concentration at elevated temperatures depends on the oxygen partial pressure in the surrounding atmosphere. Changes of the oxygen vacancy concentration are accompanied by change in the hole concentration and therefore can be measured by electrical conductivity measurements. We apply a dynamic method for studying the diffusion of oxygen vacancies by measurements of the time dependence of the electrical conduction after a sudden change in the oxygen partial pressure has taken place.

In doped samples and under wet conditions the protonic charge carriers are mainly incorporated by a dissociative absorption of water and lead to a noticeable protonic conduction. The proton diffusion in SrCe_0.95 Y_0.05O₃ is determined by relaxation measurements at a polarised sample in wet and hydrogen containing atmosphere. The electrochemical cell discussed here is characterised by a combination of one reversible and one (hydrogen) ion blocking electrode. From the time dependence of the depolarisation process the hydrogen diffusivity is extracted.     

强激光照射对6H-SiC晶体电子特性的影响

使用基于密度泛函微扰理论的第一性原理赝势法, 模拟研究了纤锌矿6H-SiC晶体在强激光照射下电子特性的变化. 研究结果表明, 电子温度T_e在升高到3.89 eV及以上后, 6H-SiC由间接带隙的晶体变为直接带隙的晶体; 带隙值随电子温度T_e升高先是增大后又快速减小, 当电子温度T_e大于4.25 eV以后, 带隙已经消失而呈现出金属特性.