Reconstruction of bands in metallic hydrogen

The generalized theory of normal properties of a metal for the case of the properties of the electronic band of electron–phonon systems with a variable electron density of states is used to study the normal phase of metallic hydrogen at a pressure of 500 GPa and a temperature of 200 K. We calculated the frequency dependence of the real ReΣ(ω) and imaginary ImΣ(ω) parts of the self-energy part of the electron Green’s function Σ(ω), as well as the electron density of states N(ε) of the stable phase of metallic hydrogen with the I41/amd symmetry at a pressure of 500 GPa, renormalized by the strong electron–phonon coupling. It is found that the electron conduction band of the I41/amd phase of metallic hydrogen undergoes insignificant reconstruction near the Fermi level because of the renormalization by the electron–phonon coupling.     

Critical temperature of metallic hydrogen sulfide at 225-GPa pressure

The Eliashberg theory generalized for electron—phonon systems with a nonconstant density of electron states and with allowance made for the frequency behavior of the electron mass and chemical potential renormalizations is used to study T _c in the SH₃ phase of hydrogen sulfide under pressure. The phonon contribution to the anomalous electron Green’s function is considered. The pairing within the total width of the electron band and not only in a narrow layer near the Fermi surface is taken into account. The frequency and temperature dependences of the complex mass renormalization ReZ(ω), the density of states N(ε) renormalized by the electron—phonon interactions, and the electron—phonon spectral function obtained computationally are used to calculate the anomalous electron Green’s function. A generalized Eliashberg equation with a variable density of electron states has been solved. The frequency dependence of the real and imaginary parts of the order parameter in the SH₃ phase has been obtained. The value of T _c ≈ 177 K in the SH₃ phase of hydrogen sulfide at pressure P = 225 GPa has been determined by solving the system of Eliashberg equations.     

Activation conduction in metallic island films

The differential conductivity of metallic island films of Ti, Co, W, and FeNi is investigated in the vicinity of liquid nitrogen temperatures. It is found that the temperature dependence of the conductivity of metallic island films in the insulator phase varies in accordance with the activation law σ ∝T ⁿ exp(?E/kT). It is shown that the power of temperature in the preexponential factor varies from n = 2 to 1 upon an increase in the film thickness. In thicker films, in which a transition from the insulator to the metal conductivity phase takes place, the temperature dependence of the conductivity increases in proportion to temperature. The mechanism of conduction in metallic island films is discussed.     

Impurity band conduction in CdHgTe crystals

Electrical conduction at 77 K in Cd_xHg_1−xTe, with the composition x ⩽ 0.2, is by electrons in the conduction band, by holes in the valence band and by holes in the impurity band. In samples with zero energy gap, x < 0.14, electrical conduction by holes in the valence band is comparable to electrical conduction by holes in the impurity band. In the open energy gap CdHgTe, electrical conduction by holes in the valence band is negligible in comparison to electrical conduction by holes in the impurity band. In CdHgTe samples, electrical conduction in the impurity band is described by the “Fermi Glass” model.     

Nonparabolicity and warping in the conduction band of GaAs

The dispersion of the conduction band in GaAs is calculated using k·p models which in different ways take into account the coupling to the p-bonding and p-antibonding states. Nonparabolicity, warping and spin-splitting are accurately described up to energies about 50 meV above the conduction band minimum by the 8×8 Kane model. For higher energies a 14×14 matrix is required.     

Three-dimensional confinement in the conduction band structure of InP

Strong quantum confinement in InP is observed to significantly reduce the separation between the direct and indirect conduction band states. The effects of three-dimensional confinement are investigated by tailoring the initial separation between conduction band states using quantum dots (QDs) of different sizes and hydrostatic pressure. Analyses of the QD emission spectra show that the X(1c) states are lowest in energy at pressures of approximately 6 GPa, much lower than in the bulk. The transition to the X(1c) states can be explained by either a sequence of gamma-L and L-X crossings, or by the crossover between strongly coupled gamma and X states.     

Surface states in the conduction band region of Si

The energy distribution of surface states within the conduction band has been determined analizing the mobility ratio μ_H/μ_eff. A shallow trap model was used to describe the surface states.     

Franck-Condon distribution in the 226 nm band of trimethylene sulfide

The potential function for the ring-puckering vibration of trimethylene sulfide in the lowest excited singlet state is obtained, and the relative intensity distribution in the 226 nm electronic transition calculated. It is concluded that the excitation of the ring-puckering vibration by itself does not account for the intensity of the higher energy peaks that are better assigned as combination bands of ring-puckering and CS stretching modes.     

Anderson impurity in a correlated conduction band

We investigate the physics of a magnetic impurity with spin 1/2 in a correlated metallic host. Describing the band by a Hubbard Hamiltonian, the problem is analyzed using dynamical mean-field theory in combination with Wilson's nonperturbative numerical renormalization group. We present results for the single-particle density of states and the dynamical spin susceptibility at zero temperature. New spectral features (side peaks) are found which should be observable experimentally. In addition, we find a general enhancement of the Kondo scale due to correlations. Nevertheless, in the metallic phase, the Kondo scale always vanishes exponentially in the limit of small hybridization.     

On the probability distribution of conduction states in metallic nanowires

For the first time, a mathematical analysis on the probability distribution of conduction states in metallic nanowires is presented starting from the well-known Lorentzian-like model relative to the electrical conductance through both resonant and off-resonant states in metal contacts at nanometer scale. The main aspects related to the corresponding probability-density function are discussed. In particular, probability density at quasi-resonance is determined.     

Electric conduction in n-type germanium and cadmium sulfide

The impurity conduction of n-type Ge and CdS is calculated via a previously developed theory for impurity bands in doped semiconductors. Rough agreement with experimental data over a wide range of impurity concentration is found. The comparison with AMO-MT calculation shows a large enhancement due to a stronger electron correlation.     

Pressure-broadened linewidths of hydrogen sulfide

Self-broadened and foreign-gas (N₂ and O₂) broadened linewidths of H₂S at 300°K have been calculated using the Anderson-Tsao-Curnutte theory of line broadening for a wide range of quantum numbers J and K_a, in both type A and type B bands. Computed values for self-broadened linewidths are in good agreement with the experimental results of Helminger and De Lucia. Air-broadened linewidths of H₂S at 200°K have also been calculated, so that the temperature dependence can be estimated.     

Far infrared optical excitation in metallic uranium sulfide

Previous near normal incidence reflectivity measurements on US single crystals from 12 to 0.03 eV have been extended down to 0.0018 eV (15 cm^?1). A broad plateau with a reflectivity of 90±2% is observed between 40 and 400 cm^?1 with a further increase of the reflectivity below 40 cm^?1. A Kramers-Kronig transformation of the data shows the existence of a resonance at 315 cm^?1. From a comparison with recent neutron data and other arguments we deduce that this resonance is due to the excitation of a transverse optical phonon coupled to an f→d or d→f interband transition.     

Pressure broadening of hydrogen sulfide

Microwave measurements of the self-broadening parameters of four pure rotational transitions of H₂S have been carried out in the millimeter and submillimeter wavelength region. The resulting parameters are (in MHz torr^-1): 1_1.0?1_0.1, 7.18±0.5; 2_2.0?2_1.1, 6.78±0.5; 2_1.1?2_0.2, 9.10±0.5; 3_3.0?3_2.1, 7.76 ±0.5. In addition. Anderson theory calculations have been carried out for these transitions and are found to be in good agreement.     

Light conduction of metallic two-walled carbon nanotubes

The properties of surface plasmon–polariton modes in metallic two-walled carbon nanotubes are studied, taking into account the retardation effects. The dispersion relation of surface waves is obtained, by solving Maxwell and hydrodynamic equations with appropriate boundary conditions. Numerical results show that the difference between plasmon and plasmon–polariton modes is strongly dependent on the inner-outer radii of the system but only in the long-wavelength cases.     

Density quantization of metallic hydrogen

A cellular model of atomic hydrogen is hypothesized in which the Fermi pressure due to a single foreign electron invading the cell is examined in lieu of the entire degenerate gas. The Schrödinger equation is then solved in a self-consistent fashion with Laplace's equation for the electronic cloud. The Wronskian of the two possible wave functions does not vanish because the homogeneous Neumann condition is applied to the surface of the cell, while the Coulomb singularity compels a solution to be generated from the origin. Two quantum numbers result, one for the energy and one for the density, thus there is a lower limit to the density at zero temperature. Further corrections for electron waves by the Born Von-Karmen conditions broadens the radial quantum number into a continuum, but with an absolute lower limit to the density given by the ground state solutions to the Schrödinger equation.We obtain a bulk modulus of compressibility for metallic hydrogen of about 4.66×10¹² dynes/g on the average over a pressure range of 1 to 25 megabars with a density range of 0.4 to 4 g/cc. This is about a factor of 2 greater than Wigner and Huntington's estimate (1935). The zero temperature pressure and density at a maximum is 20.05 Mb and 4.8 g/cc. At the density Wigner and Huntington propose (0.8 g/cc) for the metallic modification, we obtain a necessary pressure of 2.2 Mb. Wigner and Huntington suggest 0.25 Mb while Stewart's data (1956) suggest about 1 Mb. Recent investigations in the literature run the gamut from 1 to 20 Mb (Alder & Christian, 1960). Furthermore, we obtain a latent heat of fusion of 134.3 kcal/g at maximum density, which decreases to zero at 19.1 Mb. The result means that the metallic state of hydrogen exists only over a pressure range of 1 Mb and below 19 Mb, it is a viscoelastic fluid until the molecular solid, formed above 20 Mb begins to form a plasma.     

Small-polaron versus band conduction in some transition-metal oxides

In this paper an attempt is made to establish the nature of free charge carriers and of charge carriers bound to centres in p-type NiO, CoO and MnO and in n-type MnO and α-Fe₂O₃.

For free charge carriers, d.c. conductivity, Seebeck coefficient and Hall effect are considered. Effects arising from inhomogeneous conduction and impurity conduction are discussed. Impurity conduction appears to have a strong influence on transport properties in the case of α-Fe₂O₃, less so in NiO, whereas no influence of this effect has been found in CoO and MnO. It is shown that NiO and CoO do not exhibit the features characteristic of small-polaron conductors but rather can be consistently conceived of as large-polaron band semiconductors. It is suggested that magnetic resistance due to exchange coupling between charge-carrier spin and cation spins plays an important role. The anomalous behaviour of the Hall effect in NiO and α-Fe₂O₃ is extensively discussed. In contradistinction to NiO, CoO and n-type MnO, free charge carriers in p-type MnO seem to have small-polaron character.

For charge carriers bound to centres, dielectric loss, high-frequency conduction and optical absorption are considered. The dielectric loss data relate to Li or Na centres in NiO, CoO and MnO and to Ti, Zr, Sn, Ta, Nb and presumably oxygen vacancy centres in α-Fe₂O₃. It is concluded from the dependence of dielectric loss on frequency and temperature that bound charge carriers are small polarons. It is shown for the cases of NiO and α-Fe₂O₃ that apart from small-polaron effects, disorder due to locally varying electric fields determines the nature of dielectric loss. The small-polaron character of bound charge carriers in NiO is corroborated by the behaviour of high-frequency conduction and optical absorption due to centres and also by the magnitude of impurity conduction.     

Non-Abrikosov vortices in liquid metallic hydrogen

We consider non-Abrikosov vortex solutions in liquid metallic hydrogen (LMH) in the framework of two-component Ginzburg–Landau model. We have shown that there are three types of non-Abrikosov vortices depending on chosen boundary conditions at the core of vortices, namely, Neumann (N)-type, Dirichlet (D)-type and Gross–Pitaevskii (GP)-type vortices. The Neumann-type vortex has a non-vanishing condensation at the core, that is different from the ordinary vortex, and the magnetic flux could be reversed as well in LMH. Furthermore, we have obtained a new type of a neutral vortex which has no magnetic field. The presence of such a vortex is related to metallic superfluid state suggested by Babaev (2004) [1].     

Magnetophonon oscilation of thermoelectric power in the conduction band of tellurium

At about 200K where the Hall coefficient of p-Te reverses its sign, magnetophonon oscillation of electron in the conduction band was observed for the first time in H6c and H⊥c. It was attained by measuring the second derivative of the longitudinal magneto-Seebeck coefficient (?²α₆/?H²). It is found to be explained fairly well by a simple parabolic band model even for H6c. Effective mass values of the conduction band at 200K are deduced on an interpretation; $\text{m}{}^1{}_{\mathrm{\perp }}\text{=0.160m}{}_0$ and $\text{m}{}^1{}_6\text{= 0.072m}{}_0$. Rather large contribution of electron in ?²α₆/?H² may be due to the enhanced electron diffusion in a transition region from p-type to intrinsic as reported recently in p-InSb. This interpretation is supported also by the oscillation of longitudinal magnetoresistance (?²?₆/?H²) which was observed for H6c.