Metallic layer in the Earth’s lower mantle

We predict the insulator-metal-insulator transitions for the temperature and pressure of the lower mantle with the metal layer thickness Δh ≈ 400 km at the depth of 1400–1800 km. The insulator-metal transition has the Mott-Hubbard origin, while the second transition from metal to insulator results from spin crossover of the Fe²⁺ ions from high spin S = 2 to low spin S = 0 state. The conductivity in the metal layer may attain 250 S/m. The depth profile of the conductivity is also suggested.     

Effect of spin crossovers on the Mott-Hubbard transition at high pressures

The effect of spin crossovers in d _n terms on the effective Hubbard parameter (U _eff) determining the gap between the lower and upper Hubbard bands is analyzed using a many-electron approach to describe the electron structure of Mott insulators. A new mechanism of the insulator-metal transition is established for d ⁵ ions, which is related to a decrease in U _eff caused by spin crossover. For other ions, the U _eff value is either independent of pressure (d ², d ⁴, d ⁷) or it exhibits nonmonotonic growth (d ³, d ⁶, d ⁸).     

Optical Hall conductivity of systems with gapped spectral nodes

We calculate the optical Hall conductivity within the Kubo formalism for systems with gapped spectral nodes, where the latter have a power-law dispersion with exponent n. The optical conductivity is proportional to n and there is a characteristic logarithmic singularity as the frequency approaches the gap energy. The optical Hall conductivity is almost unaffected by thermal fluctuations and disorder for n = 1, whereas disorder has a stronger effect on transport properties if n = 2.     

ESR-Linienbreite der Ionen der Eisengruppe in Lösungen

Electron spin resonance linewidths of ions belonging to the first transition group with quenched orbital angular momentum are calculated using a modified relaxationmatrix theory including third and fourth order perturbation terms. We base our calculation on a Hamiltonian, which depends on electron spin, nuclear spin, orbital angular momentum, rotation of the whole complex, and vibration of the ligands. Quadrupol effects, intermolecular electron-electron and electron-nucleus interactions are neglected. The results show that the well-known formula of the transverse relaxation time derived by using the spin-Hamiltonian is correct, if first the contribution of the rotational spin orbit process is taken in consideration and second the rotational correlation timeτ _c is replaced byτ _v =(1/τ _c +1/τ(0))^?1. 1/τ(0) describes the linewidth of the lowest energy value of the electrostatic energy of unpaired electrons in the ligand field. The linewidth arises from the normal modes of the complex; the calculation gives τ(0)=l0^?11...10^?12 sec.     

Conductivity and anomalous Hall effect in film magnetic nanocomposites based on nonstoichiometric oxides

The transport properties of film nanocomposites (Co₄₀Fe₄₀B₂₀) _x (AlO _y )_{100 ? x} and (Co₈₄Nb₁₄Ta₂) _x (AlO _y )_{100 ? x} based on AlO _y oxide (y ~ 1), containing a ferromagnetic metal, are studied in the region of the metal–insulator transition (57 > x > 47 at %). It is found that at x > 49 at %, the conductivity of nanocomposites is well described by a logarithmic law of σ(T) = a + b ln T, which can be explained by the peculiarities of the Coulomb interaction in nanogranular systems with metallic conductivity near the metal—insulator transition. It is shown that parameter b is determined by the characteristic size of the percolation cluster cell, which in nanocomposites of both types happen to be the same (~8 nm) and correlates well with the results of electron microscopy studies. The temperature dependence of the anomalous Hall effect at the logarithmic dependence of conductivity is studied for the first time. In the immediate vicinity of the transition, a power-law scaling between the anomalous Hall resistance and longitudinal resistance ρ _H ^a ∝ ρ^0.4, is detected, which can be explained by the suppression of its own mechanism of the anomalous Hall effect under the strong scattering of charge carriers.     

Superconductor-insulator transition tuned by annealing in Bi-film on top of Co-clusters

We deposited amorphous Bi films with a thickness between 3 and 6.5 nm at 4.2 K on top of previously deposited Co clusters having a mean size of ～4.5 nm. The Co cluster layers thickness was between 2.3 and 5 nm. In-situ electrical transport measurements were performed between 2 and 100 K. Measurements on as-prepared samples having a Bi layer thickness of 3.0 nm show hopping (tunneling) conductivity as σ(T) = σ ₀ exp[?(T ₀/T)^1/2] above the superconducting transition temperature T _C and re-entrance behavior again with hopping (tunneling) conductivity below T _C . Annealing of films having a Bi layer thickness of 5.5 nm results in a decrease of resistivity, with variable-range hopping conduction behavior as σ(T) = σ ₀ exp[?(T ₀/T)^1/3 ]. Quite different are the findings for films having a Bi layer thickness of 6.5 nm: annealing of these films results in a power-law behavior as σ(T) = σ ₀ T ^α with α = 2/3, indicating that these films are close to a quantum critical point separating superconducting and insulating phases. A phase diagram including all experimental observations is proposed.     

Pseudogap and its temperature dependence in YBCO from the data of resistance measurements

The temperature dependence of the excess conductivity Δσ for Δσ = A(1 ? T/T^*)exp(Δ^*/T) (YBCO) epitaxial films is analyzed. The excess conductivity is determined from the difference between the normal resistance extrapolated to the low-temperature range and the measured resistance. It is demonstrated that the temperature dependence of the excess conductivity is adequately described by the relationship Δσ = A(1 ? T/T^*)exp(Δ^*/T). The pseudogap width and its temperature dependence are calculated under the assumption that the temperature behavior of the excess conductivity is associated with the formation of the pseudogap at temperatures well above the critical temperature T _c of superconductivity. The results obtained are compared with the available experimental and theoretical data. The crossover to fluctuation conductivity near the critical temperature T _c is discussed.     

Numerical analysis of electronic conductivity in graphene with resonant adsorbates: comparison of monolayer and Bernal bilayer

We describe the electronic conductivity, as a function of the Fermi energy, in the Bernal bilayer graphene (BLG) in presence of a random distribution of vacancies that simulate resonant adsorbates. We compare it to monolayer (MLG) with the same defect concentrations. These transport properties are related to the values of fundamental length scales such as the elastic mean free path L _e , the localization length ξ and the inelastic mean free path L _i . Usually the later, which reflect the effect of inelastic scattering by phonons, strongly depends on temperature T. In BLG an additional characteristic distance l ₁ exists which is the typical traveling distance between two interlayer hopping events. We find that when the concentration of defects is smaller than 1%–2%, one has l ₁ ≤ L _e ? ξ and the BLG has transport properties that differ from those of the MLG independently of L _i (T). Whereas for larger concentration of defects L _e <l ₁ ? ξ, and depending on L _i (T), the transport in the BLG can be equivalent (or not) to that of two decoupled MLG. We compare two tight-binding model Hamiltonians with and without hopping beyond the nearest neighbors.     

<Superscript>14</Superscript>N Nuclear Magnetic Resonance and Relaxation in the Paramagnetic Region of Uranium Mononitride

The spin susceptibility of a polycrystalline sample of uranium mononitride UN is studied by measuring the ¹⁴N NMR line shift, spin–lattice relaxation rates of the nuclear spin, and static magnetic susceptibility in the temperature region of 1.5T_N < T < 7T_N A joint analysis of the results obtained has revealed the temperature dependence of the characteristic energy of spin fluctuations of the uranium 5f electrons: Γ_nmr(T) ∝ T^0.54(4) close to the dependence Γ(T) ∝ T^0.5 characteristic of concentrated Kondo systems above the coherent state formation temperature.     

Single and double spin asymmetries in the elastic <Emphasis Type="Italic">e</Emphasis>-<Emphasis Type="Italic">d</Emphasis> scattering and their dependence on the deuteron wave function

Single and double spin asymmetries in the elastic electron-deuteron (e-d ) scattering were investigated. The tensor-deuteron asymmetries T_2i(i = 0, 1, 2) and the beam-vector-deuteron asymmetries T ^e _1i(i = 0, 1) were calculated and compared with the available experimental data. The sensitivity of the results for these spin asymmetries to the deuteron wave function has been investigated. The predicted asymmetries were found to be agree with one another and with experiment. It was found that, the double spin asymmetry T ^e ₁₀ is much smaller than the T ^e ₁₁-asymmetry. Therefore, in addition to the single tensor-deuteron asymmetry T₂₀, the doubly beam-vector-deuteron asymmetry T ^e ₁₁ can be used as an another tool for extracting the deuteron electromagnetic form factors.     

Nuclear magnetic relaxation of spin<Emphasis Type="Italic">I</Emphasis>=1/2 scalar coupled to a quadrupolar nucleus in the presence of cross-correlation effects

The rigorous treatment of relaxation for the dipolar-multipolarAX spin system (I=1/2,S>1/2) in the presence of the dipolarI-S coupling, anisotropy chemical shift and quadrupolar interaction ofS spin is proposed. The calculations of the spin evolution under the relaxation Hamiltonian are based on the second-order time-dependent perturbation theory and are carried out in the operator representation. For this task the double commutator identities of the type [[I _±S _z ⁿ ,A _q ^μp ]A _?q ^μp ] and [[I _zS _z ⁿ ,A _q ^μp ]A _?q ^μp. ] are derived. The fist-order differential equations for the evolution of longitudinal two-spin orderI _zS _z ⁿ , z=magnetization ofS spinS _z ⁿ and coherences <I _±S _z ⁿ > in the spin systemIS with scalar coupling between spin 1/2 and quadrupolar spinS>1/2 were obtained. These equations are used to get equations for the evolutions of each component of the multiplet structure of spinI. The imaginary part of the cross-correlation spectral density function and indirect spin-spin coupling Hamiltonian are taken into account. Equations for the longitudinal components of theI spin spectrum in the presence of cross-correlation effects were obtained also. Longitudinal and transverse relaxation times and cross-relaxation times in the presence of cross-correlation D-CSA, Q-CSA, Q-D were analyzed.     

Elastic Deuteron Scattering on the <Superscript>12</Superscript>C Nucleus within a Three-Body Model

The formalism developed earlier for elastic pd scattering on the basis of Glauber theory with allowance for a total spin dependence is modified by replacing pN amplitudes by amplitudes for N¹²C scattering and is applied to elastic deuteron scattering on the ¹²C nucleus. The amplitudes for elastic N¹²C scattering are obtained within the optical model. Respective numerical calculations performed at the kinetic deuteron-beam energy of 270 MeV lead to results that agree well with data on the differential cross section for d¹²C scattering into the forward hemisphere, but the calculated spin observable A _y ^d agrees with experimental data only qualitatively.     

A theoretical investigation of structural,mechanical, electronic and thermoelectric properties of orthorhombic CH<Subscript>3</Subscript>NH<Subscript>3</Subscript>PbI<Subscript>3</Subscript>

The structural, mechanical, electronic and thermoelectric properties of the low temperature orthorhombic perovskite phase of CH₃NH₃PbI₃ have been investigated using density functional theory (DFT). Elastic parameters bulk modulus B, Young’s modulus E, shear modulus G, Poisson’s ratio ν and anisotropy value A have been calculated by the Voigt–Reuss–Hill averaging scheme. Phonon dispersions of the structure were investigated using a finite displacement method. The relaxed system is dynamically stable, and the equilibrium elastic constants satisfy all the mechanical stability criteria for orthorhombic crystals, showing stability against the influence of external forces. The lattice thermal conductivity was calculated within the single-mode relaxation-time approximation of the Boltzmann equation from first-principles anharmonic lattice dynamics calculations. Our results show that lattice thermal conductivity is anisotropic, and the corresponding lattice thermal conductivity at 150 K was found to be 0.189, 0.138, and 0.530 Wm^?1K^?1 in the a, b, and c directions. Electronic structure calculations demonstrate that this compound has a DFT direct band gap at the gamma point of about 1.57 eV. The electronic transport properties have been calculated by solving the semiclassical Boltzmann transport equation on top of DFT calculations, within the constant relaxation time approximation. The Seebeck coefficient S is almost constant from 50 to 150 K. At temperatures 100 and 150 K, the maximal figure of merit is found to be 0.06 and 0.122 in the direction of the c-axis, respectively.     

Electronic transport through a Majorana bound state coupled to a T-shaped quantum-dot system with Coulomb interaction

Using the Green’s function technique, we respectively investigate the electron transport properties of two spin components through the system of a T-shaped double quantum dot structure coupled to a Majorana bound state, in which only one quantum dot is connected with two metallic leads. We explore the interplay between the Fano effect and the MBSs for different dot-MBS coupling strength λ, dot-dot coupling strength t, and MBS-MBS coupling strength ε_M in the noninteracting case. Then the Coulomb interaction and magnetic field effect on the conductance spectra are investigated. Our results indicate that G_↓(ω) is not affected by the Majorana bound states, but a “0.5” conductance signature occurs in the vicinities of Fermi level of G_↑(ω). This robust property persists for a wide range of dot-dot coupling strength and dot-MBS coupling strength, but it can be destroyed by Coulomb interaction in quantum dots. By adjusting the size and direction of magnetic field around the quantum dots, the “0.5” conductance signature damaged by U can be restored. At last, the spin magnetic moments of two dots by applying external magnetic field are also predicted.     

Low-temperature thermal conductivity of tellurium-doped bismuth

Phonon thermal conductivities κ₂₂ (?T ‖ C1) and κ₃₃ (? T ‖ C₃) of tellurium-doped bismuth with an electron concentration in the range 1.8 × 10¹⁹ ≤ n_L ≤ 1.4 × 10²⁰ cm^?3 were studied in the temperature interval 2 < T < 300 K. The temperature dependence of the phonon thermal conductivity obtained on doped bismuth samples of both orientations exhibits two maxima, one at a low temperature and the other at a high temperature. The effect of various phonon relaxation mechanisms on the dependence of both phonon thermal conductivity maxima on temperature, impurity concentration, and electron density is studied.     

Effect of cation substitution in Cs<Subscript>1–2<Emphasis Type="Italic">x</Emphasis></Subscript>Ba<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>H<Subscript>2</Subscript>PO<Subscript>4</Subscript> on structural properties and proton conductivity

We synthesized compounds with partial substitution of Cs⁺ cations in CsH₂PO₄ by Ba²⁺ cations. The structural, electron transport and thermodynamic properties of Cs_1–2x Ba _x H₂PO₄ (x = 0–0.15) were studied for the first time with the help of a set of physicochemical methods: infrared and impedance spectroscopy, X-ray diffraction and synchronous thermal analysis. The proton conductivity of Cs_1–2x Ba _x H₂PO₄ at 50–230°C was investigated in detail by impedance measurements. The formation of solid substitution solutions isostructural with CsH₂PO₄ (P2₁/m) is observed in the range of substitution degrees of x = 0–0.1, with a slight decrease in the unit cell parameters and some salt amorphization. The conductivity of disordered Cs_1–2x Ba _x H₂PO₄ in the low-temperature region increases by two orders of magnitude at x = 0.02 and increases with an increasing fraction of barium cations by three or four orders of magnitude at x = 0.05–0.1; the superionic phase transition practically disappears. At x = 0.15, heterophase systems based on salts are formed, showing high conductivity and a further decrease in the activation energy of conductivity to 0.63 eV. The conductivity of the high-temperature phase of Cs_1–2x Ba _x H₂PO₄ does not change with increasing fraction of the substituent.     

Genesis of the anomalous Hall effect in CeAl<Subscript>2</Subscript>

The Hall coefficient R _H , resistivity ρ, and Seebeck coefficient S of the CeAl₂ compound with fast electron density fluctuations were studied in a wide temperature range (from 1.8 to 300 K). Detailed measurements of the angular dependences R _H (? T, H≤70 kOe) were performed to determine contributions to the anomalous Hall effect and study the behavior of the anomalous magnetic R _H ^am and main R _H ^a components of the Hall signal of this compound with strong electron correlation. The special features of the behavior of the anomalous magnetic component R _H ^am were used to analyze the complex magnetic phase diagram H-T determined by magnetic ordering in the presence of strong spin fluctuations. An analysis of changes in the main contribution R _H ^a (H, T) to the Hall effect made it possible to determine the complex activation behavior of this anomalous component in the CeAl₂ intermetallic compound. The results led us to conclude that taking into account spin-polaron effects was necessary and that the Kondo lattice and skew-scattering models were of very limited applicability as methods for describing the low-temperature transport of charge carriers in cerium-based intermetallic compounds. The effective masses and localization radii of manybody states in the CeAl₂ matrix were estimated to be (55–90)m₀ and 6–10 Å, respectively. The behaviors of the parameters R _H , S, and ρ were jointly analyzed. The results allowed us to consistently describe the transport coefficients of CeAl₂.     

<Emphasis Type="Italic">cis</Emphasis> Versus <Emphasis Type="Italic">trans</Emphasis>-Azobenzene: Precise Determination of NMR Parameters and Analysis of Long-Lived States of <Superscript>15</Superscript>N Spin Pairs

We provide a detailed evaluation of nuclear magnetic resonance (NMR) parameters of the cis- and trans-isomers of azobenzene (AB). For determining the NMR parameters, such as proton–proton and proton–nitrogen J-couplings and chemical shifts, we compared NMR spectra of three different isotopomers of AB: the doubly ¹⁵N labeled azobenzene, ¹⁵N,¹⁵N′-AB, and two partially deuterated AB isotopomers with a single ¹⁵N atom. For the total lineshape analysis of NMR spectra, we used the recently developed ANATOLIA software package. The determined NMR parameters allowed us to optimize experiments for investigating singlet long-lived spin states (LLSs) of ¹⁵N spin pairs and to measure LLS lifetimes in cis-AB and trans-AB. Magnetization-to-singlet-to-magnetization conversion has been performed using the SLIC and APSOC techniques, providing a degree of conversion up to 17 and 24% of the initial magnetization, respectively. Our approach is useful for optimizing the performance of experiments with singlet LLSs; such LLSs can be exploited for preserving spin hyperpolarization, for probing slow molecular dynamics, slow chemical processes and also slow transport processes.     

Room Temperature Spin Accumulation Effect in Boron Doped Si Created by Epitaxial Fe<Subscript>3</Subscript>Si/<Emphasis Type="Italic">p</Emphasis>-Si Schottky Contact

To study spin-dependent transport phenomena in Fe₃Si/p-Si structures we fabricated 3-terminal planar microdevices and metal/semiconductor diode using conventional photolithography and wet chemical etching. I?V curve of prepared diode demonstrates rectifying behavior, which indicates the presence of Schottky barrier in Fe₃Si/p-Si interface. Calculated Schottky barrier height is 0.57 eV, which can provide necessary conditions for spin accumulation in p-Si. Indeed, in 3-terminal planar device with Fe₃Si/p-Si Schottky contact Hanle effect was observed. By the analysis of Hanle curves spin lifetime spin diffusion length in p-Si were calculated, which are 145 ps and 405 nm, respectively (at T = 300 K). Spin lifetime strongly depends on temperature which can be related to the fact that spin-dependent transport in our device is realized via the surface states. This gives a perspective of creation of spintronic devices based on metal/semiconductor structure without need for forming tunnel or Schottky tunnel contact.     

Temperature Dependence of the Thermal Conductivity of a Trapped Dipolar Bose-Condensed Gas

The thermal conductivity of a trapped dipolar Bose condensed gas is calculated as a function of temperature in the framework of linear response theory. The contributions of the interactions between condensed and noncondensed atoms and between noncondensed atoms in the presence of both contact and dipole-dipole interactions are taken into account to the thermal relaxation time, by evaluating the self-energies of the system in the Beliaev approximation. We will show that above the Bose-Einstein condensation temperature (T?>?T _BEC ) in the absence of dipole-dipole interaction, the temperature dependence of the thermal conductivity reduces to that of an ideal Bose gas. In a trapped Bose-condensed gas for temperature interval k _B T?<<?n ₀ g _B , E _p ?<<?k _B T (n ₀ is the condensed density and g _B is the strength of the contact interaction), the relaxation rates due to dipolar and contact interactions between condensed and noncondensed atoms change as \( {\tau}_{dd12}^{-1}\propto {e}^{-E/{k}_BT} \) and τ _c12?∝?T ^?5, respectively, and the contact interaction plays the dominant role in the temperature dependence of the thermal conductivity, which leads to the T ^?3 behavior of the thermal conductivity. In the low-temperature limit, k _B T?<<?n ₀ g _B , E _p ?>>?k _B T, since the relaxation rate \( {\tau}_{c12}^{-1} \) is independent of temperature and the relaxation rate due to dipolar interaction goes to zero exponentially, the T ² temperature behavior for the thermal conductivity comes from the thermal mean velocity of the particles. We will also show that in the high-temperature limit (k _B T?>?n ₀ g _B ) and low momenta, the relaxation rates \( {\tau}_{c12}^{-1} \) and \( {\tau}_{dd12}^{-1} \) change linearly with temperature for both dipolar and contact interactions and the thermal conductivity scales linearly with temperature.