Effect of the atomic composition of the surface on the electron surface states in topological insulators A<Stack><Subscript>2</Subscript><Superscript>V</Superscript></Stack>B<Stack><Subscript>3</Subscript><Superscript>VI</Superscript></Stack>

The results of the theoretical investigation of the surface electronic structure of A₂^VB₃^VI compounds containing topologically protected surface states are reported. The ideal Bi₂Te₃, Bi₂Se₃, and Sb₂Te₃ surfaces and surfaces with an absent external layer of chalcogen atoms, which were observed experimentally as monolayer terraces, have been considered. It has been shown that the discrepancy between the calculated Fermi level and the value measured in the photoemission experiments can be attributed to the presence of the “dangling bond” states on the surface of the terraces formed by semimetal atoms. The fraction of such terraces on the surface has been estimated.     

Factors affecting the superconductivity in the process of depositing Nd1.85Ce0.15CuO4-δ by the pulsed electron deposition technique

On SrTiO₃ single crystal substrate, by using the pulsed electron deposition technique, the high-quality electron doped Nd_1.85Ce_0.15CuO_4−δ superconducting film was successfully fabricated. After careful study on the R-T curves of the obtained samples deposited with different substrate temperatures, thicknesses, annealing methods and pulse frequencies, the effects of them on the superconductivity of the films were found, and the reasons were also analyzed. Additionally, by using the same model of the pulsed laser deposition technique, the relation between the target-to-substrate distance and the deposition pressure was drawn out as a quantitative one. Supported by the Key Project of Zhejiang Provincial Natural Science Foundation (Grant No. Z605131), the ‘100 Talents Project’ of Chinese Academy of Sciences, the Creative Research Group of National Natural Science Foundation of China (Grant No. 60321001) and the National Natural Science Foundation of China (Grant No. 60571029)     

On the nature of the KH<Subscript>2</Subscript>PO<Subscript>4</Subscript> high-temperature transformation

For over two decades, the high-temperature phase transition (HTPT) at around T _p = 180 °C on KH₂PO₄ (KDP), which involves an ionic conductivity increase, constitutes a controversial subject; while most authors ratify a physical transformation (tetragonal → monoclinic phase transition), others defend the chemical transformation. A careful high-temperature phase behavior examination of this acid salt by means of modulated and conventional differential scanning calorimetry, thermogravimetric analysis, simultaneous thermogravimetric and differential scanning calorimetry, impedance spectroscopy, and temperature evolution of X-ray diffraction was performed to provide a possible solution to this long-standing issue. We found that the structural phase transition does not take place. Instead, a chemical transformation occurs at T _p. When KDP is heated through this temperature, the sample initially corresponding to a single phase (tetragonal) transforms to a sample composed of two solid phases: tetragonal KDP, located at its bulk, and monoclinic potassium metaphosphate (KPO₃), located at its surface. Most of the water produced evaporates, but a small portion of liquid water bonds to KPO₃. Because this is of polymeric nature, it takes the role of a host matrix that contains liquid water regions. Consequently, given that part of the water dissolves a portion of surface salt (providing protons), the surface sample system behaves in a similar manner to a polymer electrolyte membrane where the proton transport mechanism includes the vehicle type, using hydronium (H₃O⁺) as a charge carrier. On further heating, the bulk tetragonal KDP phase reduced to its total decomposition. The metastability of the high-temperature phase below T _p is also explained.     

Influence of the special features of the effective magnetic anisotropy on the temperature dependences of the magnetoimpedance of nanocrystalline Fe<Subscript>73.5</Subscript>Si<Subscript>16.5</Subscript>B<Subscript>6</Subscript>Nb<Subscript>3</Subscript>Cu<Subscript>1</Subscript> strips

The influence of the thermal treatment type on the temperature dependences of the magnetoimpedance of nanocrystalline Fe_73.5Si_16.5B₆Nb₃Cu₁ alloy strips is investigated. The main mechanisms determining the temperature behavior of the magnetoimpedance of strips with induced magnetic anisotropy having various special features are established. The prospects for application of the alloy strips nanocrystallized in the presence of a magnetic field as sensitive elements of temperature sensors and special magnetic field detectors are demonstrated.     

Energy spectrum of the low-lying states in Sr<Subscript>2</Subscript>FeSi<Subscript>2</Subscript>O<Subscript>7</Subscript> and the nature of the magnetoelectric effect

A mechanism underlying the magnetoelectric effect is discussed. This mechanism is related to the combined action of an odd crystal field, spin?orbit coupling, and the interaction of the orbital angular momentum with an applied magnetic field. The effective operator describing the spin states of Fe²⁺ ions is obtained. Such operator allows one to interpret the terahertz spectroscopy data and to calculate both the electric field effect on the magnetization and the magnetic field effect on the electric polarization of the sample. It is demonstrated that the magnetoelectric effect is enhanced with a decrease in the energy corresponding to the tetragonal distortion of ligand tetrahedra.     

Magneto-optical investigations of the domain structure and magnetization of the ferrite-garnet Tb<Subscript>0.2</Subscript>Y<Subscript>2.8</Subscript>Fe<Subscript>5</Subscript>O<Subscript>12</Subscript> in the temperature range of the spontaneous spin-reorientation phase transition

The transformation of a domain structure and technical magnetization of the Tb_0.2Y_2.8Fe₅O₁₂ single crystal in the temperature range of the spontaneous orientational phase transition have been investigated by the magneto-optical method. It has been shown that the phase transition is extended in a certain temperature range in which domains of the low-temperature and high-temperature magnetic phases coexist. It has been found that the evolution of the domain configuration in the temperature range of spin reorientation substantially depends on the presence of mechanical stresses in the crystal. Anomalies in the temperature dependences of the coercivity and magneto-optical susceptibility of the crystal due to the transformation of its domain structure during the phase transition have been revealed. The experimental results have been interpreted within the existing theory of orientational phase transitions in cubic crystals.     

On the interpretation of the phase diagram of La<Subscript>2−x</Subscript>M<Subscript>x</Subscript>CuO<Subscript>4</Subscript>

The difference between the phase diagrams of La_2?x(Ba,Sr)_xCuO₄ and Nd_2?xCe_xCuO₄ is discussed. It is proposed that the discrepancy of x-values corresponding to the transition from antiferromagnetic dielectric state to conducting one (respectively, x≈0.06 in La_2?x(Ba,Sr)_xCuO₄ and x≈0.125 in Nd_2?xCe_xCuO₄) results from non-homogeneous doping of La_2?x(Ba,Sr)_xCuO₄ over the range 0.06<x<0.125, when localized holes are added to each second CuO₂ layer. Therefore the actual phase diagram of the “holedoped” superconductor La_2?x(Ba,Sr)_xCuO₄ coincides with one for the “electron-doped” superconductor Nd_2?xCe_xCuO₄. It is shown that all features observed in La_2?x(Ba,Sr)_xCuO₄ around x=0.125 are clarified on this basis.     

Study of the formation and stability of the NdSr<Subscript>2</Subscript>Mn<Subscript>2</Subscript>O<Subscript>7</Subscript> phase

The sequence of phase equilibria during synthesis of the NdSr₂Mn₂O₇ phase is determined. The stability of this phase with changes in temperature and partial oxygen pressure is investigated.     

Testing the minimal supersymmetric standard model with the mass of the <Emphasis Type="Italic">W</Emphasis> boson

We review the currently most accurate evaluation of the W boson mass, M _W , in the minimal supersymmetric standard model (MSSM). It consists of a full one-loop calculation, including the complex phase dependence, all available MSSM two-loop corrections as well as the full standard model result. We analyse the impact of the phases in the scalar quark sector on M _W and compare the prediction for M _W based on all known higher-order contributions with the experimental results.      

Investigation of low-lying levels of the <Stack><Subscript>4</Subscript><Superscript>8</Superscript></Stack>Be nucleus in the multiquantum approximation of the orthogonal scheme

In the multiquantum approximation of the orthogonal scheme, specific calculations for the energies and radii of the ₄ ⁸ Be nucleus are performed with allowance for all states characterized by the λ=[44] Young diagram, the quantum numbers K_min and K_min+2 of the O(3(A?1)) group, and the quantum numbers E=K+2N (N≤9) of the U(3(A?1)) group. The convergence of the results with respect to the extension of the basis is studied, and the structure of relevant wave functions is revealed. The results of these calculations are compared with the results obtained in the analogous approximation of the unitary scheme.     

Re-evaluation of the LHC potential for the measurement of <Emphasis Type="Italic">m</Emphasis><Subscript><Emphasis Type="Italic">W</Emphasis></Subscript>

We present a study of the LHC sensitivity to the W boson mass based on simulation studies. We find that both experimental and phenomenological sources of systematic uncertainties can be strongly constrained with Z measurements: the lineshape, dσ _Z /dm, is robustly predicted, and its analysis provides an accurate measurement of the detector resolution and absolute scale, while the differential cross-section analysis, d² σ _Z /dydp _T , absorbs the strong interaction uncertainties. A sensitivity δ m _W ∼7 MeV for each decay channel (W→e ν, W→μ ν), and for an integrated luminosity of 10 fb⁻¹, appears as a reasonable goal.     

The dependence of the Fe <Emphasis Type="Italic">K</Emphasis><Subscript><Emphasis Type="BoldItalic">α</Emphasis></Subscript> yield on the chirp of the femtosecond exciting laser pulse

The hard X-ray yield generated with femtosecond laser pulses is studied for differently chirped irradiating laser pulses. The radiation of a Ti:sapphire CPA laser system (29 fs, 750 μJ, 1 kHz) is focused onto an iron containing solid state target producing incoherent hard X-ray radiation, Bremsstrahlung as well as target-specific K_α and K_β lines. The hard X-ray yield has been optimized by introducing negative and positive group delay dispersion (GDD) and third order dispersion (TOD) to the femtosecond laser pulse. The K_α yield could be enhanced by a factor of 1.7 and reached 1.9×10⁸ Fe K_α photons/s in 4π with the laser pulse positively chirped, and 1.5×10⁸ Fe K_α photons/s with the pulse negatively chirped. When the pulse energy is lowered to about 400 μJ the yield maximum at negative chirp vanishes and only the maximum at positive chirp remains. We explain this behavior with an increased electron temperature caused by the induced GDD and TOD in the pulse. PACS 42.65.Re; 52.38.Ph; 52.50.Jm     

Phase separation of the spin system in the La<Subscript>0.93</Subscript>Sr<Subscript>0.07</Subscript>MnO<Subscript>3</Subscript> crystal

The magnetic state of the manganite La_0.93Sr_0.07MnO₃ in the range 4.2–290 K was studied using elastic neutron scattering. The magnetic state of this compound was found to occupy a particular place in the La_1?xSr_xMnO₃ solid-solution system, in which the antiferromagnetic type of order (LaMnO₃, T_N=139.5 K) switches to ferromagnetic ordering (La_0.9Sr_0.1MnO₃, T_C=152 K) with increasing x. In the transition state, this compound contains large-scale spin configurations of two types. A fractional crystal volume of about 10% is occupied by regions of the ferromagnetic phase with an average linear size of 200 Å, while the remainder of the crystal is a phase with a nonuniform canted magnetic structure. Arguments are presented for the phase separation of the La_0.93Sr_0.07MnO₃ spin system being accounted for by Mn⁴⁺ ion ordering.     

Critical behavior of the heat capacity of the manganite La<Subscript>0.87</Subscript>K<Subscript>0.13</Subscript>MnO<Subscript>3</Subscript>

The heat capacity of the manganite La_0.87K_0.13MnO₃ has been measured in the temperature range 80–350 K. The nature of the ferromagnetic phase transition and the critical properties of heat capacity near the Curie temperature have been studied. The regularities of variations in the universal critical parameters near the phase transition point have been established. The calculated critical exponent and amplitudes of the heat capacity with allowance for corrections on the scaling (α = −0.13 and A ⁺/A ⁻ = 1.178) correspond to the critical behavior of the 3D Heizenberg model.     

Heat capacity of the La<Subscript>0.9</Subscript>Ag<Subscript>0.1</Subscript>MnO<Subscript>3</Subscript> manganite near the curie temperature

The heat capacity of the La_0.9Ag_0.1MnO₃ manganite is measured in the temperature range 77–350 K and studied in detail in the vicinity of the Curie temperature for the first time. The regularities of the variation in the universal critical parameters in the vicinity of the phase transition point are established. The critical exponent and the amplitude of the heat capacity are calculated to be α = ?0.127 and A ⁺/A ^? = 1.146 with due regard for the scaling corrections. These parameters correspond to the critical behavior within the three-dimensional Heisenberg model. The size of ferromagnetic droplets in the paramagnetic range at T > T _C is estimated as ξ ≈ 19 Å. The results obtained are analyzed thoroughly and compared with theoretical data for a number of model systems.