Modern Physics Letters B

Recently, the measurement of the polar Kerr effect (PKE) in the quasi two-dimensional superconductor Sr₂RuO₄, which is motivated to observe the chirality of p_x + ip_y-wave pairing, has been reported. We clarify that the PKE has intrinsic and extrinsic (disorder-induced) origins. The extrinsic contribution would be dominant in the PKE experiment.

CdTe-doped SiO₂ thin films were produced by RF magnetron co-sputtering technique. Presence of CdTe nanocrystals inside the silica matrix was confirmed by Raman spectroscopy and grazing incidence X-ray diffraction. The samples demonstrate size dependent photoluminescence. Temperature dependent photoluminescence measurements were carried out in the temperature range 15–295 K and revealed energy-emission thermal stability. This feature can be usefully applied in a production of light-emitting diodes with wavelength stability in a wide temperature range.

Within the kinetic energy driven superconducting mechanism, the doping and temperature dependence of the superfluid density in cuprate superconductors is studied throughout the superconducting dome. It is shown that the superfluid density shows a crossover from the linear temperature dependence at low temperatures to a nonlinear one in the extremely low temperatures. In analogy to the dome-like shape of the doping dependent superconducting transition temperature, the maximal zero-temperature superfluid density occurs around the critical doping δ ≈ 0.195, and then decreases in both lower doped and higher doped regimes.

The LaCoO₃ single crystal, 4 mm in diameter and 30 mm in length, has been grown by optical floating zone method. The magnetic measurements show that the coercivity and the remanence are 5 Oe and 1.5 × 10^-3 emu/g at 5 K, respectively. The ZFC and FC magnetic susceptibility curves overlap and the 1/χ(T) curve shows a linear variation over the interval 5 K < T < 35 K in 1000 Oe. As the temperature increases from 35 K to 90 K, the ZFC curve in 1000 Oe firstly reduces nonlinearly, and then appears as a wave crest. The χ under ZFC is higher than that under FC in the temperature range of 55~90 K. In 50 000 Oe, a slope change of 1/χ(T) at about 12 K is observed.

The new scheme of crystalline undulator based on coherent bremsstrahlung from above barrier relativistic electrons interacting with a system of atomic strings periodically deformed by acoustic wave is proposed and studied in the work. The possibility to generate X-rays in the range of about 10 keV and more by electrons with energies of about 100 MeV is shown. Spectral-angular density of the emission being considered may be six times greater than ordinary CB.

For the purpose of multi-layer chip electromagnetic interference (EMI) filters, a series of xTiO₂ + (1 - x)Ni_0.2Cu_0.2Zn_0.62O(Fe₂O₃)_0.98 (NiCuZn ferrite) (0 ≤ x ≤ 60 wt.%) composite ceramics were primarily prepared by a solid-state reaction method. With addition of 3 wt.% Bi₂O₃, all the ceramics can be sintered at 900°C. The effects of composition x on the sintering behaviors, phase compositions and electromagnetic properties of TiO₂+NiCuZn ferrite ceramics were investigated. The X-ray diffraction (XRD) results showed that the ceramics were composed of NiCuZn, Fe₃Ti₃O₁₀ and TiO₂ phases. Scanning electron micrographs showed that 10 wt.% TiO₂ to 90 wt.% Ni_0.2Cu_0.2Zn_0.62O(Fe₂O₃)_0.98 ceramics had small grain size and high density. With an increase of TiO₂ content x, the value of ε_r decreased and the component with 10 wt.% TiO₂ had maximum relative dielectric constant. The permeability and the saturation magnetization decreased gradually with increasing TiO₂ content, and the permeability curve exhibited excellent stability of frequency. The composite materials with 10 wt.% TiO₂ showed typical magnetic hysteresis of the magnetic materials. For the specimens with 10 wt.% TiO₂ to 90 wt.% Ni_0.2Cu_0.2Zn_0.62O(Fe₂O₃)_0.98, the good dielectric (ε_r = 50) and magnetic properties (μ = 30, tanδ|_{10 MHz} = 0.13) have been obtained at 900°C.

A microscopic theoretical study of external magnetic field effect on superconductivity and density of states (DOS) in rare earth nickel borocarbide superconductors (RNi₂B₂C) is reported here. A Hamiltonian model is used to describe the system to which a BCS-type Cooper pairing mechanism is added. The expression for SC order parameter (z) is calculated by the Green's function technique of D. N. Zubarev. The variation of superconducting gap with temperature is investigated at different external magnetic fields. The phase diagram between temperature (θ) and critical magnetic field (b_c) agrees with experimental observations. The gap edges in the DOS appear at ±2z in the absence of external magnetic field. On the application of external magnetic field in the DOS, the gap edges appear at ±(z - b) which resembles the tunneling conductance of STM experiment.

The application of thermal annealing at various annealing temperatures (473–1073 K) has been shown to significantly modify surface morphology of platinum (Pt) metal contacts on AlGaN/GaN/AlN heterostructure grown on silicon by plasma-assisted molecular beam epitaxy (PA-MBE). Structural analysis of the AlGaN/GaN samples used for the Pt Schottky contacts fabrication were performed by using high resolution X-ray diffraction (HR-XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The Pt metal contacts were then deposited on the samples followed by current–voltage (I–V) characterization. Thermally-treated samples showed significant decrease in current compared with untreated samples. From the I–V measurements, the Schottky barrier height (SBH) and ideality factor (n) were calculated. We found that the lowest value of SBH obtained was 0.526 eV at 873 K annealing temperature. Unfortunately, there are no values for the SBH and ideality factor at 1073 K annealing temperature. The SEM analysis has shown some island formation at high annealing temperature due to the difference of surface energies between thin metal films and AlGaN that causes dewetting. We suggest that the reason for the barrier height reduction is due to the metal island formation on the samples.