Atomic dynamics of lead embedded into nanoporous glass

The thermal atomic vibration spectrum of lead nanostructured in porous glass with an average pore size of 7 nm and the thermal vibration spectrum of conventional bulk lead (taken for comparison) are measured using inelastic neutron scattering. The density of states in the phonon spectrum of lead nanoparticles is found to exceed the density of states in the spectrum of bulk lead at both low (E < 2.5 meV) and high (E > 9.5 meV) energies. These data are used to propose a model for the structure of a porous glass-lead nano-composite.     

Surface and volume superconductivity of Pb embedded in nanopores

The heat capacity of lead embedded in glass nanopores (7 nm in diameter) and bulk lead was studied in the temperature range 2–40 K without a magnetic field and in magnetic fields of 1–8 T. The properties of lead nanoparticles and bulk lead were compared. The results obtained allowed us to separate the surface superconductivity from the volume superconductivity. The temperature dependence of the heat capacity of lead nanoparticles was shown to exhibit two superconducting transitions above and below the transition temperature for bulk lead (T _c = 7.2 K), which are associated with the surface and volume superconductivity. The upper critical fields H _c3 for the surface superconductivity and H _c2 for the volume superconductivity were determined. It turned out that these fields for Pb nanoparticles are two orders of magnitude higher than those for bulk lead. The “superconductor-normal metal” phase diagrams were constructed for lead nanoparticles. The study established an increase in the density of low-frequency excitations in Pb nanocrystals as compared to bulk Pb and a difference in the electronic heat capacity of Pb nanoparticles as compared to bulk Pb.     

Frequency dependent magnetic susceptibility and spin glass freezing inPtMn alloys

We report measurements of the low-field complex magnetic susceptibility on Pt_1?x Mn _x forx=0.01, 0.025 and 0.05 and for frequencies ν between 10 and 4,000 Hz. A strong frequency dependence of the freezing temperatureT _f is observed: ΔT _f /T _f Δ lnv=0.025 (decade ν)^?1 for all three alloys. These results as well as previous other measurements are interpreted in terms of a phenomenological model.     

Estimates of the s-d interaction in CdCr from superconducting transition temperature and magnetic susceptibility

Cr has a well developed magnetic moment in a Cd host and the superconducting transition temperature, T_c, is strongly depressed. We estimate a spin, S = 1.5 leading to a depression rate - $\text{dT}{}_{\mathrm{c}}\text{dc}\text{= 140 K/at.\%}$. The s-d interaction strength is estimated to 0.5–0.7 eV leading to a Kondo temperature in the milliKelvin range.     

Electron tomography on nanopores embedded in epitaxial GaSb thin films

This work reports on the morphology of nanopores and their spatial position in group III-Sb based multilayer heterostructures grown by molecular beam epitaxy on Si(0 0 1) substrates. By using electron tomography based on dark-field scanning transmission electron microscopy, quantitative information in real space is obtained about individual nanopores unintentionally embedded in GaSb layers. For this purpose adequate needle-shaped samples have to be specifically prepared from the compact material system by focused ion beam. The three-dimensional reconstruction of the probed volume allows the determination of the spatial arrangement of the pores and the analysis of the detailed shape, i.e. the crystallographic facets. Based on these results, the nanopore's geometric shape is discussed with respect to the minimization of surface tension. The formation process can be explained by an agglomeration of vacancies which are generated during the heterostructure growth.     

Phenomenological approach to the non-spin-wave behavior of cuprate magnetic susceptibility in the superconducting state

Experimental data on the non-spin-wave behavior of the cuprate magnetic susceptibility χ(q, ω) in the superconducting state are reconstructed on the basis of a spherically symmetric self-consistent approach within the framework of the frustrated Heisenberg model. For the Green’s function of the spin-wave excitations, a polarization operator resonant with the superconducting state is introduced phenomenologically. This gives rise to an additional (compared to the normal state) branch of the incommensurate peaks and to a pronounced non-spin-wave behavior of the susceptibility χ(q, ω) in the frequency range near 80 meV (the so-called “dark region”). The renormalization of the real part of the polarization operator plays a crucial role in the theory.     

Dual features of magnetic susceptibility in superconducting cuprates: a comparison to inelastic neutron scattering

Starting from the generalized t−J−G model Hamiltonian, we analyze the spin response in the superconducting cuprates taking into account both local and itinerant spin components which are coupled to each other self-consistently. We demonstrate that derived expression reproduces the basic observations of neutron scattering data in YBa₂Cu₃O_6+y compounds near the optimal doping level.     

Properties of superfine superconducting filaments embedded in normal matrix

The size-, surface- and proximity-effects are combined for calculating the critical temperature and some unusual electromagnetic properties of superfine superconducting NbTi filaments (i.e. with a diameterd _s < 0·1 μm) in the neighbourhood of normal metal (Cu). It is shown that the existence of the one-dimensional flux line lattice is responsible for the extremely large values of the critical current densities in low magnetic fields (B < 0·2B _c2,B _c2 — the upper critical magnetic field), for the maximum of the volume pinning force at low magnetic fields (B _m ≈ 0·1B _c2, comparing withB _m≈ 0·5B _c2 in usual macroscopic multifilamentary NbTi superconductors), as well as for the peculiar minimum of the magnetization after reversing the magnetic field direction. The possible role of the frozen-in flux lines in creating flux lines of opposite direction is sketched. It is proposed that for practical purposes the superconducting filaments should be coated with electrically insulating material (e.g. cupro-nickel or dielectric) to destroy the electro-magnetic coupling between the filaments and to ensure low ac losses in the composite.     

Phase transitions in KNO3 embedded in MCM-41 films with regular nanopores

This paper reports on a comparative study of phase transitions in nanocomposites made up of KNO₃ embedded in 10-μm-thick MCM-41 films with unidirectional pores 4.0 nm in size on an aluminum substrate and of nanocomposites prepared in the form of potassium-nitrate-filled pressed MCM-41 powders with 3.7-nm pores. The temperature dependences of linear permittivity and the amplitude of third harmonic generation have been measured under heating and cooling. The structural transition from phase II to phase I shifts under heating relative to that occurring in bulk KNO₃ toward lower temperatures for potassium nitrate in the film and toward higher temperatures for the pressed MCM-41-based nanocomposite. A significant difference has been observed also within the region of existence of ferroelectric phase III. The data obtained suggest that the shifts of phase transition temperatures observed in the conditions of nanoconfinement are influenced markedly not only by pore size and geometry but also by other factors.     

超导磁分离技术的应用研究

首先介绍超导磁分离技术的基本原理、磁选设备的发展概况,其次重点阐述超导磁分离技术在高岭土提纯、矿石选矿、燃煤脱硫、污水处理等领域的应用情况,分析超导磁分离技术应用在上述领域的独特优势,最后展望超导磁分离技术的应用趋势。     

Nonlinear acoustoelectronic interaction in thin superconducting lead films

The effect of high-power surface acoustic waves (SAW) on the superconducting state of Pb films has been studied in different transverse magnetic fields. It was established that a high-intensity sound wave affects the T _c of the film and the character of the superconducting transition, and that the observed changes are the larger, the higher is the SAW intensity. It was found that high-power SAW are capable of inducing vortex depinning in the film and reducing the critical current. Various mechanisms which are responsible for the nature of these effects are discussed. Fiz. Tverd. Tela (St. Petersburg) 39, 1753–1760 (October 1997)     

Magnetic susceptibility of lead sulphide

Magnetic susceptibility measurements were carried out on lead sulphide in the form of natural galena crystals, and in the form of crushed powder. The experimental molecular diamagnetic susceptibility value was found to be 93·27×10^?6 (in e.m.u./gm.mol.) for the single crystal and 81·84×10^?6 for the powdered material. Calculations based on a modified Slater-Angus method showed that the type of bonding is mainly covalent with a partial ionic character.     

Photoemission spectroscopy of the strong-coupling superconducting transitions in lead and niobium

Scanning tunneling microscopy on roughened Au(110) reveals that the equilibrium shape of islands and pits on this surface is almondlike: each island contains two smoothly curved steps joined at two sharp corners. This shape has recently been predicted and finds its origin in the missing-row reconstruction of its fcc (110) surfaces (Au, Pt, etc.). We use the corner angles and the island shapes to determine the step energies. In addition we find that during the decay of an island on the Au(110) surface the shape changes and that the disappearance of the island involves the splitting of the layer below the island into two disconnected regions. The shape change has a dramatic influence on the decay rate of the islands.     

玻璃中CuCl微晶的尺寸量子化激子

通过对尺寸分布非均匀加宽的激子吸收带选择激发的方法,研究了玻璃中几个nm量级的CuCl微晶的激子发光光谱.发现尺寸量子化的激子态劈裂形成多个分量.通过对尺寸量子化所产生的球形微晶中激光跃迁能级劈裂的分析,得到CuCl的z_(1.2)激子跃迁质量,Luttinger参数以及x线性项系数等数据.     

The influence of texturing through zone melting or hot pressing under magnetic fields on the magnetic susceptibility of high temperature superconducting ceramics

Texturing of high-temperature superconducting ceramics leads to an improved intergranular coupling. This is demonstrated on the basis of ac susceptibility measurements obtained when texturing Bi-2223 polycrystals through combined magnetic melt texturing and hot pressing (MMTHP) and Y123 bulk samples obtained through combined magnetic melt texturing and zone melting (MMTZM).     

超导装置电流引线的研究进展

电流引线是连接室温端电源和低温端超导装置的重要部件,也是超导装置热损耗的主要热源之一。选择合适的电流引线形式,并进行引线结构优化设计,可以提高超导装置的可靠性和经济性。概述了电流引线的优化设计目标和分类形式,介绍了全金属电流引线、高温超导电流引线和珀尔帖电流引线的研究进展,分析比较了三类电流引线的工作特点和适用场景,可为超导装置的电流引线选型和优化设计提供参考。