Anisotropy of the superconducting critical magnetic field HC2 of LaMCuO system(M = Sr and Ba)

Preliminary measurement of the superconducting critical magnetic field H_c2 of LaMCuO system (M = Sr and Ba) with layered perovskite structure has been carried out. The results show a quite large anisotropy of H_c2 indicating that the present system has a two dimensional character of the electron transport. The measured conductivities seem to be consistent with the values estimated from the observed H_c2 by use of an ideal two dimensional band with free electron mass.     

A new superconducting oxide GdBaCuO with Tc (ρ=0) above 92K

A new superconducting oxide Gd_xBa_1−xCuO_3−y with T_c (ρ=0) above 92K has been successfully synthesized by the ceramic technology. The samples with composition of x=0.5, 0.625 and 0.9 are all observed with high T_c superconductivity. The highest T_c for samples measured is observed in Gd_0.5Ba_0.5CuO_3−y which has a resistive midpoint of 95K with a width of 1.5K, and a zero-resistance temperature of 92.5K. The results of a.c. magnetic susceptibility measurement are also reported.     

On the nature of the valence transition in Eu(Pd1−xAux)2Si2

The intermediate valent compound series Eu(Pd_1−xAu_x)₂Si₂ has been studied by Mössbauer effect measurements on ¹⁵¹Eu(T = 4.2−300K) and ¹⁹⁷Au (4.2K) and by X-ray diffraction (10K, 300K). The temperature induced valence transition Eu²⁺ → Eu³⁺ for x < 0.175 is not of first order type, as suggested in a previous phase diagram [1]. The valence change of the Eu-ion is reflected also in the isomer shift of the ¹⁹⁷Au Mössbauer-resonance.     

Ionic conductivity of ZrF4BaF2MX (M = Li,Na;X = F,Cl) glasses

Glasses were prepared in a wide range of compositions for the two systems oof mixed-cation, ZrF₄BaF₂LiFNaF, and mixed-anion, ZrF₄BaF₂LiFLiCl. Ionic conductivities were measured for these glasses and it was found that these glasses were not only cationic but also anionic conductors depending on the total alkali halide content. Four types of mixed-cation and mixed-anion effects on ionic conductivity were demonstrated for the cation-conducting and anion-conducting glasses. In cation conduction, the cation mixing caused the conductivity decline, whereas the anion mixing led to the conductivity enhancement. In anion conduction, on the other hand, the cation mixing led to the conductivity enhancement, whereas the anion mixing caused the conductivity decline.     

Superconductivity in the LnBaCuO system (Ln = Y,Ho, Er)

Superconductivity around 90K is observed in mixed and single phase system of LnBaCuO (Ln = Y, Ho, Er). Resistivity, X-ray powder diffraction and AC susceptibility measurements were carried out on samples of the mixed phase systems Ln_2−xBa_xCuO_4−y (Ln = Ho, Er), Y_1.2Ba_0.8Cu_1+xO_4+x−y(0<x<5) and single phase system Ba₂LnCu₃O₇ (Ln = Y, Ho, Er). Ln_2−xBa_xCuO_4−y consists of Ba₂LnCu₃O₇, BaCuLn₂O₅, Cu₂Ln₂O₅ and starting materials and shows a small diamagnetic signal below T_c in the temperature dependent AC susceptibility. Y_1.2Ba_0.8Cu_1+xO_4+x−y is a mixture of Ba₂YCu₃O₇, BaCuY₂O₅ and CuO and also indicates a small diamagnetic signal at 92K. Interesting resistivity anomalies occur in the Y_1.2Ba_0.8Cu₄O_7−y and Ho_0.8Ba_1.2CuO_4−y composites including large drops in the resistivity at ∼220 and ∼120K, respectively. The pure compounds, Ba₂LnCu₃O₇ (Ln = Y, Ho, Er) show sharp resistive superconducting transitions and bulk Meissner effects of 90%.     

Oxidation of Si(1 1 1) promoted by K multilayers: K and SiO2 islands

In the context of the alkali-metal promotion of Si oxidation, high-pressure oxidation of potassium multilayers on cooled Si(111) has been investigated using SEM, micro-AES and AFM. The oxidation process at high pressure turns the potassium islands observed at high coverage into potassium oxides islands. A subsequent potassium desorption at moderate temperature (900 K) yields SiO₂ islands (height of 20 nm and lateral dimensions of 10 m) surrounded by a thin continuous SiO₂ overlayer. Other conditions such as potassium multilayer coverage exposed to a low O₂ pressure, potassium monolayer or simultaneous potassium/oxygen adsorption yield a uniform SiO₂ overlayer.     

Electromotive force of a COCO2 sensor in COCO2H2H2O atmospheres and simultaneous determination of partial pressures of CO and CO2

The electromotive force (EMF) of the COCO₂ sensor using Na₂CO₃ and NASICON (Na₃Zr₂Si₂PO₁₂) as solid electrolytes has been examined in COCO₂Ar atmospheres. The EMF is related to the partial pressures of CO and CO₂ and proportional to log(P²_CO2P⁻¹_CO). The simultaneous use of the oxygen sensor of stabilized zirconia gives the EMF proportional to log(P_CO2P⁻¹_CO). The EMF's of two sensors permit to determine individually partial pressures of CO and CO₂. The existence of H₂ with high concentration does not affect the EMF's. This fact proves the applicability of the two-sensor system to the monitoring and the controlling of reducing atmospheres in industrial processes.     

Blocking Effect and Moments of Inertia of K = 1／2 Rotational Band in ^171Yb

The K=1/2 rotational band in ¹⁷¹Yb is investigated using the particle number conserving (PNC) method for treating the cranked shell model with monopole and quadrupole pairing interactions. The experimental moments of inertia of ¹⁷¹Yb [521]1/2 (signature α =±1/2) are reproduced well by the PNC calculation, in which no free parameter is involved. The difference in the contribution to the moment of inertia between protons and neutrons is mainly due to the blocking effect of neutron normal orbitals. The ω variation of the occupation probability of each cranked orbital and the contribution to the moment of inertia from each major shell and from each cranked orbital are investigated.     

Collective-pair structure of Kπ = 0+,1+,2+ bands in deformed nuclei

In the framework of the microscopic IBM the fermion pair structure for several collective excitations has been investigated. In this study the deformed nucleus ¹⁵⁶Gd is treated as an example. The theoretical method used consists of a combination of a triaxial Hartree-Fock-Bogoliubov method and a Hill-Wheeler method. We discuss the effects of keeping the structure of the collective S-, D- and G-pairs fixed as well as varying these structures. The combination of fixed S-, D-, and G-pairs with only one other set of S'-, D'- and G'-pairs is also investigated.     

Influence of sample geometry on the magnetic-field induced metal-insulator transition in nHgCdTe

We report on measurements of the Hall-resistivity as a function of sample geometry in n-Hg_0.8Cd_0.2Te. The results demonstrate that the data measured with an nHgCdTe sample by Shayegan et al.¹ quite recently are a mere consequence of the sample geometry and do not represent the Hall resistivity. The magneto-transport properties of pure n-HgCdTe are not identical with those of n-InSb in strong magnetic fields and at low temperatures.     

Soliton energy band for the six-fold degenerated CDW in the K2Pt(CN)4Br0.3·3.2H2O system

The formation of soliton bands in the quasi-one-dimensional mixed valence planer platinum compound K₂Pt(CN)₄Br_0.3·3.2H₂O (KCP) as a result of overlapping soliton wave functions is considered. A solitonic energy band dependence on temperature and the associated phonon modes of the soliton array are suggested to be responsible for the ESR linewidth broadening observed in this material for temperatures above 85 K.     

Theoretical study of the superhyperfine parameters for Cu2 + in K2PdX4 (X = Cl, Br)

The superhyperfine parameters T _j (j?=?x, y, z) for Cu^2?+? in the square-planar K₂PdX₄ (X = Cl, Br) are theoretically studied from the perturbation formulas of these parameters for an octahedral 3d⁹ cluster, by considering both the contributions from the crystal-field and charge-transfer mechanisms. The related molecular orbital coefficients are determined from the cluster approach in a uniform way. Based on one adjustable proportional factor ρ for the orbital admixture coefficients, the calculated results of present work show reasonable agreement with the observed values.     

High-pressure synthesis of superconducting Nb1−xB2 (x=0–0.48) with the maximum Tc=9.2 K

Superconductivity with T_c above 9 K was found in metal-deficient NbB₂ prepared under 5 GPa, while no clear superconductivity was observed down to 3 K in stoichiometric NbB₂. The superconductivity was observed above x=0.04 in Nb_1−xB₂, and the lattice parameters also changed abruptly at x=0.04. As x increased, the transition temperature T_c slightly rose and fell with the maximum value of 9.2 K at x=0.24 for the samples sintered at 5 GPa and 1200 °C. The T_c-value changed in the range from 7 to 9 K, depending on the sintering pressure. A series of Ta_1−xB₂ (0⩽x⩽0.24) was also synthesized under high pressure to examine a special effect of high-pressure synthesis.     

Quantum interference effects in a multidriven transition Fg=3←→Fe=2

We have theoretically and experimentally studied the quantum coherence effects of a degenerate transition Fg =3←→Fe=2 system interacting with a weak linearly polarized （with σ＋ components） probe light and a strong linearly polarized （with σ＋ components） coupling field. Due to the competition between the drive Rabi frequency and the Zeeman splitting, electromagnetically induced transparency （EIT） and electromagnetically induced absorption （EIA） are present at the different values of applied magnetic field in the case where the Zeeman splitting of excited state Δe is larger than the Zeeman splitting of ground state Δg （i.e.Δe 〉 Δg）.     

Precision measurement of the (3p–1s) X-ray transition in muonic hydrogen

The (3p — 1s) X-ray transition to the muonic hydrogen ground state was measured with a highresolution crystal spectrometer. The assumption of a statistical population of the hyperfine levels of the muonic hydrogen ground state was directly confirmed by the experiment and measured values for the hyperfine splitting can be reported. The measurement supplements studies on line broadening effects induced by Coulomb de-excitation hindering the direct extraction of the pion-nucleon scattering lengths from pionic hydrogen and deuterium X-ray lines.     

从S(u)曲线探讨T=±OK,T=±∞K 状态的特性

本文从Ｓ（ｕ）曲线探讨Ｔ＝±ＯＫ，Ｔ＝±∞Ｋ四个极端状态的特性．文中讨论了在Ｔ＝±ＯＫ及Ｔ＝±∞Ｋ时ＧＸ＝０，因此这四个极端状态均不能作为“热库”，均无热功转换的特性，不存在包含任一状态的卡诺循环．但是却存在类似于能氏定理的ｌｉｍ（△ｓ）ｒ＝０及ｌｉｍ Ｔ＝－ＯＫ Ｔ＝＋∞Ｋ（△ｓ）Ｔ＝０的公式．本文还对研究这些极端状态的必要性与重要性进行了探讨．     

Isomer shift of the electrically split 6.2 keV nuclear transition of Ta181 in CuTaS3

The isomer shift of the 6.2 keV nuclear transition of Ta181 in CuTaS₃RAIN was investigated by nuclear gamma resonance spectroscopy. Relative to tantalum metal the isomer shift in CuTaS₃ corresponds to +37.95±0.1 mm/s. The z component of the electric field gradient at the nuclear site of Ta181 was found to be V_zz = (−1.29±0.01)·10¹⁸ v/cm². The close correlation between the isomer shift in CuTaS₃ and the electronegativity of the Ta-ligands is pointed out.