New determination of the fine structure constant from the electron value and QED

Quantum electrodynamics (QED) predicts a relationship between the dimensionless magnetic moment of the electron (g) and the fine structure constant (alpha). A new measurement of g using a one-electron quantum cyclotron, together with a QED calculation involving 891 eighth-order Feynman diagrams, determine alpha(-1)=137.035 999 710 (96) [0.70 ppb]. The uncertainties are 10 times smaller than those of nearest rival methods that include atom-recoil measurements. Comparisons of measured and calculated g test QED most stringently, and set a limit on internal electron structure.     

New measurement of the electron magnetic moment and the fine structure constant

A measurement using a one-electron quantum cyclotron gives the electron magnetic moment in Bohr magnetons, g/2=1.001 159 652 180 73 (28) [0.28 ppt], with an uncertainty 2.7 and 15 times smaller than for previous measurements in 2006 and 1987. The electron is used as a magnetometer to allow line shape statistics to accumulate, and its spontaneous emission rate determines the correction for its interaction with a cylindrical trap cavity. The new measurement and QED theory determine the fine structure constant, with alpha{-1}=137.035 999 084 (51) [0.37 ppb], and an uncertainty 20 times smaller than for any independent determination of alpha.     

Structural investigations of Ge(5)As(x)Se(95-x) and Ge(15)As(x)Se(85-x) glasses using x-ray diffraction and extended x-ray fine structure spectroscopy

The structure of Ge(5)As(x)Se(95-x) (x?=?10, 20, 30, 38?at.%) and Ge(15)As(x)Se(85-x) (x?=?10, 25, 34?at.%) glasses has been investigated by high-energy x-ray diffraction and extended x-ray absorption fine structure measurements. The experimental datasets have been modelled using the reverse Monte Carlo simulation technique. The model atomic configurations have been analysed in detail. It has been found that the homonuclear Ge-Ge, As-As, Se-Se and heteronuclear Ge-As bonds play an important role in the structure formation of the Ge-As-Se glasses. The total number of these bonds decreases quite slowly with the mean coordination number similarly to the nonlinear refractive index.     

Electronic structure of the organic semiconductor copper tetraphenylporphyrin (CuTPP)

The electronic structure of thin films of the organic semiconductor copper tetraphenylporphyrin (CuTPP) has been studied using synchrotron radiation-excited resonant soft X-ray emission spectroscopy (RSXE), near edge X-ray absorption fine structure (NEXAFS) spectroscopy, and X-ray photoemission spectroscopy (XPS). The C and N partial density of states for both the valence and conduction band electronic structure has been determined, while XPS was used to provide information on the chemical composition and the oxidation states of the copper. Good agreement was found between the experimental measurements of the valence and conduction bands and the results of density functional theory calculations.     

A study of the radiation from Am241

The radiation from the alpha decay of Am²⁴¹ has been investigated by studying the fine structure of the alpha spectrum and by performing alpha-gamma and gamma-gamma coincidence measurements. For the daughter nucleus Np²³⁷ a level scheme is proposed which comprises 21 excited states and 39 gamma transitions. Evidence was found for the existence of previously unknown gamma rays at (80), 82, 88, (90), 100, 150 (two transitions), 170, (~210), 295, (300), 360, 420, 460 and 690 keV, as well as for the probable occurrence of a new fine structure alpha group at 4754 keV corresponding to a level at 804 keV. For the alpha groups and for most of the gamma rays absolute intensities are given. For some transitions theK-conversion coefficients and multipolarities were determined. The results are discussed within the framework of the unified model. The level density agrees well with the predictions of the superfluid model and is approximately twice the density yielded fromNilsson's theory.     

Order alpha(7)ln(1/alpha) contribution to positronium hyperfine splitting

The logarithmically enhanced alpha(7)ln(1/alpha) contribution to the hyperfine splitting of the positronium ground-state energy levels is calculated in the framework of dimensionally regularized nonrelativistic quantum electrodynamics. The correction is negative and amounts to about 1/3 of the leading logarithmic alpha(7)ln (2)(1/alpha) one. The discrepancy between the experimental measurements and the theoretical prediction is reduced.     

Methods for constraining fine structure constant evolution with OH microwave transitions

We investigate the constraints that OH microwave transitions in megamasers and molecular absorbers at cosmological distances may place on the evolution of the fine structure constant alpha=e(2)/ variant Planck's over 2pi c. The centimeter OH transitions are a combination of hyperfine splitting and lambda doubling that can constrain the cosmic evolution of alpha from a single species, avoiding systematic errors in alpha measurements from multiple species which may have relative velocity offsets. The most promising method compares the 18 and 6 cm OH lines, includes a calibration of systematic errors, and offers multiple determinations of alpha in a single object. Comparisons of OH lines to the HI 21 cm line and CO rotational transitions also show promise.     

Extended X-ray absorption fine structure measurements of laser-shocked V and Ti and crystal phase transformation in Ti

Extended x-ray absorption fine structure (EXAFS), using a laser-imploded target as a source, can yield the properties of laser-shocked metals on a nanosecond time scale. EXAFS measurements of vanadium shocked to approximately 0.4 Mbar yield the compression and temperature in good agreement with hydrodynamic simulations and shock-speed measurements. In laser-shocked titanium at the same pressure, the EXAPS modulation damping is much higher than is warranted by the predicted temperature increase. This is shown to be due to the alpha-Ti to omega-Ti crystal phase transformation, known to occur below approximately 0.1 Mbar for slower shock waves.     

Complex angular dependence of exchange bias on (001) epitaxial NiO-Co bilayers

We have sputter-deposited NiO-Co bilayers on MgO(001) substrates. NiO and Co grow epitaxially on MgO and reproduce its fcc structure. The high quality of our samples, in terms of flatness and crystallographic coherence of the interface, allows the observation of an additional fourfold magnetic anisotropy term by standard magnetometry. This term is induced by interfacial interaction assigned to the same origin as exchange bias. Additional measurements of exchange bias azimuthal dependence versus the crystallographic axes of the film plane reveal unusual behaviors with several sign changes related to this fourfold anisotropy.     

Pressure and temperature dependences of the elastic properties of rutile (TiO2)

Using ultrasonic techniques we have measured the pressure and temperature dependences of the six elastic constants of single-crystalline rutile (TiO₂). The pressure measurements were made in the range 0–20 kbar at room temperature, and the temperature measurements were made in the range 80–300°K at atmospheric pressure. Our results are in good agreement with the results recently reported by Manghnani et al., although our pressure derivatives are generally a few per cent smaller than theirs and our temperature derivatives a few per cent more negative (at 298°K). Nonlinear pressure dependences were observed for some of the elastic constants. A relation between the pressure-induced softening of two lattice modes (one optic and one acoustic) and a possible pressure-induced transition to the CaCl₂ structure is discussed. An approximate separation of the isobaric temperature derivatives of the elastic constants into “pure” volume and temperature contributions is considered. In particular, an attempt is made to estimate the magnitude of the error made in effecting this separation using equations applicable to cubic rather than tetragonal symmetry. It is shown that, in principle, these errors could be significant.     

Non-Fermi liquid states in the pressurized CeCu2(Si1-xGex)2 system: two critical points

In the archetypal strongly correlated electron superconductor CeCu2Si2 and its Ge-substituted alloys CeCu2(Si1-xGex)2 two quantum phase transitions--one magnetic and one of so far unknown origin-can be crossed as a function of pressure. We examine the associated anomalous normal state by detailed measurements of the low temperature resistivity (rho) power-law exponent alpha. At the lower critical point (at pcl, 1相似文献   

Random alloy-like local structure of Fe(Se, S)(1-x)Te(x) superconductors revealed by extended x-ray absorption fine structure

The local structure of Fe(Se, S)(1-x)Te(x) ternary (11-type) chalcogenides has been studied by temperature dependent Fe K-edge extended x-ray absorption fine structure measurements. We find that the Fe-Se and Fe-Te distances in ternary FeSe(1-x)Te(x) are closer to the respective distances in the binary systems, revealing significant divergence of the local structure from the average one. The mean square relative displacements show a systematic change with Te content, consistent with bond relaxation in the inhomogeneous ternary phases. Also, the Fe-Te and Fe-S distances in the FeS(0.2)Te(0.8) ternary system are found to be different in the crystallographically homogeneous structure. The observed features are characteristic of ternary random alloys, suggesting that a proper consideration should be given to the atomic distribution for describing the complex electronic structure of these multi-band Fe-based chalcogenides.     

Revised value of the eighth-order contribution to the electron g-2

The contribution to the eighth-order anomalous magnetic moment (g-2) of the electron from a set of diagrams without closed lepton loops is recalculated using a new FORTRAN code generated by an automatic code generator. Comparing the contributions of individual diagrams of old and new calculations, we find an inconsistency in the old treatment of IR subtraction terms in two diagrams. Correcting this error leads to the revised value -1.9144(35)(alpha/pi)4 for the eighth-order term. This theoretical change induces the shift of the inverse of the fine structure constant by -6.411 80(73)x10(-7).     

钠原子nd高Rydberg系列能级精细结构的计算研究

采用一种新的数值计算方法求解原子体系的相对论Hartree-Fock（RHF）方程.给出了Breit作用中迟滞项的非常清晰、简洁的表示形式.利用建立起来的理论方法和计算程序,计算了Na原子nd（n=17—31）系列能级的精细结构.有别于其他理论计算中多采用微扰论方法,用RHF方法通过自洽迭代直接求解精细结构的能级分裂值,得到了与实验值基本一致的精细结构倒置的计算结果.结果表明相对论架构下原子实电子与价电子的交换作用是导致精细结构反转的主要原因.用微扰方法计算了精细结构分裂中的Breit效应, 关键词： 精细结构 Na原子 相对论Hartree-Fock（RHF）方程 Breit效应     

Phase transition of solid bismuth under high pressure

As a widely used pressure calibrator, the structural phase transitions of bismuth from phase I, to phase II, to phase III,and then to phase V with increasing pressure at 300 K have been widely confirmed. However, there are different structural versions for phase III, most of which are determined by x-ray diffraction(XRD) technology. Using x-ray absorption fine structure(XAFS) measurements combined with ab initio calculations, we show that the proposed incommensurate composite structure of bismuth of the three configurations is the best option. An abnormal continuous increase of the nearest-neighbor distance of phase III with elevated pressure is also observed. The electronic structure transformation from semimetal to metal is responsible for the complex behavior of structure transformation.     

类锂体系激发态1s2 nd(n=3,4,5)精细结构和项能的理论计算

使用全实加关联(fullcorepluscorrelation缩写为FCPC)和里兹(Ritz)变分方法计算了类锂体系(Z=11—20)激发态1s2nd(n=3,4,5)的非相对论能量和波函数;包括动能修正、电子电子接触项、轨道轨道相互作用项以及Darwin项的相对论修正和质量极化项由全实加关联波函数的一阶微扰给出,量子电动力学(quantumelectronicdynamics缩写为QED)修正由有效核电荷方法和类氢公式计算;给出了高电离类锂体系激发态的激发能、精细结构和项能(termenergy),并 关键词： 类锂体系 全实加关联 精细结构 激发能     

High resolution NEXAFS studies of aromatic molecules adsorbed and condensed on Ni(111)

High resolution near-edge X-ray absorption fine structure measurements have been performed on benzene, pyridine and pyrazine adsorbed and condensed on Ni(111). The carbon K-edge multilayer data show the splitting of the e_2u level of benzene into b₁ and a₂ levels for pyridine and into b_3u and a_u levels for pyrazine; the corresponding π resonances are asymmetric due to the vibrational fine structure. At the nitrogen K-edge the transitions into the a₂ and a_u levels are not observed. The benzene data suggest that the Rydberg orbitais are quenched in the condensed phase and that the broad structure above a photon energy of ~ 300 eV is made up of (at least) two σ resonances. On adsorption the π resonances are considerably broadened at the adsorption edges of atoms which interact strongly with the substrate.     

Strange-quark mass from tau-lepton decays with O(alpha3s) accuracy

The first complete calculation of the quadratic quark mass correction to the correlator of the two currents relevant for the strangeness-changing semihadronic tau-decay rate is presented including its real part at the four-loop level. This allows us to perform the extraction of the strange-quark mass m(s) from the decay width of the tau-lepton with full O(alpha3s) accuracy. In agreement with previous estimates, the newly computed alpha3s term proves to be rather large. This justifies inclusion of the similarly estimated alpha4s term in phenomenological analysis. Combined with an updated value of V us and an "improved" version of the renormalization group improvement of the perturbative series, this leads to an increase of the central value of m(s) by about 20% and a partial reduction of the theoretical uncertainty by about 50%.     

Structural and superconducting properties of LaFeAs_(1-x)Sb_xO_(1-y)F_y

We report the antimony(Sb) doping effect in a prototype system of iron-based superconductors LaFeAsO1-yFy(y=0,0.1,0.15).X-ray powder diffraction indicates that the lattice parameters increase with Sb content within the doping limit.Rietveld structural refinements show that,with the partial substitution of Sb for As,the thickness of the Fe2As2 layers increases significantly,whereas that of the La2O2 layers shrinks simultaneously.So a negative chemical pressure is indeed "applied" to the superconducting-active Fe2As2 layers,in contrast to the effect of positive chemical pressure by the phosphorus doping.Electrical resistance and magnetic susceptibility measurements indicate that,while the Sb doping hardly influences the SDW anomaly in LaFeAsO,it recovers SDW order for the optimally-doped sample of y=0.1.In the meantime,the superconducting transition temperature can be raised up to 30 K in LaFeAs1-xSbxO1-yFy with x=0.1 and y=0.15.The Sb doping effects are discussed in term of both J1-J2 model and Fermi Surface(FS) nesting scenario.     

Precision atomic spectroscopy for improved limits on variation of the fine structure constant and local position invariance

We report tests of local position invariance and the variation of fundamental constants from measurements of the frequency ratio of the 282-nm 199Hg+ optical clock transition to the ground state hyperfine splitting in 133Cs. Analysis of the frequency ratio of the two clocks, extending over 6 yr at NIST, is used to place a limit on its fractional variation of <5.8x10(-6) per change in normalized solar gravitational potential. The same frequency ratio is also used to obtain 20-fold improvement over previous limits on the fractional variation of the fine structure constant of |alpha/alpha|<1.3x10(-16) yr-1, assuming invariance of other fundamental constants. Comparisons of our results with those previously reported for the absolute optical frequency measurements in H and 171Yb+ vs other 133Cs standards yield a coupled constraint of -1.5x10(-15)相似文献