共查询到20条相似文献,搜索用时 31 毫秒
1.
Using a microwave cavity perturbation technique, we have succeeded in observing cyclotron resonances in the layered Perovskite superconductor Sr2RuO4. Three cyclotron masses are deduced, corresponding to mcγ=9.7me, mcβ=5.8me and mc=4.3 me. A comparison between these values and the effective masses deduced from other techniques provides us with a unique means of gauging the role of Coulomb correlations in the title compound. 相似文献
2.
A hybrid mode of one- and two-surface multipactor on the grooved dielectric surface is studied in detail using both an analytical approach and two-dimensional particle-in-cell(2D PIC) simulations. When the groove width L eE_0/(4πm_ef~2),there are one-surface multipactor and one-order two-surface multipactor on the grooved dielectric surface, and only one slope of the groove has the multipactor anytime. When L eE0/(4πme f~2), both slopes may have the multipactors. The electron surface density of the multipactor discharge has a sharp increase at the length L = eE_0/(4πm_ef~2). 相似文献
3.
Two-loop radiative mechanism, when combined with an U(1)L′ symmetry generated by Le − Lμ − Lτ (=L′), is shown to provide an estimate of Δm2/Δm2atm εme/mτ, where ε measures the U(1)L′-breaking. Since Δm2atm 3.5×10−3 eV2, we find that Δm2 ε10−6 eV2, which will fall into the allowed region of the LOW solution to the solar neutrino problem for ε 0.1. 相似文献
4.
Anomalous magnetotransport phenomena have been observed in θ-(BEDT-TTF)2I3 crystals at temperatures below 15 K. The magnetoresistance M : (1) is a linear function of the magnetic field H, (2) is not affected by the angle between the electric current and the magnetic field, (3) but depends on the magnetic field orientation with respect to the crystal axis. Magnetoresistance is expressed as M = (aH2a + bH2b + cH2c)0-3/2/H in terms of H = (Ha, Hb, Hc), the zero field resistivity 0, and parameters a, b, and c which are independent of temperature and magnetic field. We have found that b a > c. Magnetoresistance up to 40 is observed for H = 7T along the b-axis at T = 1.5K. 相似文献
5.
Considerations concerning the radiative corrections to muon decay in the Fermi and Standard theories
The FAC, PMS, and BLM optimization methods are applied to the QED corrections to the muon lifetime in the Fermi V-A theory. The FAC and PMS scales are close to me, while the BLM scale nearly coincides with the geometric average √memμ. The optimized expressions are employed to estimate the third order coefficient in the (mμ) expansion and the theoretical error of the perturbative series. Using arguments based on effective field theory and a simple examination of Feynman diagrams, it is shown that, if contributions of
(mμ2/MW2) are neglected, the corrections to muon decay in the SM factorize into the QED correction of the Fermi V-A theory and the electroweak amplitude g2/(1 − Δr), both of which are strictly scale-independent. We use the results to clarify how the QED corrections to muon decay and the Fermi constant GF should be used in the SM, and what is the natural choice of scales if running couplings are employed. 相似文献
6.
Philip J. Thomas Jon C. Fenton Guang Yang Colin E. Gough 《Physica B: Condensed Matter》2000,280(1-4):245-246
We present measurements of the intrinsic quasi-particle conductivity along the c-axis of 2212-BSCCO single-crystal mesa structures in the superconducting and normal states. Direct measurement of the mesa temperature enables corrections to be made for self-heating and permits the acquisition of reliable I–V characteristics over a wide range of temperatures and voltages. Unlike a conventional superconductor, there is no evidence for any change in the quasi-particle conductivity at Tc, consistent with precursor pairing of electrons in the normal state. At low temperatures the initial low-voltage linear conductivity exhibits a T2 dependence, approaching a limiting value at zero temperature. 相似文献
7.
J. Wan C. Sheng F. Lu S. Yuan D. W. Gong L. S. Liao Y. L. Fang F. Lin Xun Wang 《Journal of luminescence》1998,80(1-4):369-373
The annealing behaviors of photoluminescence of SiOx and Er-doped SiOx grown by molecular beam epitaxy in the wavelength range of visible and infrared light are studied. For SiOx, four PL bands located at 510, 600, 716 and 810 nm, respectively, are observed. For Er-doped SiOx, the 716 nm band, which is believed to be originated from the electron–hole recombination at the interface between crystalline Si and amorphous SiO2, disappears in the annealing temperature range of 500–900°C. It is suggested the enhancement of Er luminescence is partially due to the energy transfer from the recombination at the interface between crystalline Si and SiO2 to Er ions. 相似文献
8.
P.E. Kazin V.V. Poltavets Y.D. Tretyakov M. Jansen B. Freitag W. Mader 《Physica C: Superconductivity and its Applications》1997,280(4):31-265
Phase evolution in the Bi---Sr---Ca---Cu---Al---O system was studied. Two Al-containing phases BiSr1.5Ca0.5Al2Oz and (Sr1−xCax)3Al2O6 (x = 0.4 − 0.45) were determined to be chemically compatible with Bi2.18Sr2CaCu2O8+x (Bi-2212) at temperatures of the samples processing. The phase equilibria in the title system were investigated above the solidus temperature. The BiSr1.5Ca0.5Al2Oz was found to be in equilibrium only with the melt and the (Sr1−xCax)3Al2O6 phase. This latter aluminate equilibrated with Ca,Sr cuprates, CaO, the Cu-free phase, and the liquid. The melting and solidification in Bi-2212, doped with the aluminate, corresponded to the reversible reaction Bi-2212 + BiSr1.5Ca0.5Al2Oz ↔ (Sr1−xCax)3Al2O6 + liquid. Two sets of superconducting composite materials with initial compositions Bi-2212 + nBiSr1.5Ca0.5Al2Oz and Bi-2212 + m(Sr1−xCax)3Al2O6 were prepared by solidification from the partial melt. The former material was composed mostly of large Bi-2212 lamellas separated by the BiSr1.5Ca0.5Al2Oz phase, which destroyed superconducting links between Bi-2212 grains. The latter material consisted of a Bi-2212 polycrystalline matrix with high concentration of small (ca. 3 μm) grains of (Sr1−xCax)3Al2O6 imbedded in Bi-2212 lamellas. The Bi-2212 + m(Sr1−xCax)3Al2O6 materials displayed a trend to enhance flux pinning at T = 60 K with the increase of aluminate phase content. 相似文献
9.
P. V. Chliapnikov 《Physics letters. [Part B]》1999,470(1-4):263-267
The relative fractions of vector, V, and pseudoscalar, P, primary mesons produced in
and
decays, and primary light-flavour mesons produced in fragmentation processes are explained by the hyperfine mass splitting. The difference in corresponding fractions arises from the difference in the constituent quark masses
, ms, mc and mb:The production ratios for strange, charm and beauty mesons evaluated from the ρ/(3π) ratio, measured at LEP for primary produced ρ and π, agree with the results of LEP and lower energy e+e− experiments. 相似文献
10.
We report on the perturbative O(s) correction to the light-cone QCD sum rule for the B → π transition form factor f+. The correction to the product fBf+ in leading twist approximation is found to be about 30%, that is similar in magnitude to the corresponding O(s) correction in the two-point sum rule for fB. The resulting cancellation of large QCD corrections in f+ eliminates one important uncertainty in the sum-rule prediction for this form factor. 相似文献
11.
Yan Gao Peter Lee James Ye Peter Bush Vaclav Petricek Philip Coppens 《Physica C: Superconductivity and its Applications》1989,160(5-6):431-438
The modulation of the (221) superconducting Bi2Sr2−xCaxCuO6 phase has been analyzed by X-ray diffraction, using four-dimensional symmetry theory. The pseudo-orthorhombic diffraction pattern is a superposition of two twin related components, such that the main reflections with hkl and hk
m superimpose, but the satellite hklm and hk
m do not. The latter feature allows separation of the twin intensities. The modulation analysis in superspace group P:Aa:1 shows displacements similar to those observed in the 2212 compound [Y. Gao et al., Science 241 (1988) 954] but with generally larger displacements. In particular, the c-axis displacement amplitude of the Cu atoms is increased to almost 0.5 Å. This and the obliqueness of the q vector (q=0.214a*+0.61c*) indicate the absence of a restraining influence exerted by the CuO2/Sr(Ca)/CuO2 double layers in the multi-Cu layer phases. 相似文献
12.
A. S. Pine M. Dang-Nhu 《Journal of Quantitative Spectroscopy & Radiative Transfer》1993,50(6):565-570
Intensities have been measured for individual transitions in the Q and R branches of the ν1 band of NH3 using a difference-frequency laser spectrometer. The data yield an integrated band strength of S0v=219.36±1.03 cm-2/MPa at 297 K, corresponding to a transition moment of μv = 8.535(20) × 10-32 C·m, and a Herman-Wallis correction factor, (1 + jm)2, where j = 0.0209(20). The intensities of a few lines for K 7 were noticeably perturbed by a perpendicular Coriolis interaction with 2ν4 (E, L = 2), so were excluded from the fit. A small sample of ν3 band lines occurring in the ν1 band scans also yields a rough estimate of the ν3 band intensity with evident irregular perturbations. 相似文献
13.
V. Kleber 《Progress in Particle and Nuclear Physics》2003,50(2):1115-559
A program to investigate the light scalar resonances a0(980)/ƒ0(980) in hadronic interactions via their decay into the πη and
channels has started at the ANKE spectrometer of COSY-Jülich. As the first step the reactions pp → dπ+X and pp → dK+X have been measured at two energies, Tp = 2.65 GeV and 2.83 GeV. The status of the analysis at Tp = 2.65 GeV is presented. A total cross section of about 50 nb has been determined for the reaction
. 相似文献
14.
Wang Shiwei Qian Yitai Li Rukang Chen Zuyao Wang Nanlin Cao Liezhao Zhou Guien Zhang Yuheng 《Physica C: Superconductivity and its Applications》1993,210(3-4):463-465
Samples of NbSr2Gd2−xCexCu2Oy have been prepared by solid state reaction. The X-ray powder diffraction patterns show that a single phase can be formed in the composition range of 0.49<x<0.51 that has TaSr2 (NdCe)2Cu2Oy structure [1], the cell parameters being a=3.8669±0.0046 Å and c=28.742±0.0048 Å. Superconductivity was found by resistance measurements in the sample of NbSr2Gd1.5Ce0.5Cu2Oy: the onset transition temperature is 27.4 K, and zero resistance appears at approximately 13 K. 相似文献
15.
采用固相反应法制备Sm_(1-x)Ca_xFeO_3(x=0,0.1,0.2,0.3)样品,研究Ca~(2+)掺杂对SmFeO_3介电性能、铁磁性及磁相变温度的影响.X射线衍射图谱分析表明:所有样品的主衍射峰与SmFe03相符合且具有良好的晶体结构.随着x的增加,SmFeO_3样品的晶粒尺寸由原来的0.5μm逐渐增大到2μm.当f=1 kHz时,Sm_(1-x)Ca_xFeO_3(x=0.1,0.2,0.3)样品的ε_r分别是SmFe03的5倍、3倍和2.6倍,而tgσ增大一个数量级.在3T磁场作用下,SmFe03样品的M-H呈线性,随着x的增加,M-H逐渐趋向饱和,Sm_(1-x)Ca_xFeO_3(x=0.1,0.2,0.3)样品的M_r分别是SmFeO_3的20倍、31倍和68倍.X射线光电子能谱分析表明:Fe~(2+)和Fe3+共存于Sm_(1-x)Ca_xFeO_3样品中,Fe~(2+)/Fe~(3+)比例随着x的增加而增大,证明Ca~(2+)掺杂增加了Fe~(2+)的含量,形成Fe~(2+)—O~(2-)—Fe~(3+)超交换作用,增强SmFe03的铁磁特性.测量了Sm_(1-x)Ca_xFeO_3样品在外加磁场为1000 Oe(1 Oe=79.5775 A/m)的M-T变化关系,观测到其自旋重组温度(T_(SR))和尼尔温度(T_N)分别为438 K和687 K,发现SmFe03样品的T_(SR)和T_N均随着x的增加向低温方向移动,当x=0.3时,自旋重组现象消失.这主要是SmFeO_3样品磁结构的稳定性和Fe~(3+)—O~(2-)—Fe~(3+)及Sm~(3+)—O~(2-)—Fe~(3+)超交换三者共同作用的结果. 相似文献
16.
H. M. Luo B. Qu Z. Y. Chen Y. T. Qian W. C. Yu 《Physica C: Superconductivity and its Applications》1996,270(3-4):249-252
New Pb based layered superconducting cuprates (Pb0.5Cd0.5)(Sr0.9R0.1)2(R′0.7Ce0.3)2Cu2Oy with (R,R′) = (Eu,Gd), (Eu,Dy) and (Nd,Gd), have been successfully synthesized. The structure of (Pb,Cd)(Sr,Eu)2(Gd,Ce)2Cu2Oy is determined using XRD data. The X-ray powder diffraction pattern can be indexed by the tetragonal structure with lattice parameters a = 3.8250 Å, C = 29.2235 Å and a space group of I4/mmm. The effects of synthesis conditions on (Pb,Cd)(Sr,Eu)2(Gd,Ce)2Cu2Oy are studied and a Tc(onset) of 26 K is obtained by resistance measurements. It is isostructural to the superconductor (Pb,Cu)(Sr,Eu)2(Eu,Ce)2Cu2Oy. 相似文献
17.
P. Burlet R. Troc D. Kaczorowski H. Noël J. Rossat-Mignod 《Journal of magnetism and magnetic materials》1994,130(1-3):237-241
The magnetic ordering in the tetragonal ternary compound U4Cu4P7 has been studied by neutron diffraction. It orders below TN = 146 K with an antiferromagnetic structure of wave vector k = (001). The magnetic ordering corresponds to a stacking of ferromagnetic (001) uranium planes according to the sequences m1, m1, m2, -m2, -m1, -m1, -m2, m2 where m1 and m2 represent the magnetic moment, directed along the tetragonal axis of the two uranium sites U(1) (0,0,± z1) and U(2) (0,0, ± z2) respectively. The magnetic moments on these two sites have different temperature dependencies as well as well as they reach the different values of 1.1 and 2.2.μB for the U(1) and U(2) sites, respectively. 相似文献
18.
C. Martin J. Hejtmanek Ch. Simon A. Maignan B. Raveau 《Physica C: Superconductivity and its Applications》1995,250(3-4):235-239
The thermoelectric power (TEP) S versus temperature has been systematically investigated for several series of the superconducting cuprates Tl(Ba,Sr)2Cam−1CumO2m+3−δ (m = 2, 3) and Tl2Ba2Cam−1CumO2m+4+δ (m = 1, 2, 3). The consideration of the S(Tc) curves allows two important points to be found evidence for. The first one deals with the fact that all these superconducting thallium cuprates are systematically overdoped whatever Tc, and whatever the number of Cu or Tl layers; no underdoped superconducting cuprate could be obtained. The second point shows that there exist two classes of Tl cuprates: the weakly overdoped cuprates that exhibit a Tc max ≥ 100 K (all the triple copper layer cuprates and the 2212 cuprates) and those which can be heavily doped that exhibit a Tc max ≤ 90 K (the 2201 and the 1212 cuprates). The different behavior of thallium cuprates compared to YBa2Cu3O7−δ and to bismuth cuprates is discussed. 相似文献
19.
Characterization by Auger electron spectroscopy (AES) and Fourier transformation infrared spectroscopy (FTIR) confirms (Ta2O5)x(Al2O3)1−x alloys are homogeneous pseudo-binary alloys with increased thermal stability with respect to end member oxides, Ta2O5 and Al2O3. Capacitance–voltage (C–V) and current density–voltage (J–V) data as a function of temperate show that the Ta d-states of the alloys act as localized electron traps, and are at an energy approximately equal to the conduction band offset of Ta2O5 with respect to Si. 相似文献
20.
S. Nakajima M. Kikuchi T. Oku N. Kobayashi T. Suzuki K. Nagase K. Hiraga Y. Muto Y. Syono 《Physica C: Superconductivity and its Applications》1989,160(5-6):458-460
Superconductivity was observed in La substituted Tl2Ba2CuO6. Both Tc and unit cell dimension, a, increase with increasing La concentration, indicating that an over-doping state in Tl2Ba2CuO6, which was due to charge transfer Tl3−t-(Cu-O)p as supported from XPS measurements, was relieved by La substitution for Ba. 相似文献