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Theodor H. G. Hehenkamp 《Mikrochimica acta》1992,107(3-6):273-277
In order to optimize the physical properties of HTSC small single crystals grown from a melt for basic studies of their physical properties the influence of the environment on their impurity content was investigated by EPMA. This requires quantitative analysis of all elements being present in the crystals. The accuracy of results was affected by problems with the choice and quality of standards, by contamination but also by malfunction of microprobe electronics. The HTSC materials were found to react with mills, milling balls, crucibles and the atmosphere. These problems are being discussed and some reactions being studied for Y1Ba2Cu3O6+x (0 < x < 1) HTSC in A12O3 and ZrO2 crucibles. The crystals grown contain reproducible amounts of impurities depending on boundary conditions and exhibit a zone structure in composition particularly for Y and Ba within their range of homogeneity. 相似文献
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Abstract The Raman spectra of Y B a2Cu3Ox, single crystals (x=6.25; 6.75; 7.0) were measured at pressures up to 22 GPa (35 GPa for x=6.25) at room temperature in nearly hydrostatic conditions. The frequency-volume curves for most of the Raman-active fundamental vibrations were derived from the present data making use of a previous high-pressure study of the equations of state of Y Ba2 Cu 3 O x compounds. 相似文献
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In an early study the BCS wave function was generalized to include the motion of the center-of-mass of Cooper pairs. An alternative order parameter can be defined on the basis of this motion. In later work, when in copper oxides Bloch orbitals replaced free electrons, nodes were found in the vector space of the Fourier representation of the order parameter. Here that Fourier representation has suggested that the parameter consists of two components, a long wave lengths part which does not contain nodes, a short wave length part which does. The former component is real, and applies deep inside the superconductor, the latter, which is imaginary, in the boundary region. Further, the imaginary component has odd symmetry about the nodal axis. There results an addition of about 0.93π to the relative phase of two adjacent sides of a square superconductor cut along appropriate crystal axis, and embedded in a normal metal. 相似文献
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Cl. Kriebel O. Hoffels R. Borowski H. Gottschalk H. Alexander D. Wohlleben 《Annalen der Physik》1995,507(2):136-143
A new method which allows the detection of the superconducting phase transition of high-Tc superconductors (HTSC) on a microscopic scale is reported. Micro-size holes in thin foils of superconducting material are examined in a transmission electron microscope at varying temperatures. The superconducting transition induces small changes in the image intensity within the holes, which can be detected by using electronic image analysis. Superconducting transition curves are then obtained for various types of high-Tc superconductors and for given values of the applied magnetic field. 相似文献
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I. Puica V. Popescu P. Mazzetti A. Stepanescu Gh. Ciobanu 《Physica C: Superconductivity and its Applications》1997,290(3-4):303-310
The 1/f voltage noise in bulk polycrystalline high-temperature superconductors (HTSC) under bias current and magnetic field has its origin in the noise current-dependence of the grain boundary junctions (GBJs), due in turn to the correlated effects of junction critical current and normal resistance fluctuations. The analogy between the results obtained by varying the bias current through the specimen and those performed with temperature as variable is evidenced. The noise maxima obtained in both sets of measurements turn out to be caused by the junction critical current fluctuations, which dominate when the currents flowing through the GBJs are close to the Josephson critical current. The anti-phase correlation between the normal resistance and the critical current fluctuations is responsible for the monotonical decrease of the noise at constant bias current, with the temperature exceeding the value corresponding to the noise maximum. In contrast, varying the bias current at fixed temperature, the voltage noise exhibits a local minimum followed by an increasing tendency after passing through the maximum. 相似文献
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YBa2Cu3O7– thin films were deposited by pulsed laser deposition (PLD) on various substrates with different misfit. X-ray diffraction (XRD) measurements were performed in order to characterize the growth quality of the films and to study the orientation between the films and the substrates. On the used substrates all investigated films are relaxed independently, and epitaxially grown who show a long range ordered two domain structure. The elemental concentration depth profiles of these films detected by secondary neutral mass spectrometry (SNMS) show homogeneous stoichiometric element distributions with slight deviation of the Y content.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday 相似文献
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N‐band Hubbard models. III. Boson–fermion and interaction–boson models for high‐Tc superconductivity
K. Yamaguchi M. Nakano H. Nagao M. Okumura S. Yamanaka T. Kawakami S. Yamada D. Yamaki Y. Kitagawa R. Takeda H. Nitta 《International journal of quantum chemistry》2006,106(5):1052-1075
In this series of articles (I, II), N‐band Hubbard models have been considered for strongly correlated electron systems, which are realized in d–p, π–d, π–R, and σ–R conjugated systems. The magnetism and superconductivity of these systems have been elucidated in terms of effective exchange integrals (J), which are calculated by first‐principle methods. In part III of this series, the BCS–BEC crossover theory, has been introduced to elucidate the physical foundation of our J and JP model for the high‐Tc superconductivity (HTSC). The boson–fermion (BF) model for this theory is found useful for a reasonable explanation of the experimental phase diagrams of HTSC. The underlying physics of the BF model is different from that of the slave boson field‐theoretical model assuming spinon–holon condensations in the low dimension. The interaction boson model (IBM) for nuclear matter is also employed to describe the cooperative mechanisms of electron–phonon (EP), spin fluctuation (SF), charge fluctuation (CF), and many‐bands (MB) effects. This phenomenological model is useful for pictorial understanding and for the theoretical explanation of the cooperative mechanisms: (EP + SF), (SF + CF), (EP + SF + MB), etc. These are also investigated in analogy to BF model of fermionic gases, where the Feshbach resonance between boson and fermion is responsible for their coupling. The implications of these theoretical results are discussed in relation to recent ALPES and STM experiments for HTSC, which suggest the contributions of SF (J) and EP (P) interactions. The recently discovered superconductivity of boron‐doped diamond is examined as an example of two‐band sigma‐radical (σ–R) conjugated systems. Finally, the bipolaron model is briefly discussed in relation to boson–fermion model via EP interaction to superconductivity. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 相似文献
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