共查询到20条相似文献,搜索用时 15 毫秒
1.
R. Menegotto Costa L. Mendon?a Ferreira V. N. Vieira P. Pureur J. Schaf 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(2):107-113
We have studied experimentally the electrical magneto-conductivity near the
superconducting transition of YBa2Cu3O7-δ, YBa2
(Cu2.95Zn0.05)O7-δ and Y(Ba1.75Sr0.25)Cu3O7-δ polycrystalline samples. The measurements were performed in magnetic fields ranging from 0 to 400 Oe applied parallel to
the current orientation. The results show that the resistive transition of these systems proceeds in two stages. The pairing
transition occurs at the bulk critical temperature Tc, where superconductivity is stabilized within small and homogeneous regions of the
sample generically called grains. The regime of approach to the zero resistance state reveals the occurrence of a coherence
transition at a lower temperature Tc0. This transition is related to the connective nature of the granular samples and is controlled by fluctuations of the
order-parameter phase of individual grains. Our experiments show that the Zn-doping, besides depressing the pairing critical
temperature, strongly enlarges the temperature range dominated by effects related to the coherence transition. The substitution
of Ba by Sr causes only a small reduction of Tc, but also enhances significantly the effects related to the grain
coupling phenomenology. In general, our results indicate that these impurity substitutions in YBa2Cu3O7-δ produce or magnify the granularity at a microscopic level, enhancing the effects of phase fluctuations in the conductivity
near the transition. 相似文献
2.
《Physica C: Superconductivity and its Applications》1999,311(1-2):98-106
We have performed AC magnetic susceptibility measurements as a function of the excitation magnetic field, h, for two YBa2Cu3O7−δ polycrystalline samples using a high-sensitivity home-made susceptometer, for fixed values of the temperature, T, and the external DC magnetic field, H. One of the samples is melt-textured and for H<52.5 Oe it presents features that can be associated with a multilevel granular structure. Using an effective medium model, we have determined the critical current density distribution associated with the multilevel granular structure. The average critical current density in each intergranular region was then calculated by applying Bean's critical state model. 相似文献
3.
We have studied experimentally the in-plane fluctuation conductivity near the superconducting transition in single crystal samples of YBa2Cu3O7, Y0.98Ca0.02Ba2Cu3O7, YBa1.9Sr0.1Cu3O7 and YBa2Cu2.97Zn0.03O7. In order to test the stability of the observed fluctuation regimes, low magnetic fields were applied perpendicular to the Cu-O2 atomic planes. When the transition is approached from above we first observe a three-dimensional (3D) Gaussian regime then a crossover to a genuine critical region where the exponent is consistent with the predictions of the 3D-XY-E universality class. Decreasing further the temperature towards Tc, our results systematically reveal the occurrence of a regime beyond 3D-XY characterized by a very small critical exponent. We propose that this regime is precursory to a weak first-order superconducting transition driven by antiferromagnetic excitations related to the pseudogap phenomenon. The dilution of divalent impurities in YBa2Cu3O7 does not affect the stability of the fluctuation regime beyond 3D-XY and in the case of Ca doping a further approach towards the first-order behaviour is observed. 相似文献
4.
Yuri Aparecido Opata Ezequiel Costa Siqueira Pedro Júnior Rodrigues Alcione Roberto Jurelo 《Phase Transitions》2018,91(4):343-355
In this study, the effects of thermal fluctuations on the electrical conductivity in melt-textured YBa2Cu3O7-δ, Y0.95Pr0.05Ba2Cu3O7-δ and (YBa2Cu3O7-δ)0.95–(PrBa2Cu3O7-δ)0.05 composite superconductor were considered. The composite superconductor samples were prepared through the top seeding method using melt-textured NdBa2Cu3O7-d seeds. The resistivity measurements were performed with a low-frequency, low-current AC technique in order to extract the temperature derivative and analyze the influence of the praseodymium ion on the normal superconductor transition and consequently on the fluctuation regimes. The results show that the resistive transition is a two-step process. In the normal phase, above the critical temperature, Gaussian and critical fluctuation regimes were identified, while below the critical temperature, in the regime near the approach to the zero-resistance state, the fluctuation conductivity diverges as expected in a paracoherent-coherent transition. 相似文献
5.
采用脉冲激光沉积技术,在单晶SrTiO3基底上外延生长了一系列名义结构为p×(NdBa2Cu3O7-δ(m)/YBa2Cu3O7-δ(n))的多层膜和准多层膜(单元层NdBa2Cu3O7-δ较厚而YBa2Cu3O7-δ呈非连贯的岛状分布,m,n为激光脉冲数,p为重复周期).样品的超导转变温度在87—91 K范围,具体大小取决于不同的调制结构,多层膜的重复周期越大,层状界面越多,超导转变温度就越低.磁传输测量表明,准多层的样品不仅具有较高的超导转变温度,而且具有较强的磁通钉扎性能,77K零场下的临界电流密度高达4×106 A/cm2,显示出良好的应用前景.
关键词:
2Cu3O7-δ')" href="#">NdBa2Cu3O7-δ
多层膜
磁通钉扎
临界电流密度 相似文献
6.
Hiroyuki Fujishiro Kiminari Nakasato Shigeo Takahashi Manabu Ikebe 《Czechoslovak Journal of Physics》1996,46(3):1207-1208
The effect of partial replacement of Y site with Ca or Ba site with Sr on the thermal and electrical properties of YBa2Cu3O7?δ superconductors was investigated. For Y(Ba1?XSrX)2Cu3O7?δ system, the characteristic enhancement of the thermal conductivity κ(T) below the transition temperature Tc was decreased more slowly by substitution than that for (Y1?XCaX)Ba2Cu3O7?δ system. Electron-phonon interaction in these systems were discussed based on the phonon heat conduction model under the weak coupling d-wave energy gap. 相似文献
7.
《Solid State Communications》1987,64(2):247-251
Thermal and magnetic measurements have been performed on several YBa2Cu3O7−δ compounds, some ones showing a large content of high Tc (93 K) superconducting phase. A jump in the specific heat ΔCp, is well evidenced at the transition allowing a determination of the ratio ΔCp/Tc ≅ 23 ± 5. mJ/ (mole Cu)K2. In addition, an estimation of the γ value (≅ 11 mJ/(mole Cu). K2) has been drawn from the determination of the electronic entropy at Tc. The samples have been characterized by susceptibility, magnetization and resistivity experiments. The critical field slopes at Tc were found to be dHc1/dT ≅ 17 Oe/K and dHc2/dT ≅ 20 kOe/K. The results are discussed in the framework of the Ginzburg-Landau theory. 相似文献
8.
The epitaxial heterostructures YBa2Cu3O7?δ and YBa2Cu3O7?δ/(5 nm)SrTiO3/BaTiO3/(5 nm)SrTiO3/YBa2Cu3O7?δ are grown by the laser evaporation method on an LaAlO3(100) substrate. The permittivity of a BaTiO3 layer is approximately doubled (T=300 K) when a SrTiO3 thin layer is inserted between a ferroelectric layer and superconducting cuprate electrodes. A maximum in the temperature dependence of the permittivity for a barium titanate layer in the YBa2Cu3O7?δ/(5 nm)SrTiO3/BaTiO3/(5 nm)SrTiO3/YBa2Cu3O7?δ heterostructure is shifted by 70–80 K toward the low-temperature range with respect to its location in the corresponding dependence for the BaTiO3 bulk single crystal. The bias voltage dependence of the permittivity for the BaTiO3 grown layers exhibits a clearly pronounced hysteresis (T=300 K). The superconducting transition temperature for the lower YBa2Cu3O7?δ electrode in a superconductor/ferroelectric/superconductor heterostructure considerably depends on the rate of its cooling after the completion of the formation process. 相似文献
9.
《Current Applied Physics》2015,15(5):617-621
Measured is the transverse electrical resistance of YBa2Cu3O7−δ single crystals with different oxygen deficiency values (δ) in the temperature range Tc − 300 K. The experimental data are approximated by an empiric expression accounting for the fluctuation conductivity near Tc and the semiconductor-like resistance regime. Our analysis of the concentration dependences of the fitting parameters, in particular, reveals that the resistance temperature dependence is largely affected by the sample's non-homogeneity. The latter, in turn, causes a Tc anisotropy and variable-range hopping conductivity between different phases. The deduced maximal values of the basal-plane coherence length, ξxy(0), are comparable with those for low-temperature superconductors. 相似文献
10.
Properties of oxide layers at the interface between Al metal and YBa2Cu3O7−δ ceramics were investigated using X-ray diffraction (XRD), X-ray photoelectron spectra (XPS) and impedance measurements. There have been found the oriented grains having their c-plane parallel to the surface of YBa2Cu3O7−δ. When Al metal was evaporated onto the ceramics sample, the aluminum oxide layer was produced at the interface between Al and YBa2Cu3O7−δ because Al metal oxidizes more easily. The oxygen-deficiency was observed at the ceramics side of the interface as examined by X-ray photoelectron spectra. This oxygen-deficiency can be partly replenished by post annealing whereas it can be fully replenished for the sample to which the mechanical polishing is applied beforehand in order to remove the oriented grains. The thickness of aluminum oxide layer was evaluated by means of the impedance measurements using the alternating current three-terminal method. 相似文献
11.
《Journal of Physics and Chemistry of Solids》2001,62(9-10):1847-1859
A complete solid solution range exists between the systems YBa2Cu3O7−δ and (Pb,Cu)Sr2(Ca,Y)Cu2O7−δ has been found with general stoichiometry (Pb0.75xCu1−0.75x)(Sr2xBa2−2x)(Ca0.5xY1−0.5x)Cu2O7−δ. Energy dispersive spectrometry and X-ray diffraction identified that a true solid solution exists. Superlattice structures observed by electron diffraction across the solid solution range have a modulation range have a modulation periods along a* which can be varied by altering both the compositional parameter x and the overall oxygen content. The existence of these superlattices infers that the solid solution is non-random and therefore thermodynamically non-ideal. The superconducting transition temperatures, Tc, across the solid solution range are also strongly dependent on the composition, x, but no direct relationship with the modulation period has been established. From these studies it may be concluded that the solid solution between known superconductors is possible, although involving some partial ordering of the lattice, but ordering of cations in the rock-salt to charge reservoir layer is not a significant factor in determining the superconducting properities, which depend more closely on the overall composition and hence on the ability of the charge reservoir layer to transfer charge to the superconducting layers. 相似文献
12.
《Solid State Communications》2003,125(7-8):407-411
A systematic study of the weak-link behavior for YBa2Cu3O7−δ polycrystalline samples has been done using the electrical resistivity and AC susceptibility techniques. The experiments were performed with two samples of similar grain, a sample of well-coupled grains, and a deoxygenated sample in such a way that the oxygen mostly comes from the intergrain region. Analysis of the temperature dependence of the AC susceptibility near the transition temperature (Tc) has been done employing Bean's critical state model. The observed variation of intergranular critical current densities (Jc) with temperature indicates that the weak links are changed from superconductor normal–metal superconductor (SNS) for well-coupled samples to superconductor insulator normal–metal–superconductor (SINS) type of junctions for the deoxygenated sample. These results are interpreted in terms of oxygen depletion from grain boundaries, which in turn decreases the intergranular Josephson coupling energy with a concomitant decrease of pinning of the intergranular vortices. 相似文献
13.
Effect of high pressure on the fluctuation paraconductivity in Y0.95Pr0.05Ba2Cu3O7−δ single crystals
R.V. Vovk N.R. Vovk G.Ya Khadzhai O.V. Dobrovolskiy Z.F. Nazyrov 《Current Applied Physics》2014,14(12):1779-1782
The effect of high hydrostatic pressure up to 17 kbar on the fluctuation conductivity of lightly Pr-doped Y1−xPrxBa2Cu3O7−δ (x ≈ 0.05) single crystals is investigated. We show that in contrast to non-doped YBa2Cu3O7−δ samples, application of a high pressure leads to a substantial increase of the pressure derivative of the coherence length dξc/dP and a temperature shift of the 2D-3D crossover point. Possible mechanisms of the influence of high pressure on the critical temperature and the coherence length are discussed within the framework of a model assuming the presence of singularities in the charge carriers electron spectrum typical for lattices with strong coupling. 相似文献
14.
L. A. Openov 《JETP Letters》2005,81(1):39-42
Experiments on the irradiation-induced suppression of the critical temperature in high-T c superconductors are analyzed within the mean-field Abrikosov-Gor’kov-like approach. It is shown that the experimental data for YBa2Cu3O7-δ single crystals can be quantitatively explained by the pair-breaking effects under the assumption of the combined effect of potential and spin-flip scattering on the critical temperature and with an accounting for a nonpure d-wave superconducting order parameter. 相似文献
15.
《Solid State Communications》1987,63(5):385-388
We have performed detailed high temperature X-ray diffraction to study the nature of the structural phase of YBa2Cu3O7−δ. The results indicate the existence of a reversible orthorhombic to tetragonal phase transition at a temperature close to 750°C. If the high temperature tetragonal phase is quenched-in at low temperatures the critical superconducting temperature is considerably reduced from 92.5 K. This suggests that the one dimensional CuO chains present in the orthorhombic structure are necessary for high temperature superconductivity. 相似文献
16.
《Physics letters. A》1987,126(3):205-208
Experimental data on the superconducting critical temperature Tc of YBa2(Cu1−xMx)3O7−y, where M is a 3D transition ion are reviewed and shown to correlate closely with the difference in crystal field stabilization energies for Cu2 sites in the 2D planes and Cu1 sites in the 1D chains respectively. Thus superconductivity is depressed when the 1D chain is modified. 相似文献
17.
《Journal of Physics and Chemistry of Solids》2001,62(9-10):1837-1846
We report the transport studies of YBa2Cu3Oy/YxPr1−xBa2Cu3Oy and YBa2Cu3Oy/R1−xMxMnO3 superlattices in magnetic fields in which R=La or Nd, and M=Ca or Sr. The X-ray diffraction of samples shows superlattice structure. The resistive transition in a magnetic field shows thermal activated behavior. The flux pinning is reduced when the coupling strength between YBCO layers is decreased. The angular dependence of the critical current of YBa2Cu3Oy/PrBa2Cu3Oy superlattices reveals the dimensionality of superlattices. The magnetoresistance ratio (MR), |Δρ(H=7 T)−Δρ(H=0)|/Δρ(H=7 T), of YBa2Cu3Oy/R1−xMxMnO3 superlattices is affected by the layer coupling of R1−xMxMnO3 layers. The enhancement of the MR ratio in the tri-layer YBa2Cu3Oy/La0.7M0.3MnO3/YBa2Cu3Oy film in the low temperature regime is significant and has a value of 33650% at T=75 K. We attribute this enhancement of the MR to the ordering of magnetic moment in ferromagnetic layers in magnetic fields. The results are discussed in terms of existing theories. 相似文献
18.
《Physics letters. A》1987,126(1):55-57
A small amount of Pd addition increases Tc for the YBa2Cu3O7−y oxide. The maximum offset, midpoint and onset temperatures of the YBa2(Cu0.999Pd0.001)3O7−y oxide are 92.1, 95.0 and 105 K, respectively. Excess addition of Pd decreases Tc. The Tc change is consistent with the results of the lattice constants. 相似文献
19.
G. A. Ovsyannikov I. V. Borisenko P. V. Komissinskiĭ Yu. V. Kislinskiĭ A. V. Zaĭtsev 《JETP Letters》2006,84(5):262-266
The electrophysical parameters of superconductor/antiferromagnetic insulator structures based on the Nb/Au/Ca1?x Sr x CuO2/YBa2Cu3O7?δ hybrid heterostructure have been examined. YBa2Cu3O7?δ and Ca1?x Sr x SuO2 epitaxial films are grown by the laser ablation method on NdGaO3 single crystal substrates, the thickness of the Ca1?x Sr x CuO2 layer varies from 20 to 50 nm, and x = 0.15 and 0.5. The superconducting pair potential in the interface between the YBa2Cu3O7?δ superconductor and Ca1?x Sr x CuO2 antiferromagnet is found to penetrate into the antiferromagnet at distances much larger than the coherence length calculated for the ferromagnetic layer. The critical current of the superconducting transition manufactured at such an interface is highly sensitive to the magnetic field. 相似文献
20.
《Journal of Physics and Chemistry of Solids》2001,62(9-10):1861-1870
Low temperature specific heat (LTSH) data on a variety of high-Tc superconductors, such as YBa2Cu3O7, La1−xSrxCuO4, Bi2Sr2CaCu2O8, and Ba0.6K0.4BiO3 are reviewed. The agreement between the experimental data and theoretical predictions, such as T2-dependence of specific heat at zero magnetic field and H1/2-dependence of electronic specific heat is widely discussed within the scenario of d-wave superconductivity. Impurity scattering effects and scaling model on d-wave superconductivity are verified using Zn- and Ni-doped La1−xSrxCuO4. The low energy quasiparticle density of states N(E)=N(0)+E1/2 are deduced from dirty d-wave superconductors. Absence of paramagnetic contribution to LTSH is found both in superconducting and non-superconducting underdoped samples suggesting that a mechanism beyond Kondo screening model maybe required to explain its magnetic property. 相似文献