共查询到20条相似文献,搜索用时 15 毫秒
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M. Tachiki S. Takahashi F. Steglich H. Adrian 《Zeitschrift für Physik B Condensed Matter》1990,80(2):161-166
The copper oxide superconductors are considered to have stacking structures of strongly and weakly super-conducting layers. Using this model, the tunneling conductance in a junction of the superconductor and a normal metal is calculated as a function of bias voltage. The calculation predicts that a characteristic fine structure appears inside the superconducting gap in the tuneling spectrum at low temperatures. 相似文献
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The zero bias tunneling conductance is investigated theoretically and shown to be a promising experimental tool for detecting first order phase transitions in high field superconductors. We calculate and evaluate numerically the zero bias tunneling conductance for arbitrary spin orbital mean free path. In doing the calculations we distinguish between thin films in a parallel field and high?-value materials in a perpendicular field. In the former case anomalous properties appear for sufficient long spin orbital mean free path. Finally we determine the minimum spin orbital mean free path which is compatible with a first order phase transition and show that it is much smaller than commonly believed. 相似文献
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Local density of states of quasiparticles around the magnetic impurity in superconductors are calculated on the basis of a pair potential the spatial dependence of which is determined self-consistently using negative Hubbard model. The spatial dependence of the tunneling conductance observed by Scanning tunneling spectroscopy (STS) strongly depends on the magnitude of the impurity potentials. 相似文献
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R. Srinivasan V. Sankaranarayanan C. K. Subramaniam Prakash Fortunata Rajam S. Kasiviswanathan Vijayashree Radhakrishnan 《Phase Transitions》2013,86(1-3):87-95
Abstract Resistance and thermopower measurements have been made on a series of compounds, YBa2Cu3- x Zn x O7-y, with x = 0.025, 0.05, 0.1, 0.15 and 0.2. The superconducting transition temperature decreases as the zinc concentration increases. In a range of temperatures below TM , the mid point of the transition, the resistance shows an exponential temperature dependence fitting the phenomenological formula proposed by Ausloos et al. From the plot of logarithm of resistivity vs. (TM ? T) 1/2/T, one deduces a value of the average dimension of the Josephson junction to be a few tens of Å, suggesting the microtwin boundaries to be the location of the junctions. The thermopower shows a peak always just above Tc . This conclusively shows that phonon drag is not the cause of the peak. The temperature dependence of the thermopower appears to resemble closely the earlier observations of Srinivasan et al. on yttrium barium copper oxide. Single-particle tunneling measurements carried out for two concentrations, x = 0 and 0.05, appear to indicate that the energy gap parameter scales with Tc , and 2Δ/kTc has an approximate value of 5.5. 相似文献
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The quenched decorated Ising model with competitive interactions is used here to described the magnetic properties of the copper oxide superconductors compounds in the insulating phase (antiferromagnetic). The model consists of planes in which the nodal spins interact antiferromagnetically (JA<0) with their nearest-neighbors, and ferromagnetically (JF>0) with the spins that decorate the bonds, which are quenched and distributed randomly over the two-dimensional lattice. The planes interact antiferromagnetically with weak-exchange interaction (i.e., , λ=10-5). By using the framework of an effective-field theory, based on the differential operator technique, we discuss the antiferromagnetic-phase stability limit in the temperature-decorated bond concentration space (T-p), for λ=10-5 and various values of frustration parameter α=JA/JF. For certain region range of the parameter α we observe a reentrant behavior at low-temperature. We also discuss the critical behavior of TN versus α for some values of decorated bond concentrations and reentrant phenomena is observed. We calculate the dependence of the staggered magnetization as a function of the temperature to analyze the reentrant behavior observed in the phase diagrams. 相似文献
10.
A. C. Sharma 《Solid State Communications》1989,70(12):1171-1174
We present a model calculation of the effective interaction between the charge carriers in YBa2Cu3O7−δ and other related copper oxide superconductors. Our calculation shows that the plasmons (electronic excitations) play a dominant role in producing high superconducting transition temperatures in these materials. 相似文献
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A flux liquid serves as a model for the Abrikosov phase of a type II superconductor with short coherence length and strong fluctuations. Here we discuss the effect of anisotropy due to the planes in the material and disorder due to impurities in terms of the density-density correlation function. We find that both effects change the qualitative behavior of the correlation lengths. 相似文献
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C. P. Slichter S. E. Barrett J. A. Martindale D. J. Durand C. H. Pennington C. A. Klug K. E. O’Hara S. M. DeSoto T. Imai J. P. Rice T. A. Friedmann D. M. Ginsberg 《Applied magnetic resonance》1992,3(3-4):423-448
The authors review and up-date their work on Knight shifts, spin-lattice relaxation, and indirect nuclear spin-spin coupling for YBa2Cu3O7 in the superconducting state. The data are analyzed in particular to show what it may indicate about the orbital and spin pairing of the superconducting state. 相似文献
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We address here the self-consistent calculation of the spin density wave and the charge density wave gap parameters for high-Tc cuprates on the basis of the Hubbard model. In order to describe the experimental observations for the velocity of sound, we consider the phonon coupling to the conduction band in the harmonic approximation and then the expression for the temperature dependent velocity of sound is calculated from the real part of the phonon Green’s function. The effects of the electron–phonon coupling, the frequency of the sound wave, the hole doping concentration, the CDW coupling and the SDW coupling parameters on the sound velocity are investigated in the pure CDW phase as well as in the co-existence phase of the CDW and SDW states. The results are discussed to explain the experimental observations. 相似文献
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We discuss the different regimes which can be expected for quantum creep of flux lines by analysing the experimental results obtained for the relaxation rate as T→0 for Y1Ba2Cu3O7, Bi2Sr2Ca1Cu2O8 and (ET)2Cu(NCN)2Br single crystals. We address the dimensionality of the pinned flux line, the possible bundle regime at high fields for the organic superconductor and the relative invariability of the quantum rate upon introduction of columnar defects. 相似文献
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The influence of spin and charge fluctuations on the pseudogap formation in cuprate superconductors has been studied using
the diagram technique for Hubbard operators. It has been shown that the joint inclusion of the spin and charge fluctuations
leads to the formation of “shadow” bands with a strong modulation of the spectral intensity and to a decrease in the density
of electronic states at the Fermi level. 相似文献
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Shiping Feng Zheyu HuangHuaisong Zhao 《Physica C: Superconductivity and its Applications》2010,470(21):1968-1976
Within the t–t′–J model, the doping dependence of the Meissner effect in cuprate superconductors is studied based on the kinetic energy driven superconducting mechanism. Following the linear response theory, it is shown that the electromagnetic response consists of two parts, the diamagnetic current and the paramagnetic current, which exactly cancels the diamagnetic term in the normal state, and then the Meissner effect is obtained for all the temperature T ? Tc throughout the superconducting dome. By considering the two-dimensional geometry of cuprate superconductors within the specular reflection model, the main features of the doping and temperature dependence of the local magnetic field profile, the magnetic field penetration depth, and the superfluid density observed on cuprate superconductors are well reproduced. In particular, it is shown that in analogy to the domelike shape of the doping dependent superconducting transition temperature, the maximal superfluid density occurs around the critical doping δ ≈ 0.195, and then decreases in both lower doped and higher doped regimes. 相似文献