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101.
考虑铁基超导中能带间的相互作用和界面对每一个能带的散射作用, 利用推广的Blonder-Tinkham-Klapwijk模型, 并通过求解Bogoliubov-de Gennes 方程研究了具有不同类型双能隙系统的量子线/铁基超导隧道结中准粒子的输运系数和隧道谱. 研究表明: 1)在弹道极限时, 随着带间相互作用的增大, s± 波隧道谱中零偏压附近的平台演变成电导峰; s++ 波的平台演变成凹陷; p波的零偏压电导峰被压低. 2)界面对两个能带的散射作用不为零时, 随着带间相互作用的增大, s± 波和s++ 波两能隙处的峰值将降低, 而两峰间的凹陷值将变大; p波的零偏压电导峰被压低, 非零偏压电导增大. 3)界面对每个能带的散射, 可使其产生的电导峰变得更加尖锐, 但可压低和抹平另一个带产生的电导峰值. 这些结果对于澄清铁基超导体的能隙结构和区别不同类型铁基超导体有所帮助. 相似文献
102.
The implementation of a heating element to a composite gasket for high-temperature applications in the diamond-anvil cell was developed based on a double-gasket assemblage. The heating element is a thin platinum wall that covers the central borehole of the metal–ceramic–metal composite gasket and interconnects the two metal component parts of the gasket. Applying electric powers up to 35 W to the two gasket metal components result in ring-like heating around the sample inside the pressure chamber with temperatures exceeding ~2000 K in individual cases. The ring-like distribution of the maximum temperature located at the pressure-chamber wall facilitates a homogeneous temperature distribution at the sample position. As a consequence of the concentration of the heating power to the pressure chamber region, gradients of surface temperatures, both at the gasket and the diamond anvil, appear to be more pronounced compared with those known for classical external electrical heating. Apart from the tests of the mechanical stability on high-pressure operation in the diamond anvil cell at room temperature, the influence of the anvils in contact with the gasket on the characteristic power–temperature curves, temperature gradients and thermal equilibration resulting from changes in electrical power settings have been evaluated within the scope of a series of experimental investigations. 相似文献
103.
M. Hinczewski A. N. Berker 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(4):461-472
The anisotropic d=3 tJ model is studied by
renormalization-group theory, yielding the evolution of the system
as interplane coupling is varied from the isotropic
three-dimensional to quasi-two-dimensional regimes.
Finite-temperature phase diagrams, chemical potential shifts, and
in-plane and interplane kinetic energies and antiferromagnetic
correlations are calculated for the entire range of electron
densities. We find that the novel τ phase, seen in earlier
studies of the isotropic d=3 tJ model, persists even for
strong anisotropy. While the τ phase appears at low
temperatures at 30–35% hole doping away from 〈
ni〉=1, at smaller hole dopings we see a complex lamellar
structure of antiferromagnetic and disordered regions, with a
suppressed chemical potential shift, a possible marker of
incommensurate ordering in the form of microscopic stripes. An
investigation of the renormalization-group flows for the isotropic
two-dimensional tJ model also shows a clear pre-signature of the
τ phase, which in fact appears with finite transition
temperatures upon addition of the smallest interplane coupling. 相似文献
104.
Akito Kobayashi Yoshiaki
no Tamifusa Matsuura Yoshihiro Kuroda 《Physica C: Superconductivity and its Applications》1998,300(3-4):287-300
Dynamical spin susceptibility χs(q,ω) of the d–p model in the over doping region is investigated by using the auxiliary boson technique. It includes higher order terms of the 1/N-expansion within the random phase approximation (RPA) of the local vertex, where frequency dependence of the quasi-particle interaction is taken into account. The incommensurate spin fluctuation is obtained due to the nesting effect in the low energy region (ωω*), whereas the commensurate one in the high energy region (ωω*), the characteristic energy ω* is estimated to be about 30 meV. Both of the spin–lattice relaxation rate 1/T1 and the spin–spin relaxation rate 1/Tg monotonically increase as T decreases, while the spin Knight shift K is almost independent of T. 相似文献
105.
V. Gasumyants N. Ageev E. Vladimirskaya V. Kaydanov 《Superlattices and Microstructures》1998,24(6):443-447
We report experimental data on the temperature and concentration dependences of the Nernst coefficient in the normal state for the YBa2Cu3 − xCoxOyceramic samples with increasing Co content up tox = 0.3. The Nernst coefficient is positive, and its value increases almost linearly withx. The temperature dependences ofQhave been analyzed on the basis of a narrow band model, together with data on other transport coefficients. Using a complex quantitative analysis of four transport coefficients, we were able to estimate the carrier mobility and to elucidate a character of the energy dependence of the relaxation time. 相似文献
106.
A. Butera M. Vsquez Mansilla A. Fainstein G. V. M. Williams 《Physica B: Condensed Matter》2002,320(1-4):316-318
We have made high-temperature (250 K<T<800 K) DC susceptibility measurements in the compounds RuSr2Eu2−xCexCu2O10 for x=0.6,0.8, and 1.0 in order to determine the Ru effective magnetic moment. After carefully subtracting all contributions to the magnetic susceptibility except that of the Ru ions, we have been able to fit the Ru susceptibility with a law χRu=χ0+CRu/(T−ΘRu). We have found that the Ru effective moment
falls between the values expected for Ru5+ in spin states
and
. We have also found a dependence of μeff(Ru) and ΘRu with the Ce content x. 相似文献
107.
文章简要介绍了高温超导体中的相分离现象及其研究现状,同时报道了作者对La2CuO4体系中的相分离及电荷有序现象的研究工作. 相似文献
108.
J. L. Jorda 《Journal of Thermal Analysis and Calorimetry》1997,48(3):585-596
With the discovery of high temperature superconductivity an extraordinary field for investigations on new materials containing up to (more than) 8 or 9 components has been open. But, in addition to problems specifically related to superconductivity, we are faced with a prelimary difficulty: the preparation of well defined compounds which may have reproducible properties. This difficulty is smoothed out when the phase relations in the relevant systems are known. Differential Thermal Analysis (DTA) contributes to their establishment. However, in multicomponent systems, an isopletic line is expected to intercept various boundary surfaces and the analysis is obviously complicated, compared to low order systems. In addition, by the nature of high temperature superconductors the oxygen partial pressure used for their preparation is an important thermodynamic parameter which contributes to fix the oxygen content in the solid state. During heat treatments, the composition of the systems may change, due to oxygen or volatile oxides (Tl2O3, PbO2 or HgO) release. A permanent composition control then requires thermogravimetric (TG) measurements associated to DTA.This paper attempts to demonstrate the efficiency of the assembly DTA/TG for the study of high temperature superconductors. Going beyond the frame of preparation and quality control, the system is also particularly useful for kinetic studies. Examples will be principally in the (Tl,Pb)-(Ba,Sr)-Ca-Cu-O systems.It is a pleasure to associate to this lecture my colleagues from research groups with which I collaborate from many years in the difficult field of elaboration and characterization of thalliumbased HTSC: T. K. Jondo, K. Lebbou. R. Abraham and M. T. Cohen-Adad in Lyon (Lab. PCM2), M. Couach and A. F. Khoder at the CEN in Grenoble (SPSMS), J. Muller and R. Flukiger at the DPMC in Geneva and of course C. Opagiste and Ph. Galez at the LSM in Annecy. 相似文献
109.
The application of a Fourier spectrometer to the study of the electronic structure in the far infrared of some intermediate valence or heavy fermion materials or of highT
c
superconductors showed that FT-reflectivity is a powerful tool of investigation at very low energies. A very careful control of the experimental conditions and of the reference measurements is necessary to eliminate spurious reflectivities.The results show optical transitions at very low energy and permit to evaluate the electronic structures and the effective mass of the carriers in the vicinity of the Fermi level. 相似文献
110.
Muller and coworkers have introduced the concept of a superconducting glass to explain some magnetization data in highT
csuperconductors. We explain this data using conventional ideas of type-II superconductivity. 相似文献