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51.
B. Krunavakarn 《Physics letters. A》2019,383(12):1341-1344
We consider a superconducting spin valve in multiply connected superconductor-ferromagnet hybrid geometry such as a superconducting ring enclosed a ferromagnetic metal, in the framework of linearized Usadel equations. We simplify our model by considering the presence of the exchange field in the superconducting ring which allows us to manipulate magnetization orientations in parallel or antiparallel configurations by switching the weaker exchange field. In such geometry the superconducting ground state is activated to higher orbital states characterized by the nonvanishing vorticity parameters L which will be the energetically favorable superconducting state in some ranges of the proximity superconductor-ferromagnet region. The competing effects caused by the exchange interactions and the orbital effect, are analyzed through the nonmonotonic dependence of the superconducting critical temperature on the radius of the ferromagnetic core. The analytic formula is obtained within the single mode approach and the analysis of the spin switch effect is given. 相似文献
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The effect of metal substitution in La2C2Br2 by Lu (non-magnetic) and Ce (magnetic), respectively, on Tc was studied. The Lu substitution affects Tc, which decreases moderately with increasing amount of Lu. However Ce substitution affects Tc drastically, such that only 10% Ce substitution makes superconductivity disappear. 相似文献
55.
Lead (Pb) has been a prototypical system to study diffusion and reconstruction of silicon surfaces. However, there is a discrepancy in literature regarding the critical coverage at which island formation takes place in the Stranski-Krastanov (S-K) mode. We address this issue by studying the initial stages of evolution of the Pb/Si(1 1 1)7 × 7 system by careful experiments in ultra-high vacuum with in situ characterization by auger electron spectroscopy, electron energy loss spectroscopy and low-energy electron diffraction. We have adsorbed Pb onto clean Si(1 1 1 )7 × 7 surface with sub-monolayer control at different flux rates of 0.05 ML/min, 0.14 ML/min and 0.22 ML/min, at room temperature. The results clearly show that the coverage of the Pb adlayer before the onset of 3D Pb islands in the S-K mode depends on the flux rates. LEED results show the persistence of the (7 × 7) substrate reconstruction until the onset of the island formation, while EELS results do not show any intermixing at the interface. This suggests that the flux rates influence the kinetics of growth and the passivation of dangling bonds to result in the observed rate-dependent adlayer coverages. 相似文献
56.
M. Yokoyama I. Kawasaki S. Oinuma N. Oyama K. Tenya H. Amitsuka 《Physica B: Condensed Matter》2009,404(17):2539
We performed the elastic neutron scattering experiments on the mixed compounds CeRh1-xCoxIn5, and found that doping Co into CeRhIn5 dramatically changes the antiferromagnetic (AF) structure. The incommensurate AF state with the propagation vector of observed in pure CeRhIn5 is suppressed with increasing x, and new AF states with an incommensurate and a commensurate modulations simultaneously develop near the AF quantum critical point: xc0.8. These results suggest that the AF correlations with the qc and q1 modulations enhanced in the intermediate Co concentrations may play a crucial role in the evolution of the superconductivity observed above x0.4. 相似文献
57.
D.J. Singh M.-H. Du L. Zhang A. Subedi J. An 《Physica C: Superconductivity and its Applications》2009,469(15-20):886-889
The layered iron superconductors are discussed using electronic structure calculations. The four families of compounds discovered so far, including Fe (Se, Te) have closely related electronic structures. The Fermi surface consists of disconnected hole and electron cylinders and additional hole sections that depend on the specific material. This places the materials in proximity to itinerant magnetism, both due to the high density of states and due to nesting. Comparison of density functional results and experiment provides strong evidence for itinerant spin fluctuations, which are discussed in relation to superconductivity. It is proposed that the intermediate phase between the structural transition and the SDW transition in the oxy-pnictides is a nematic phase. 相似文献
58.
K. Yamaji T. Yanagisawa M. Miyazaki R. Kadono 《Physica C: Superconductivity and its Applications》2009,469(15-20):1037-1040
Naito et al. reported that some non-doped T′-214-type compounds drive high-Tc superconductivity. The compounds are considered to be metallic since on-site Coulomb energy U is moderate and the Fermi surface is much deformed in these compounds. In order to confirm this picture and extract electronic structure information, we have examined the phase diagram of the metallic state of the 2D Hubbard model as a function of U and t′ (with t″ we fixed at − t′/2 here; t′ and t″ are the second- and third-neighbor transfer energies, respectively) by means of the variational Monte–Carlo method. We employed a Jastrow-type Gutzwiller trial wave function. In the studied range of U = 2–12, the boundary value for |t′| at which SDW disappears increases almost linearly with U. Jump-wise transition to the Mott insulator state was not observed. Using the boundary curve and experimental band parameter values, we estimate U 5 for T′-214 compounds. Preceding works are discussed in the last part. 相似文献
59.
G. Srinivas C.A. Howard N.T. Skipper S.M. Bennington M. Ellerby 《Physica C: Superconductivity and its Applications》2009,469(22):2000-2002
The structure and superconducting properties of high temperature hydrogenated calcium-graphite intercalation compound, CaC6 have been investigated using room temperature X-ray diffraction, and temperature and field dependence of magnetisation. It is found that the hydrogenation can only decompose the CaC6 phase, and generate a mixture of CaH2 and graphite as the final compound. The hydrogenation of CaC6 also reveals a degradation of its superconducting properties. The experimental results are discussed in detail and it is found that the formation of stable CaH2 and deintercalation are the main source for observed phase separation and suppression in superconductivity. 相似文献
60.
在广义梯度近似(GGA)和GGA+U的框架下,用第一性原理方法研究了用FeAs单层的简单模型来研究LaFeAsO和BaFe2As2的合理性. 对未掺杂的FeAs单层,优化的几何结构及其对应的电子结构与本体的性质差异较大,并且在单层中没有发现体相中的共线反铁磁基态. 另外,在单层中,As与Fe层之间在z方向的间距随电子和空穴掺杂浓度的变化也与实验结果不符,这些结果表明,在LaFeAsO和BaFe2As2中,FeAs层与其他层之间的相互作用是不可忽略的,用简单的FeAs单层来处理Fe基超导体需要考虑更多的修正 相似文献