共查询到18条相似文献,搜索用时 437 毫秒
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本文用数值解方法从Eliashberg方程计算出超导临界温度Tc,并考察Tc对有效声子谱的依赖关系。在这个研究中,a2F(ω)被取为双δ函数谱,并允许其中的谱参数可以在很宽范围内改变。作者发现在λ<∧区域(即在Tc级数解的收敛圆外),Tc除了依赖λ和矩比外,还依赖Tc级数解的收敛半径倒数Λ;它们之间的关系是有规律的。在这些结果的启示下,本文在μ*=0情形,用弥合数值解的方法得到一个适用于λ<Λ区域的Tc近似公式。接着,本文作者对吉光达和吴杭生的一篇文章进行了研究,指出:该文提出的超导体分类建议及其工作的主要结论是对的。但其中对决定A型超导体临界温度主要参量问题进行的分析,只适用于这样一些A型超导体,它们的收敛半径倒数Λ或者比λ0小,或者虽比λ0大、但λ又小于λ0,其中λ0是个依赖谱形状的参量,它的定义在正文中给出。对另一些A型超导体(λ0<λ<Λ),决定Tc的主要参量不再是λ,而是δ=1/∧0.5(ω1/2/ωlog)5.5λ1.55。
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本文提出一个非晶态非过渡金属超导体的Tc经验公式,Tc=Aλ<ω>1/2/(<ω>/ω0+(1+λ)/20),式中A=(1/5)(K1/2)。计算值和实验值,以及和Garland理论值的比较表明,Tc经验公式能很好地描述非晶态超导体的Tc值。
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本文由超导体强耦合能隙方程出发,对64种有效声子谱求得了近3500个临界温度的数值解。它们说明,在谱面积A不变时,Tc具有条件极值(Tc/A)max。Tc主要取决于α2F(ω)上峰的位置及其面积,与峰的宽度关系不大。控制<ω>及<ω2>两个参量时,用双δ谱来代替L谱所产生的误差为3.2%。本文分析并澄清了文献中关于“λ=2极限”的争论。
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本文中分析了非过渡金属非晶态超导体的超导参量、声子谱参量与霍耳系数之间的经验关系。研究了非晶态超导体的Tc,并得出,声子谱的软化所导致的Tc的提高幅度与电-声子耦合常数λ的提高幅度成线性关系;声子谱的高频截止频率愈高,其Tc也愈高。讨论了利用声子谱的软化虽然能大幅度地提高Tc值,但要获得包括金属Be在内的非过渡金属的高Tc非晶态超导体的希望是渺茫的。还讨论了非晶态超导体的上临界场Hc2和能隙2Δ0所表现出的强耦合效应等问题。
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一、关于提高超导临界温度T_c的问题,最近引起了广泛的兴趣,不少作者从理论上探讨决定T_c的重要材料参数以及T_c的上限问题.吴杭生等将超导体分为两类:A类及B类.两类超导体以文献[4]中给出的T_c级数公式收敛半径Λ为界:当λ<Λ时为A类,T_c主要由电-声子耦合常数λ决定;而当λ>Λ以时,为B类,T_c主要由λ 相似文献
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《Solid State Communications》1987,61(2):101-103
The penetration depths, λ(T), of the heavy-fermion uranium-based superconductors U6X (X = Fe, Co, Mn) have been measured as a function of temperature at ∼ 35 MHz. It was found that the temperature dependence of λ(T) for these compounds agrees well with the BCS theory. However, the values of λ(0) are large. By comparing the Slater-Pauling curve of the X elements with λ(0)-1 for the U6X superconductors, we have found that λ(0)-1 is proportional to the saturation spin moments of elemental X, suggesting that there is a correlation between the superconductivity of these U6X superconductors and the magnetic nature of the X elements. 相似文献
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在大量的非过渡金属和合金中,非晶态超导体的声子谱参数λ,<ω>和<ω2>与霍耳系数R_H之间存在着一个经验关系:在RH=-3.5—-4.0×10-11m3/As之间存在着λ,<ω>和<ω2>的最大值。上述声子谱参数与相应的液态金属的霍耳系数RHL之间也存在着一个和上述类似的经验关系。最后讨论了非晶态超导体的转变温度Tc的提高问题。
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The transition temperature of a superconductor depends on α2 F(ω), the spectral function of the effective interaction due to phonon exchange. We discuss how strongly the transition temperature is influenced by different frequency parts of α2 F(ω). For this purpose the functional derivative δT c /δα2 F(ω) is calculated. It is shown that all frequency regions of α2 F(ω) yield a positive contribution toT c and that the most effective range covers frequencies, slightly above 2πT c . The functional derivative is calculated numerically for several superconductors from their measured α2 F(ω)-spectra. Finally, we discuss the change in transition temperature due to the softening of α2 F(ω) which has been observed in amorphous superconductors. 相似文献
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The present baryon asymmetry of the universe has finally been determined at the finite temperature electroweak phase transition. The strength of this transition plays a crucial role. The effective action is presented to higher orders, including wave function correction factors and the fullg 4, λ2 effective potential. An upper bound for the Higgs massm H~70 GeV is concluded for the reliability of the perturbative approach. The finite temperature electroweak, phase transition is studied on the lattice and the most important results of Monte-Carlo simulations are collected. 相似文献