共查询到17条相似文献,搜索用时 740 毫秒
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本文探讨非晶态超导体的Tc与原子质量M之间的关系,发现在具有相同价电子数的同族元素中,超导Tc与原子质量的立方根成反比,即Tc∝l/M1/3。讨论了晶态超导体的Tc问题,其中包括高Tc氧化物超导体。
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作者在μ*=0情形,从Eliashberg方程解析地导出如下的Tc公式:Tc=αωlogexp{-b((1+cλ)/λ)},式中α=2γ/π,b=c=1;Inγ=C=0.5772是Euler常数。这个Tc公式只有在Tc=0.36/α(k)以下才是正确的,α是个大于1并随材料而异的常数。我们推测,当Tc超过上述范围后,Tc公式的函数结构很可能不同于McMillan Tc公式,至少α,b和c等参量不再是些不依赖于材料的常数了。
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采用第一性原理计算方法,研究了三元氢化物Y-Si-H体系在高压下的晶体结构、电子性质及超导性质,发现了热力学稳定的YSiH7、YSiH9、YSi2H12和YSiH18,以及热力学亚稳的YSi2H13、YSi2H14和Y2SiH17。电子性质计算表明,YSiH7为绝缘体,YSi2H13为半导体,其余氢化物均具有金属特性。通过麦克米兰方程估算超导转变温度(Tc)发现,YSi2H12具有最高的Tc,在100 GPa下为43.5 K。YSi2H14的动力学稳定压力可降至40 GPa,Tc为23.8 K,是Y-Si二元化合物中最高Tc的2倍,... 相似文献
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本文研究了C-15结构化合物(Zr0.5Hf0.5-xTax)V2(x≤0.2)和(Hf0.5Zr0.5-xNbx)V2(x≤0.2)的超导转变温度Tc及其压力效应?Tc/?P。报道了实验方法与结果。与(Hf1-xTax)V2和(Zr1-xTax)V2的情况不同,在(Zr0.5Hf0.5-xTax)V2中Ta的引入使常压下的Tc下降,然而(?)Tc/(?)P却大为提高。因此高压下Zr0.5Hf0.45Ta0.05V2的Tc反而比Hf0.5Zr0.5V2更高。导出了一个基于角动量分波表象能带论方法的描述压力效应的新关系式。它指出导带电子波函数中的高角动量成分变化对Tc的压力效应影响比较重要。这个公式有助于理解上述复杂的实验现象,并能合理地解释某些元素(如Cs,Ba,La等)的Tc随压力剧增的事实。
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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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采用Green函数技术,我们讨论了温度从T=0直到T=Tc范围内铁磁体表面和界面的磁化强度随温度的变化情况,所得到表面磁化强度的结果与其他作者的结果一致;而在界面计算中,我们发现界面的Tc与体内的不同,并且找到了一个关系式:TccA,TcB)。
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根据文献[1]中给出的模型和能隙方程,计算了超导态的热力学临界磁场,Tc处的比热跃变以及Tc以下的比热行为。结果表明:有关热力学量的临界值与实验结果定性相符;Tc以下的比热行为在整个温区与CeCu2Si2和UBe13的实验结果符合。
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Entanglement teleportation via two spins coupled to each other by one axis twisting spin squeezing interaction is investigated. We mainly concentrate on the properties of the channel entanglement, the output entanglement and the teleportation fidelity. It shows that the output entanglement increases linearly with increasing the value of the input entanglement. With the increasing of T, the teleportated entanglement increases sharply from zero to a maximum value and then decreases slowly to zero when the temperature is improved to one threshold value of T c , and the threshold value of T c increases with the increasing of the input entanglement. When enlarging the external magnetic, F a firstly decreases quickly to a minimum value as the critical magnetic field Ω c is reached, then it increases abruptly to a maximum value and finally it will be a certain value. Besides, the critical external magnetic Ω c increases when μ is larger. For Ω<Ω c the value of the average fidelity increases with the increasing of μ, but for Ω>Ω c the value of it decreases from a maximum value. The influence of T on the average fidelity is similar with μ. 相似文献
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Using the Landau theory of phase transitions it has been shown that for a second order phase transition Ω/kBTc ? 0.01. and its isomorphs 4Ω/J1 ? 1 and for a first order transition Ω/kBTc ? 0.01. 相似文献
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A. A. Kozhevnikov 《JETP Letters》2000,72(12):608-611
The problem of explaining the critical angular velocity Ωc when the formation of a vortex in the stirred Bose-Einstein condensate becomes energetically possible is considered in the framework of the variational approach. The origin of smallness of the calculated Ωc in comparison with the measured values, which takes place for a pure quantum state with the unit angular momentum per condensed particle, is uncovered. The agreement with the measured Ωc is achieved upon admitting a small admixture of the zero angular-momentum state in the wave function of the one-vortex quantum state prepared after stirring. A portion of this admixture amounts to 1–13% of the total condensed atoms. A possible test of this hypothesis is proposed. 相似文献
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Using general methods developed in a previous treatment we study correlations in inhomogeneous Ising models on a square lattice. The nearest neighbour couplings can vary both in strength and sign such that the coupling distribution is translationally invariant in diagonal direction. We calculate correlations parallel to the layering in the diagonally layered model with periodv=2, the so-called “general square lattice” model (GS). If the model has a finite critical temperature,T c>0, we have a spontaneous magnetization belowT c vanishing atT c with the Ising exponent β=1/8. AtT c correlations decay algebraically with critical exponnet η=1/4 and exponentially forT>T c. In the frustrated case we have oscillatory behaviour superposed on the exponential decay where the wavevector of the oscillations changes at some “disorder temperature”T D(>T c) from commensurate to temperature-dependent in commensurate periods. If the critical temperature vanishes,T c=0 we always have exponential decay at finite temperatures, while atT=T c=0 we encounter either long-range order or algebraic decay with critical index η=1/2, i.e.T=0 is thus a critical point. 相似文献