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在本文中,根据超导材料组成的结构特征,以电声子机制为基础,研究了在超导材料中超导部分(导电层部分)1-ω与非超导部分(载流子库部分)ω对超导材料的超导转变温度Tc的影响具有本质上的不同,提出了在超导材料中,ω部分通过转移电荷增加1-ω部分的N(O)部分、强化θ促使Tc增加. 相似文献
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葛雨 《原子与分子物理学报》2020,37(2):231-238
使用第一性原理方法,研究了拓扑材料MoP在高压下的电子结构和晶格动力学行为.高压下MoP的晶体结构和费米面附近的电子能带相对稳定,但是声子能谱以及电声子耦合参数随着压强的增大有明显的变化.声子谱中高频光学支逐渐硬化,低频声学支中也有部分出现明显软化,体系的电声子耦合随压强的增大而逐步变强,导致超导转变温度从常压下的零提高到30 GPa时的0.16 K,最后在50 GPa时提高到1.21 K,与实验的变化趋势基本一致.研究揭示了高压下MoP中出现的超导现象主要是电声子耦合造成的,为理解实验观测到的拓扑超导共存现象提供了一定的理论支持. 相似文献
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BCS超导电性微观理论中提出超导材料的超导转变温度Tc由θ(临近费米界面电子之间的相互吸引),λeff=N(O)V(N(O)在费米界面每单位能量的一种自旋Bloch态密度;V=平均,电子对在-ω<ε<ω在区域中跃迁的矩阵元Vkk′能为衡量的平均矩阵元)决定,并给出计算公式.基于高Tc超导材料的特征,用电负性均衡原理分析了由于在高Tc超导材料中的元素有化学键的形成,N(O)和V具有特殊的变化,电声子机制可以产生高Tc超导电性。 相似文献
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基于小型低温制冷机的高温超导材料超导转变温度测量装置 总被引:1,自引:0,他引:1
高温超导材料的超导转变温度是判断超导材料性能优劣的一个重要指标,而超导材料转变温度的测量一般采用输运方法进行电阻随温度变化来确定.本文介绍一种新近研制的基于低温制冷机的高温超导材料超导转变温度测量装置,能有效的将样品温度从室温连续均匀的降至35K,通过Lab VIEW编写的数据采集系统人机界面,采用电流换向技术消除热电势,可以准确测量出超导材料的超导转变温度.经实验验证,该测量装置测量精确和重复性良好,可作为有效判定高温超导材料性能优劣的一种手段. 相似文献
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综述了近几年来C60超导体,特别是K3C60和Rb3C60单昌超导体的实验研究结果,主要包括超导转变温度以上的电阻-温度关系、高温下电阻的饱和现象及超导转变温度、上临界磁场和相干长度等超导性质。上述实验结果可以用传统的电子-声子相互作用理论来解释。 相似文献
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氮化铌(NbN) 低温超导薄膜是用于制作超导器件的典型材料. 基于 NbN 超导薄膜的超导纳米线单光子探测器(SNSPD) 在量子通信、 暗物质探测、 激光测距等领域都有着广泛应用. 本工作借助中国科学院兰州近代物理所320 kV 低能重离子综合研究平台采用300-keV H1 + 离子对7 nm 厚度的低温超导材料 NbN 超薄膜进行了离子辐照, 得到了辐照前后超导转变温度Tc 及超导能隙 Δ(0) 、 费米面附近电子态密度 N0 等其他材料参数的变化, 为借助离子辐照手段改善 NbN SNSPD 性能提供了实验参考. 相似文献
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《中国物理 B》2021,30(7):76301-076301
Based on density functional first-principles calculations and anisotropic Eliashberg equations, we have investigated the electronic structure, lattice dynamics, and phonon-mediated superconductivity in newly synthesized layered compound Sr BC under pressure. Different from Li BC and Mg B2, our calculations surprisingly reveal that Sr BC is isotropic in compressibility, due to the accumulation of substantial electrons in the interstitial region. We find that the Sr phonons strongly couple with B-2 pz orbital and the interstitial states, giving rise to a two-gap superconductivity in Sr BC, whose transition temperature shows an inverted V-shaped dependence on pressure. The maximal transition temperature is about 22 K at50 GPa. On both sides of 50 GPa, the transition temperature exhibits quasi-linear variation with positive and negative slopes, respectively. Such a variation of transition temperature is infrequent among phonon-mediated superconductors. The competition between enhanced electron–phonon matrix element and hardened phonons plays an essential role in governing the behavior of the critical temperature. 相似文献
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In the conventional superconductors, the Cooper pairs are mediated by phonons, which is a process where only the correlations between the phonons and the charge properties of the electrons are needed. However, superconductivity can also be derived from other types of elementary excitations. The spin fluctuations are arguably the most promising candidate that can mediate such unconventional superconductivity. In some of the important systems such as cuprates, Fe-based superconductors and heavy-fermion superconductors, spin fluctuations play a key role in the mechanism of their superconductivity although there are still many debates. In this paper, we will give a brief review on the correlation between the spin fluctuations and superconductivity. 相似文献
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Mazin II 《Physical review letters》2005,95(22):227001
Recently discovered superconductivity in YbC6 and CaC6, at temperatures substantially higher than previously known for intercalated graphites, raises several new questions. (1) Is the mechanism considerably different from that of previously known intercalated graphites? (2) If superconductivity is conventional, what are the relevant phonons? (3) Given the extreme similarity between YbC6 and CaC6, why are their critical temperatures so different? We address these questions on the basis of first-principles calculations and conclude that coupling with intercalant phonons is likely to be the main force for superconductivity in YbC6 and CaC6, but not in alkaline-intercalated compounds, and explain the difference in T(c) by the "isotope effect" due to the difference in Yb and Ca atomic masses. 相似文献
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V. A. Moskalenko P. Entel M. Marinaro D. F. Digor 《Journal of Experimental and Theoretical Physics》2003,97(3):632-644
The interaction of strongly correlated electrons with phonons in the framework of the Hubbard-Holstein model is investigated. The electron-phonon interaction is considered to be strong and is an important parameter of the model, in addition to the Coulomb repulsion of electrons and the band filling. This interaction with nondispersive optical phonons is transformed to the problem of mobile polarons using the canonical transformation of Lang and Firsov. We discuss the case where the on-site Coulomb repulsion is exactly canceled by the phonon-mediated attractive interaction. It is suggested that polarons exchanging phonon clouds can lead to polaron pairing and superconductivity. The fact that the frequency of the collective mode of phonon clouds is larger than the bare frequency then determines the superconducting transition temperature. 相似文献
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Recent investigations of superconductivity in carbon nanotubes have shown that a single-wall zig-zag nanotube can become superconducting at around 15?K. Theoretical studies of superconductivity in nanotubes using the traditional phonon exchange model, however, give a superconducting transition temperature T c less than 1?K. To explain the observed higher critical temperature we explore the possibility of the plasmon exchange mechanism for superconductivity in nanotubes. We first calculate the effective interaction between electrons in a nanotube mediated by plasmon exchange and show that this interaction can become attractive. Using this attractive interaction in the modified Eliashberg theory for strong coupling superconductors, we then calculate the critical temperature T c in a single-wall nanotube. Our theoretical results can explain the observed T c in a single-wall nanotube. In particular, we find that T c is sensitively dependent on the dielectric constant of the medium, the effective mass of the electrons and the radius of the nanotube. We then consider superconductivity in a bundle of single-wall nanotubes and find that bundling of nanotubes does not change the critical temperature significantly. Going beyond carbon nanotubes we show that in a metallic hollow nanowire T c has some sort of oscillatory behaviour as a function of the surface number density of electrons. 相似文献
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We study the formation of the charge-density wave long-range order in a system of repulsive 1D electrons coupled to 3D phonons. We show that the charge-density wave can be stabilized by interaction with phonons in quasi-1D crystals and semiconducting nanowires. In the case of metallic atomic chains, interaction with phonons of a 3D substrate is not enough, and violation of the translational invariance by commensurable perturbation or disorder is needed. The possibility of stabilization of superconductivity in 1D electrons with attraction by means of tunnel coupling to a 3D metal is considered. 相似文献
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Ohgushi K Yamamoto A Kiuchi Y Ganguli C Matsubayashi K Uwatoko Y Takagi H 《Physical review letters》2011,106(1):017001
We have successfully synthesized a new rhenium-based hexagonal bronze material, HgxReO3, which exhibits superconductivity with the transition temperature Tc=7.7 K at ambient pressure and 11.1 K at 4 GPa. This compound is a superconductor with the highest Tc among hexagonal bronzes. Moreover, it presents the novel crystallographic feature that (Hg2)2+ polycations, in contrast to monatomic cations in known hexagonal bronzes, are incorporated into open channels. There is evidence that conducting electrons tightly couple with Hg-related phonons. Our results inspire detailed studies on the role of the rattling phonon in the occurrence of superconductivity in the hexagonal bronzes. 相似文献
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Christopher Homes 《Synchrotron Radiation News》2013,26(3):9-14
Superconductivity refers to a fascinating state of matter where the electrical resistivity is precisely zero. Originally discovered in elemental metals such as mercury and tin in the early part of the last century, the mechanism of superconductivity was elusive and nearly 50 years passed before a comprehensive theory for superconductivity in metals was proposed by Bardeen, Cooper and Schrieffer [1] (the “BCS” theory). In a normal metal, the resistivity is determined by the elastic scattering of carriers. However, when a metal becomes a superconductor, the charge carriers are no longer single electrons, but rather pairs of electrons (“Cooper pairs”), which are bound together by a phonon interaction (phonons are the vibrations of the atomic lattice), and flow without resistance. 相似文献