Superconductors in a temperature gradient
Superconductors in a temperature gradient
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温度梯度下的超导体
DOI：
10.1088/0953-2048/8/4/001
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发表时间：
1995
影响因子：
3.6
通讯作者：
R. Huebener
中科院分区：
文献类型：
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作者：
R. Huebener
在第二类超导体的混合状态下，准粒子和磁通量量子通过热扩散对温度梯度做出响应，以这种方式分别产生塞贝克和能斯特效应。我们对塞贝克效应的理解起源于两种流体逆流概念的延伸，最初由金兹伯格引入，到涡旋（具有正常核心）嵌入超导相的情况。这一机制的结果之间的紧密联系塞贝克系数和电阻率由于涡流运动。在所有的热扩散过程中，它是决定驱动力的扩散物种的运输熵，并说明了这个量的物理。我们的讨论的实验方面集中在最近的工作与铜酸盐超导体。在混合状态下的电阻转变的特征加宽，发现在这些材料中，由于它们的高各向异性和特殊的涡旋结构（煎饼涡旋），结果在一个类似的扩大的温度范围内的塞贝克和能斯特效应出现。在铜氧化物超导体中，由于这些材料的大的各向异性、小的相干长度和高的临界温度，涨落效应非常显著。在这里，能斯特效应产生特别有用的信息，因为它在正常状态下几乎消失，并且不需要复杂的减法程序。与所有输运现象一样，霍尔角也出现在热扩散过程中，并给出了总结性的讨论。观察到的异常大的霍尔角的热扩散的旋涡仍然是令人费解的。一个尝试性的解释是基于未绑定的涡-antivortex对的热生成。
In the mixed state of a type II superconductor quasiparticles and magnetic flux quanta respond to a temperature gradient by thermal diffusion, in this way generating the Seebeck and Nernst effects, respectively. Our understanding of the Seebeck effect originates from an extension of the two-fluid counterflow concept, originally introduced by Ginzburg, to the situation where vortices (with a normal core) are imbedded in the superconducting phase. This mechanism results in an intimate connection between the Seebeck coefficient and the electric resistivity due to vortex motion. In all thermal diffusion processes it is the transport entropy of the diffusing species that determines the driving force, and the physics of this quantity is illustrated. Our discussion of the experimental side concentrates on the recent work performed with the cuprate superconductors. The characteristic broadening of the resistive transition in the mixed state, found in these materials due to their high anisotropy and the peculiar vortex structure (pancake vortices), results in a similar broadening of the temperature regime where the Seebeck and Nernst effects appear. In the cuprate superconductors fluctuation effects are highly pronounced because of the large anisotropy, small coherence length, and high critical temperature of these materials. Here the Nernst effect yields particularly useful information since it nearly vanishes in the normal state, and complicated subtraction procedures are unnecessary. As in all transport phenomena, the Hall angle also appears in the thermal diffusion processes, and a summarizing discussion is given. The observation of an unusually large Hall angle for the thermal diffusion of vortices still remains puzzling. A tentative explanation is based on the thermal generation of unbound vortex-antivortex pairs.