Flux Creep in Hard Superconductors
Flux Creep in Hard Superconductors
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硬超导体中的磁通蠕变
DOI：
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发表时间：
1963
期刊：
影响因子：
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通讯作者：
A. Strnad
中科院分区：
文献类型：
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作者：
Y. B. Kim;C. F. Hempstead;A. Strnad
用管子磁化和电阻测量研究了硬超导体的阻态。Anderson的磁通蠕变理论很好地解释了本文所报道的实验观测结果。在输运电流密度J和垂直于J的磁场B的存在下，观察到了电阻现象。结果表明，整个阻态谱可以用单个参数$ensureath{α}=J(B+{B}_{0})$来表示，其中${B}_{0}$是材料的常数。该参数实质上表示材料中的洛伦兹力或磁压梯度。虽然在很大范围内保证数学{α}$的值是可能的，但在给定的实验条件下，超导电性通常不能保持在临界值以上。在管状磁化中，临界值${EnsureMath{Alpha}}_{c}$主要由持续电流$J$衰减的速率决定。如果$Ensureath{Alpha}$上升到超过${Ensureath{Alpha}_{c}$，则$J$迅速衰减，$Ensureath{Alpha}$迅速下降到接近${Ensureath{Alpha}}_{c}$。继续缓慢减少，但与理论预测的时间的对数成正比。用该理论解释了观测到的温度依赖关系。通过放置在超导管附近的拾取线圈，可以检测到由磁通束运动所预期的离散的、随机的磁场变化。在电阻测量中，通过在存在垂直场的情况下向外部提供$J$来测量3Nb-Zr线材样品上出现的电压。观察到的电压被解释为磁通蠕变引起的未补偿电动势的表现。在给定温度下，在$J$和$H$的大范围内获得的电压读数仅是$EnsureMath{Alpha}=J(H+{B}_{0})$的函数。$V(EnsureMath{Alpha}，T)$定性地遵循理论所期望的形式。在电阻测量中，临界值${Ensureath{Alpha}}_{p}$由材料中的功率消耗决定。如果$EnsureMath{Alpha}$升高超过${EnsureMath{Alpha}}_{p}$，则热传导滞后于功率耗散，并且样本经历到正常状态的灾难性转变。
Resistive states of hard superconductors have been investigated by tube magnetization and resistance measurements. The flux-creep theory of Anderson is very effective in accounting for the experimental observations reported herein. Resistive phenomena were observed in the presence of transport current density $J$ and magnetic field $B$ perpendicular to $J$. It is found that the whole spectrum of resistive states can be represented in terms of a single parameter $ensuremath{alpha}=J(B+{B}_{0})$, where ${B}_{0}$ is a constant of the material. This parameter represents essentially the Lorentz force or the magnetic pressure gradient in the material. While a wide range of $ensuremath{alpha}$ values is possible, under given experimental conditions superconductivity usually can not be maintained above a critical value. In tube magnetization, the critical value ${ensuremath{alpha}}_{c}$ is determined primarily by the rate with which the persistent current $J$ decays. If $ensuremath{alpha}$ is raised beyond ${ensuremath{alpha}}_{c}$, $J$ decays rapidly and $ensuremath{alpha}$ quickly falls near to ${ensuremath{alpha}}_{c}$. $ensuremath{alpha}$ continues to decrease slowly, but proportional to the logarithm of time as predicted by the theory. The observed temperature dependence of ${ensuremath{alpha}}_{c}$ is accounted for by the theory. Discrete, stochastic changes in field anticipated from the motion of flux bundles have been detected through pickup coils placed in close proximity to the superconducting tube. In resistance measurements, voltages appearing across 3Nb-Zr wire samples were measured by supplying $J$ externally in the presence of a perpendicular field $H$. The voltage observed is interpreted as a manifestation of an uncompensated emf arising from flux creep. At a given temperature, voltage readings obtained over a wide range of $J$ and $H$ are found to be a function of $ensuremath{alpha}=J(H+{B}_{0})$ only. $V(ensuremath{alpha}, T)$ follows qualitatively a form expected from the theory. In resistance measurements, the critical value ${ensuremath{alpha}}_{p}$ is determined by the power dissipation in the material. If $ensuremath{alpha}$ is raised beyond ${ensuremath{alpha}}_{p}$, thermal conduction lags the power dissipation and the sample undergoes a catastrophic transition to the normal state.