Scanning SQUID susceptometry of a paramagnetic superconductor
Scanning SQUID susceptometry of a paramagnetic superconductor
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DOI：
10.1103/physrevb.85.224518
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发表时间：
2012-06-15
影响因子：
3.7
通讯作者：
Moler, K. A.
中科院分区：
文献类型：
--
作者：
Kirtley, J. R.;Kalisky, B.;Moler, K. A.
扫描 SQUID 磁化率仪可对样品的局部磁化强度和磁化率进行成像。通过对 SQUID 信号进行精确建模，我们可以确定超导样品的物理特性，例如穿透深度和磁导率。我们计算了非超导基底上具有各向同性伦敦穿透深度 lambda 的任意厚度超导板的扫描 SQUID 电纳测量信号，其中板和基底都可以具有在所施加的场中呈线性的顺磁响应。我们在许多限制下得出了一般表达式的分析近似值。利用我们的结果，我们将实验磁化率数据拟合为三个样品的样品-传感器间距的函数：（1）δ掺杂的SrTiO3，其主要具有抗磁响应，（2）LaNiO3薄膜，其主要具有顺磁响应，以及（3）SrTiO3/LaAlO3界面处的二维电子层，其表现出两种类型的响应。这些公式将允许通过扫描 SQUID 磁化率测量的拟合来确定顺磁自旋和超导载流子的浓度。
Scanning SQUID susceptometry images the local magnetization and susceptibility of a sample. By accurately modeling the SQUID signal we can determine physical properties such as the penetration depth and permeability of superconducting samples. We calculate the scanning SQUID susceptometry signal for a superconducting slab of arbitrary thickness with isotropic London penetration depth lambda on a nonsuperconducting substrate, where both slab and substrate can have a paramagnetic response that is linear in the applied field. We derive analytical approximations to our general expression in a number of limits. Using our results, we fit experimental susceptibility data as a function of the sample-sensor spacing for three samples: (1) delta-doped SrTiO3, which has a predominantly diamagnetic response, (2) a thin film of LaNiO3, which has a predominantly paramagnetic response, and (3) the two-dimensional electron layer at a SrTiO3/LaAlO3 interface, which exhibits both types of response. These formulas will allow the determination of the concentrations of paramagnetic spins and superconducting carriers from fits to scanning SQUID susceptibility measurements.