Department of Physics, University of Pune, Pune-411007, India.
J Phys Condens Matter. 2010 May 26;22(20):205701. doi: 10.1088/0953-8984/22/20/205701. Epub 2010 Apr 26.
Experiments carried out on the intermetallic superconducting material MgB(2) have shown anomalous magnetic field dependence of upper critical field, small angle neutron scattering form factor, specific heat, critical current etc. Similarly, scanning tunnelling microscopy (STM) experiments on vortex structures have shown unusually large vortex core size and two different magnetic and spatial field scales. Also, whereas the specific heat measurements and isotope shift experiments have shown Bardeen-Cooper-Schrieffer-like (BCS-like) behaviour, the temperature dependences of the penetration depth experiments have shown non-BCS-like behaviour. These anomalous behaviours have been attributed to the multiband superconductivity of this material and the nature of the local spatial behaviour of the magnetic induction and the order parameter components having two length scales. We report an analytical investigation of the effect of two length scales on the temperature and the applied magnetic field dependence of several properties of MgB(2), such as, the penetration depth, single vortex and vortex lattice structure, vortex core radius, reversible magnetization, critical current, small angle neutron scattering form factor and the shear modulus of the vortex lattice within the framework of two-order parameter Ginzburg-Landau theory. We solve the corresponding nonlinear Ginzburg-Landau equations numerically exactly using an iterative method for arbitrary applied field H(c1) < H < H(c2), the Ginzburg-Landau parameter and vortex lattice symmetry. This enables us to compute the local spatial behaviour of the magnetic induction and the order parameters accurately for arbitrary applied field and a wide range of temperature. Comparison of the analytical results with experiments on MgB(2) gives very good agreement.
对金属间超导材料 MgB(2) 的实验表明，上临界场、小角度中子散射形式因子、比热容、临界电流等具有反常的磁场依赖性。类似地，对涡旋结构的扫描隧道显微镜 (STM) 实验表明，涡旋核具有异常大的尺寸和两个不同的磁场和空间尺度。此外，尽管比热容测量和同位素位移实验表明存在 Bardeen-Cooper-Schrieffer 型 (BCS 型) 行为，但穿透深度实验的温度依赖性表现出非 BCS 型行为。这些反常行为归因于这种材料的多带超导性以及磁感应和序参量分量的局部空间行为具有两个长度尺度的性质。我们报告了在双序参量的框架内，对 MgB(2) 的几个性质，如穿透深度、单个涡旋和涡旋晶格结构、涡核半径、可逆磁化率、临界电流、小角度中子散射形式因子和涡旋晶格的剪切模量，对两个长度尺度的温度和外加磁场依赖性的分析研究。我们使用迭代方法，针对任意外加场 H(c1) < H < H(c2)、Ginzburg-Landau 参数和涡旋晶格对称性，对相应的非线性 Ginzburg-Landau 方程进行了精确数值求解。这使我们能够准确计算任意外加场和宽温度范围内的磁感应和序参量的局部空间行为。与 MgB(2) 实验的分析结果进行比较，得到了非常好的一致性。
