Microscopic mechanism to determine strain dependence of critical current for Yttrium-based high Tc superconducting film

Y基超导膜表现出应变对临界电流的可逆效应。然而，这一现象的起源尚不清楚。在本研究中，我们用四点弯曲法成功地研究了在SrTiO_3单晶衬底上生长的无晶界YBCO薄膜的磁场临界电流与应变的关系。结果表明，对于与实际双轴织构多晶膜相似的单晶膜，在某一外加应变下的临界电流峰值是确定的。这表明晶内的晶格形变有助于应变对临界电流和晶界应变的可逆影响。此外，利用基于X射线衍射技术的同步辐射技术，直接研究了不同应变敏感性的Gd基超导薄膜在拉伸载荷下沿a、b轴方向的内部应变变化。实验表明，应变灵敏度较小的GdBCO薄膜沿[110]方向平行于加载轴方向，a轴和b轴方向的感生应变小于a轴和b轴取向于导体轴线和宽度的薄膜。结果表明，超导薄膜晶体取向的差异可能是决定临界电流应变依赖性的微观原因之一。

Yttrium-based superconducting film exhibits reversible effect of strain on critical current. However, the origin of this phenomenon has not been clarified. In this study, we succeeded in evaluating strain dependence of critical current in magnetic field for YBCO film without grain boundaries grown on SrTiO_3 single crystal substrate by means of a 4-point bending method. As a result, the peak of the critical current at a certain applied strain was confirmed for a single-crystalline film similar with the practical biaxially-textured polycrystalline film. This suggests that lattice deformation within a grain contributes to the reversible effect of strain on critical current as well as strain at the grain boundaries. In addition, change in internal strain under tensile loading was directly evaluated along a-anb b-axes for Gd-based superconducting films with different strain sensitivity to critical current using synchrotron radiation based on X-ray diffraction technique. This experiment reveals that GdBCO film with small strain sensitivity orients its[110] direction parallel to the loading axis and induced strain along the a-and b-axes is smaller than the other film in which a-and b-axis orients to the conductor axis and width. As a result, it was clarified that difference in crystal orientation of superconducting film can be one of the microscopic origins to determine strain dependence of critical current.