Scaling Law on the temperature and magnetic field dependence of critical current density in the mixed state of superconductors

1.利用我们提出的推广的玻璃-液体相变理论，在假设在G-L相变附近E对J的标度律可近似应用到相当低的温度下，导出了高温铜酸盐超导体中电场E=E_c时观察到的临界电流密度J_c与温度T和磁通密度B的关系的理论表达式。结果表明，高温铜酸盐超导体中J_c的T和B依赖关系的标度律表达式与金属超导体中J_c的标度律明显不同。通过输运测量，研究了PLD法制备的YBa2Cu3O7薄膜中柱状缺陷密度对钉扎参数的影响。为了以可控的方式人为地产生缺陷，重离子被照射到薄膜上。临界电流密度J_c i…由于样品中引入了较强的钉扎点，随着辐照剂量的增加，更多的样品增加。这些结果可以用渗流模型描述为诱导缺陷对钉扎强度分布的影响。采用PLD法制备了含BaZrO_3(BZO)纳米棒的ErBa2Cu3Oy(ErBCO)薄膜，提高了临界电流密度J_c，结果表明，在磁场中，含1.5wt%BZO(Er15)的ErBCO薄膜的临界电流密度高于含0.5wt%BZO(Er05)的ErBCO薄膜。当磁场平行于c轴时，在两种薄膜中都观察到了J_c随角度的变化而出现的峰值。结果表明，该峰是由平行于c轴取向的BZO纳米棒的磁通钉扎作用引起的。在磁场依赖关系中观察到钉扎参数的峰值。这一事实可能是由于BZO纳米棒的密度与熔剂的密度相匹配，这一点得到了透射电子显微镜的证实。较少

1. A theoretical expression for the dependences on the temperature, T, and the flux density, B, of the critical current density, J_c, observed at the value of the electric field E=E_c in the high temperature cuprate superconductors was derived by using a generalized theory of the Glass-Liquid Transition proposed by us, under the assumption that the scaling law of E against J near the G-L Transition can be approximately applied down to fairly low temperatures. It is shown that the derived expression for the scaling law for the T and B dependences of J_c in the high temperature cuprate superconductors is noticeably different from that for the metallic superconductors.2. We have studied the effect of the densities of columnar defects on pinning parameters in YBa_2Cu_3O_7 thin films prepared by the PLD method with the transport measurements. In order to produce the defects artificially in a controlled manner, the heavy-ions were irradiated onto the films. The critical current density J_c i … More ncreases with the doses of the irradiation due to the introduction of the strong pinning sites into samples. These results could be described by the percolation model as a variation of pinning strength distribution affected from the induced defects.3. ErBa_2Cu_3O_y (ErBCO) thin films with BaZrO_3(BZO) nano-rods were prepared by a PLD method for an enhancement of critical current density J_c. The values of J_c for the ErBCO thin film containing 1.5wt% BZO (Er15) in magnetic fields are higher than those for the ErBCO thin film containing 0.5wt% BZO (Er05). The peaks of J_c have been observed in the angular dependence of J_c in both the films when the magnetic field is applied parallel to the c-axis. It has been found that the peak is attributed to the flux pinning by BZO nano-rods oriented parallel to the c-axis. The peak of the pinning parameter has been observed in the magnetic field dependence. This fact is probably due to the matching the density of BZO nano-rods with that of fluxoids, which was confirmed by TEM observations. Less