Offset criterion for determining superconductor critical current

Critical‐current criteria based on electric field or resistivity can present a number of problems in defining critical current, especially for high Tc superconductors in the vicinity of the critical temperature or upper critical field. The resulting critical‐current density Jc can be quite arbitrary, since it depends strongly on criterion level at high fields and temperatures. These Jc definitions also create problems in distinguishing between superconductors and high‐conductivity normal metals such as copper. They can also bias Jc data when superconductors are compared that have different values of normal‐state resistivity. To minimize these problems, an intrinsic Jc criterion is proposed, which effectively separates superconducting and normal‐state properties. Based on the long‐standing concept of a flux‐flow resistivity, Jc is defined as the current where the tangent to the E‐J curve at a given electric field level extrapolates to zero electric field. This determines an offset Jc that minimizes the abo...