Determination of $I$– $V$ Curves of HTS Tapes From the Frequency-Dependent AC Transport Loss

The current-voltage characteristics of superconductors are commonly determined by means of a standard four-probe dc measurement technique. In coated conductors, however, one often encounters problems due to weak or no stabilization, and in such a case, when the risk of burning the tape is high, the four-probe approach can fail. In other cases such as in HTS cable structures, in addition to vulnerability and high risk of damage, it may be also difficult to achieve a high critical current level with a power supply that is normally used to characterize single strands. In this paper, we investigated an alternative method to determine the dc I-V curve, based on measuring the ac transport loss as a function of frequency in overcritical current range. AC loss measurements at different frequencies are related to different electric fields in dc, and a curve similar to the dc I-V is obtained. In the experiment, we used a 4-mm-wide YBCO reference tape with 20 μm of Cu stabilization. For the comparison with ac transport loss, the sample was measured with the standard four-probe technique and remained stable even in overload condition.