2001/03/07 by Kijoon H. P. Kim, Kim, Kijoon H. P., W. N. Kang +13
Materials Science · Physics and Astronomy · #FOS: Physical sciences #Iron-based superconductors research #Materials Science (cond-mat.mtrl-sci) #Physics of Superconductivity and Magnetism #Superconductivity (cond-mat.supr-con) #Superconductivity in MgB2 and Alloys
paper · pdf · doi:10.48550/arxiv.cond-mat/0103176
openalex publication_date 2001/03/07 · openalex created_date 2022/09/30 · openalex updated_date 2026/07/28
If the critical current density Jc is very high for a superconductor, then\nestimating its value from transport measurements is not very easy. In such\ncases, the value of Jc, called Jcm for magnetic Jc, is usually obtained from\nthe measured magnetic hysteresis loop measurements by using a proper critical\nstate model such as Bean's model (ref. 1). However, for bulk polycrystalline\nhigh temperature superconductors, the values of Jcm are much higher than the\nvalues, Jct, obtained from the transport measurements. This is due to the fact\nthat the Jct is interrupted by weakly linked grain boundaries. However, for the\nrecently discovered superconductor MgB2 (ref. 2), the grain boundary effect is\nnegligible and these two values seem to coincide. Moreover, Jc increases\ndrastically with decreasing the temperature. Consequently, the critical current\ndensities for bulk wires can be very high, suggesting that numerous\napplications for the power transport. In this letter, we report the origin of\nthe large current carrying capability of MgB2 based on direct measurements of\nthe current-voltage relation in high magnetic fields. A strong coupling between\nthe grains may be one reason for the absence of the weak link effect. Another\nreason may be the fact that, instead of a weak pinning mechanism such as\nthermally activated flux hopping, strong pinning due to a vortex glass phase is\nfound in this material. The vortex phase diagram obtained from transport\nmeasurements shows that, in H-T space, a wide region below the Hc2 line is\ncovered by a vortex glass phase.\n