Vortex pinning by mesoscopic defects: A way to levitation at liquid oxygen temperature

摘要

The addition of long-term Zr_(2)O_(3)-ball milled Gd_(2)BaCuO_(5) particles to a standard (Nd,Eu,Gd)Ba_(2)Cu_(3)O_(y) superconductor led to a spontaneous formation of extremely small (20-50 nm) Zr-rich (Nd,Eu,Gd)-Ba-Cu-O particles during the melt-growth process. This pinning medium, approaching the interesting physical limit of point-like pins from the side of large normal ones, dramatically enhanced supercurrents up to 90 K, both in low and intermediate fields. As a result, levitation experiment could be performed with liquid oxygen as a coolant. The particle size effect resemblance with fast neutron irradiation of RE-Ba-Cu-O single crystals is discussed.