Limits of Superconductivity in Bi-2212

1. NORMAL METAL VORTEX LIQUID VORTEX GLASS Limits of Superconductivity in Bi-2212 The superconducting current is analogous to an icy river: as long as the surface is frozen, the water (current) flows smoothly underneath. When the weather warms up, the ice starts to melt and break apart, impeding the water flow. Superconductors conduct electricity without resistance. When magnetic fields are applied to superconductors, the magnetic flux lines penetrate in the form of vortices. These vortices are normally trapped in crystal imperfections and are unable to move, but at sufficiently high temperatures they can attain enough energy to escape, and disrupt the flow of superconducting current. The motion of these vortices (vortex liquid) contributes to the resistance of an applied electric current, limiting the usefulness of the superconductor. In Bi-2212, superconductivity first appears at 90K, and remains superconductor above 30T. Using 17O Nuclear Magnetic Resonance, researchers from Northwestern University, led by Prof. W. Halperin, in collaboration with A. Reyes and P. Kuhns (NHMFL) have discovered that the stable state required in high magnetic fields above 30T where the vortices remain frozen can be established only when the temperature falls below 12 K. Tm2D Tc (H) Tm(H) The magnetic-field–temperature phase diagram for vortex melting in Bi-2212 for H || c, showing the super-conducting transition Tc(H) from normal state (solid line), the melting transition, Tm(H ), separating the liquid from solid (glass) vortex (dashed line), and the two-dimensional vortex melting transition temperature, Tm2D, (red line). B. Chen, W. P. Halperin, P. Guptasarma, D. G. Hinks, V. F. Mitrović, A. P. Reyes, and P. L. Kuhns, Nature Physics, 540 (2007).