Tl-Based Cu-O High Temperature Superconductors
We have discovered reproducible and stable bulk superconductivity in the Tl-Ca-Ba-Cu-0 system with zero resistance above 120 K. Magnetic and electronic transport properties including thermoelectric power and critical current of the new superconductors are presented. The Tl-Ca-Ba-Cu-O system can form a number of superconducting compounds, including TlmCan-iBa2CunOi.5m+2n+i with m = 1 and 2, and n = 1, 2, 3, and 4. The Tc increases with m and n. The 2223 (Tl:Ca:Ba:Cu) phase has the highest Tc (125 K) to date. We present Josephson junction studies on the 2223 phase showing the existence of electron pair supercurrents and demonstrating weak link behavior at 77 K. We discuss an unusual levitation phenomenon in which the 2223 phase can be suspended, above, below, or to the side of a ring shaped magnet. We also discuss a new Tl-based superconducting system, in which Sr replaces the Ba, the Tl-Ca-Sr-Cu-O system.
KeywordsOnset Temperature Nominal Composition Critical Current Density Thermoelectric Power Josephson Junction
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