Superconducting State Properties of CuBa 2 Ca 3 Cu 4 O 10+δ .

The superconducting state properties of the CuBa 2 Ca 3 Cu 4 O 10+δ (Cu-1234) system, with a transition temperature as high as 117.5 K, were investigated. The ac magnetic susceptibility measurements confirmed a very sharp transition to the superconducting state. The upper critical field, H c2 , as high as 91 T, and the irreversibility field, H irr , as high as 21 T at 77 K, were determined using dc SQUID magnetization measurements. The intragrain critical current density, j c , estimated from a magnetic hysteresis loop, is as high as 5 × 10 9 A/m 2 in a self-generated magnetic field at 77 K. However, the intergrain critical current density in the studied material is smaller by four orders of magnitude due to very weak intergrain connections.