Observation of a linear temperature dependence of the critical current density in a Ba0.63K0.37BiO3 single crystal

For a Ba0.63K0.37BiO3 single crystal with T(c)approximate to 31 K, H(c1)app roximate to 750 Oe at 5 K, and dimensions 3x3x1 mm(3), the temperature and field dependences of magnetic hysteresis loops have been measured within 5- 25 K in magnetic fields up to 6 Tesla. The critical current density is J(c) (0) approximate to1.5 x 10(5) A/cm(2) at zero field and 1 x 10(5) A/cm(2) a t 1 kOe at 5 K. J(c) decreases exponentially with increasing field up to 10 kOe. A linear temperature dependence of J(c) is observed below 25 K, which differs from the exponential and the power-law temperature dependences in high-T-c superconductors including the BKBO. The linear temperature depende nce can be regarded as an intrinsic effect in superconductors.