Shielding currents and current-voltage characteristics of Bi 2Sr 2Ca 1Cu 2O 8+δ single crystal

Abstract

The dependence of the irreversible magnetization on the external magnetic field sweep rate, d H e/d t, and its time relaxation are studied in a Bi 2+ x Sr 2+ y Ca 1+ z Cu 2O 8+δ ( x=0.11, y=0.12, z=-0.25) single crystal. Two characteristic regions are found with a transition temperature T∗ between 15 and 20 K depending on d H e/d t and relaxation time. Below T∗ the magnetic field dependence of the shielding currents follows a scaling law J s ( H e , T)/ J s (0, T)= f[ H e / J s (0,T)] with a universal function f independent of temperature and sweep rate of magnetic field. Voltage-current characteristics are described quite well by a power-like law E/ E c =( J s / J c ) n with n∼1/ T. Above T∗ a deviation from the J s( H e) scaling behavior and a transition to much steeper voltage-current characteristics are observed. Possible reasons of these different shielding current behaviours are discussed.