Critical dynamics of superconducting Bi₂Sr₂CaCu₂O_8+δ films

We report on a systematic investigation of the critical fluctuations in the complex conductivity of epitaxially grown Bi₂Sr ₂CaCu₂O_8+δ films for T≲T _c using a two-coil inductive technique at zero applied field. We observe the static three-dimensional (3D) XY critical exponent in the superfluid density near T_c. Linear scaling analysis close to the critical temperature yields a dynamic critical exponent of z≈2.0 for small drive currents, but nonlinear effects are seen to be important. At T _c, a nonlinear scaling analysis also yields a 3D dynamic exponent of z = 2.0 ± 0.1.