Scaling in the angular dependence of the critical current and temperature-dependent anisotropy ratio in Bi2Sr2CaCu2O8

We present measurements of the critical current in an epitaxial Bi2Sr2CaCu2O8 film as a function of the magnetic field, the temperature, and of the angle theta between the field and the a, b planes. The orientational study reveals an increasing anisotropy in J(c) with increasing temperature. The isothermal curves J(c)(H) taken at various angles 0-degrees less-than-or-equal-to theta less-than-or-equal-to 90-degrees are found to collapse to a single curve when the magnetic field is normalized to a scaling function f(theta): J(c)(H,theta)=J(c)[H/f(theta)]. The best fit for f(theta) is obtained using an expression originally derived for H(c2)(T,theta) by Tinkham. The increase in J(c)(0-degrees)/J(c)(90-degrees) with increasing temperature is reflected by the increase in the anisotropy ratio f(0-degrees)/f(90-degrees), consistent with the quasi-two-dimensional Tinkham expression. Consistently, the same model quantitatively describes the increasing anisotropy with increasing temperature.