Entropy in the Kerr-Newman Black Hole

The entropy of the Kerr-Newman black hole is calculated in terms of the brick wall method with maintaining careful attention to the contribution of superradiant scalar modes. It turns out that the nonsuperradinat and superradiant modes are simultaneously contribute to the black hole entropy. In particular the contribution of the latter is negative. We show that since the non-rotating limit in the brick wall method is meaningless and there is a lower bound of the angular velocity, the non-rotating and rotating black holes should be treated separately. Moreover, from the lower bound of the angular velocity, we obtain the $\theta$-dependence structure of the brick wall cutoff. The $\theta$-dependence structure naturally requires the angular cutoff $\delta$. Finally, if the cutoff values, the radial cutoff $\epsilon$ and the angular cutoff $\delta$, satisfy a proper relation between them, the resulting entropy satisfies the area law.