Form of Scaling Function in Quantum Hall Plateau Transitions

We have measured the temperature dependence of the resistance R _xx
and R_xy of a two-dimensional electron system in the regime of the quantum Hall plateau transition. We observe for our sample a considerable large critical exponent k ～ 0.66-0.77, which may be due to the dominant electron-phonon scattering. Further we find a simple exponential form of R_xx=R_cexp (-s) in agreement with the theoretically proposed universal scaling function.