The Quantum Hall Plateau-to-Plateau transition is a long-standing problem that has not yet been solved. Around the critical point, very different critical exponents of the localization length have been gotten experimentally. We approach this problem by doing experiments in the alloy disorder, which is realized in the Al_xGa_(1-x)As-Al_(0.32)Ga_(0.68)As heterostructure. By measuring directly the alloy scattering rate, we found the alloy disorder to be strong (1.13eV), short-range (atomic size) and temperature-independents. By controlling the Aluminum concentration x, we make systems dominated by the short-range alloy disorder, where quantum mechanics prevails. In these systems, the scaling exponent is observed to be 0.42.
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