Current scaling of the topological quantum phase transition between a quantum anomalous Hall insulator and a trivial insulator

We report a current scaling study of a quantum phase transition between a quantum anomalous Hall insulator and a trivial insulator on the surface of a heterostructure film of magnetic topological insulators. The transition was observed by tilting the magnetization while measuring the Hall conductivity $sigma_{xy}$. The transition curves of $sigma_{xy}$ taken under various excitation currents cross each other at a single point, exemplifying a quantum critical behavior of the transition. The slopes of the transition curves follow a power law dependence of the excitation current, giving a scaling exponent. Combining with the result of the previous temperature scaling study, critical exponents $ u$ for the localization length and $p$ for the coherence length are separately evaluated as $ u$ = 2.8 $pm$ 0.3 and $p$ = 3.3 $pm$ 0.3.