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 ${\ensuremath{\sigma}}_xy$. The transition curves of ${\ensuremath{\sigma}}_xy$ 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 $\ensuremath{\nu}$ for the localization length and $p$ for the coherence length are separately evaluated as $\ensuremath{\nu}=2.8\ifmmode\pm\else\textpm\fi{}0.3$ and $p=3.3\ifmmode\pm\else\textpm\fi{}0.3$.