Cascade of Quantum Phase Transitions in Tunnel-Coupled Edge States

We report on the cascade of quantum phase transitions exhibited by tunnel-coupled edge states across a quantum Hall line junction. We identify a series of quantum critical points between successive strong and weak tunneling regimes in the zero-bias conductance. Scaling analysis shows that the conductance near the critical magnetic fields $B_c$ is a function of a single scaling argument $\mathrm{\mid }B-B_c\mathrm{\mid }{T}^{-\kappa }$, where the exponent $\kappa =0.42$. This puzzling resemblance to a quantum Hall-insulator transition points to importance of interedge correlation between the coupled edge states.