Two-step breakdown of a local ν=1 quantum Hall state

We report quantum Hall effect breakdown of a local filling factor nu(local) = 1 state formed in a bulk nu(bulk )= 2 system in an AlGaAs/GaAs heterostructure. When a finite source-drain bias is applied across the local system, the breakdown occurs in two steps. At low bias, quantized conductance through the nu(local) = 1 system breaks down due to interedge electron tunneling. At high bias, the incompressibility of the nu(local) = 1 system breaks down because the spin gap closes. The two steps are resolved by combining measurements of resistively detected nuclear magnetic resonance and shot noise, which allows one to evaluate electron spin polarization in the local system and spin-dependent charge transport through the system, respectively.