  We report quantum Hall effect breakdown of a local filling factor v_local = 1
state formed in a bulk v_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
v_local = 1 system breaks down due to inter-edge electron tunneling. At high
bias, the incompressibility of the v_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.

Mesoscale and Nanoscale Physics