Breakdown of the integer and fractional quantum Hall states in a quantum point contact

The integer and fractional quantum Hall states are known to breakdown at high dc bias, exhibiting deviation from the ideal incompressible behavior. We measure breakdown of the ν=2, 3, 4, 5 integer and the ν=4/3 and 5/3 fractional states in a quantum point contact (QPC) of lithographic width ∼600 nm. Dependence of the critical current on magnetic field, QPC gate voltage, and QPC width are presented. Of particular interest, the critical current of the 4/3 and 5/3 fractional states shows the opposite dependence on QPC width compared to the integer states. This previously unobserved result is not explained by current theories of breakdown.