Experimental evidence for finite-width edge channels in integer and fractional quantum Hall effects

We report our transport study of a narrow and low-density two-dimensional electron system (2DES) defined by a pair of split gates, in the integer (IQHE) and fractional quantum Hall effect (FQHE) regimes. The gate-bias-dependent breakdown on the high and low magnetic field side of the IQHE and FQHE diagonal resistance minima is studied. In the IQHE case, edge states of width comparable to the magnetic length, in the single-electron Landau-level picture, cannot explain the observed breakdown data and much wider edge channels (wide band of edge states) are needed. These wide edge channels are interpreted as the compressible regions when the 2DES near the sample boundary phase separates into compressible and incompressible regions. The same breakdown behavior is observed in the fractional quantum Hall state and is interpreted as a similar phase separation in the FQHE regime.