Global phase diagram for the quantum Hall effect: An experimental picture

TL;DR

This paper presents an experimental phase diagram for the quantum Hall effect, showing how extended states merge at low magnetic fields and explaining transitions between insulator and fractional quantum Hall states.

Contribution

It constructs an experimental phase diagram for the integer and fractional quantum Hall effects based on measurements in silicon, revealing state merging and transition behaviors.

Findings

Extended states merge as magnetic field approaches zero.

Constructed a disorder vs filling factor phase diagram.

Observed direct transitions between insulator and fractional QHE states.

Abstract

We study the behavior of the extended states of a two-dimensional electron system in silicon in a magnetic field, B. Our results show that the extended states, corresponding to the centers of different Landau levels, merge with the lowest extended state as B --> 0. Using our data, we construct an experimental-based ``disorder vs filling factor'' phase diagram for the integer quantum Hall effect (QHE). Generalizing this diagram to the case of the fractional QHE, we show that it is consistent with the recently observed direct transitions between insulator and FQHE at 2/5, 2/7, and 2/9.