DESTRUCTION OF THE QUANTUM HALL EFFECT WITH INCREASING DISORDER

TL;DR

This study experimentally investigates how increasing disorder affects the quantum Hall state in a two-dimensional electron system, revealing that the extended state floats up in energy leading to a transition from quantum Hall to insulating behavior.

Contribution

It provides experimental evidence that the extended state in the quantum Hall effect floats up in energy with increasing disorder, challenging previous assumptions about its disappearance.

Findings

Extended state floats up in energy with increasing disorder.

Transition from quantum Hall to insulating state observed.

Conductivity shows metallic temperature dependence at transition.

Abstract

We report experimental studies of disorder-induced transitions between quantum-Hall, metallic, and insulating states in a very dilute two-dimensional electron system in silicon at a magnetic field corresponding to Landau level filling factor $\nu=1$. At low disorder, the lowest extended state at $\nu=1$ is below the Fermi energy so that the system is in the quantum Hall state. Our data show that with increasing disorder (but at constant electron density and magnetic field), the extended state DOES NOT DISAPPEAR BUT FLOATS UP IN ENERGY SO THAT THE SYSTEM BECOMES INSULATING. As the extended state crosses the Fermi energy, the conductivity $\sigma_{xx}\sim e^2/2h$ has temperature dependence characteristic of a metallic system.