Fractional quantum Hall effect without energy gap

TL;DR

This study observes fractional quantum Hall effects at low magnetic fields where traditional energy gaps are absent, indicating a gapless state in a 2D electron system.

Contribution

It provides experimental evidence of fractional quantum Hall states without energy gaps in a 2DES, challenging the conventional understanding of these states.

Findings

Fractional quantum Hall states observed at low magnetic fields.

Absence of quasiparticle energy gaps at these states.

Complete suppression of thermodynamical density of states minima.

Abstract

In the fractional quantum Hall effect regime we measure diagonal ($\rho_{xx}$) and Hall ($\rho_{xy}$) magnetoresistivity tensor components of two-dimensional electron system (2DES) in gated GaAs/Al$_{x}$Ga$_{1-x}$As heterojunctions, together with capacitance between 2DES and the gate. We observe 1/3- and 2/3-fractional quantum Hall effect at rather low magnetic fields where corresponding fractional minima in the thermodynamical density of states have already disappeared manifesting complete suppression of the quasiparticle energy gaps.