Cyclotron Orbits of Composite Fermions in the Fractional Quantum Hall Regime

TL;DR

This study reveals that composite fermions in a bilayer GaAs system exhibit well-defined cyclotron orbits influenced by a Wigner crystal in the adjacent layer, demonstrating persistent Fermi surface features in the fractional quantum Hall regime.

Contribution

First observation of geometric resonance of composite fermions with a Wigner crystal in a bilayer system, showing CFs retain Fermi surface properties deep in fractional quantum Hall states.

Findings

Resistance peaks vary nonmonotonically with WC density

Maxima occur when CF orbits enclose WC lattice points

Resonance features vanish when WC melts at 275 mK

Abstract

We study a bilayer GaAs hole system that hosts two distinct many-body phases at low temperatures and high perpendicular magnetic fields. The higher-density (top) layer develops a Fermi sea of composite fermions (CFs) in its half-filled lowest Landau level, while the lower-density (bottom) layer forms a Wigner crystal (WC) as its filling becomes very small. Owing to the inter-layer interaction, the CFs in the top-layer feel the periodic Coulomb potential of the WC in the bottom-layer. We measure the magnetoresistance of the top-layer while changing the bottom-layer density. As the WC layer density increases, the resistance peaks separating the adjacent fractional quantum Hall states in the top-layer change nonmonotonically and attain maximum values when the cyclotron orbit of the CFs encloses one WC lattice point. These features disappear at T = 275 mK when the WC melts. The observation of such geometric resonance features is unprecedented and surprising as it implies that the CFs retain a well-defined cyclotron orbit and Fermi wave vector even deep in the fractional quantum Hall regime, far from half-filling.