Robust Quantum Hall Ferromagnetism near a Gate-Tuned ν = 1 Landau Level Crossing

Abstract

In a low-disorder two-dimensional electron system, when two Landau levels of opposite spin or pseudospin cross at the Fermi level, the dominance of the exchange energy can lead to a ferromagnetic, quantum Hall ground state whose gap is determined by the exchange energy and has skyrmions as its excitations. This is normally achieved via applying either hydrostatic pressure or uniaxial strain. We study here a very high-quality, low-density, two-dimensional hole system, confined to a 30-nm-wide (001) GaAs quantum well, in which the two lowest-energy Landau levels can be gate tuned to cross at and near filling factor $\nu =1$. As we tune the field position of the crossing from one side of $\nu =1$ to the other by changing the hole density, the energy gap for the quantum Hall state at $\nu =1$ remains exceptionally large, and only shows a small dip near the crossing. The gap overall follows a $\sqrt{B}$ dependence, expected for the exchange energy. Our data are consistent with a robust quantum Hall ferromagnet as the ground state.

7+2 pages, 4+4 figures

References in corpus (12)

• Quantum Hall Ferromagnetism in Graphene
• Landau Level Splitting in Graphene in High Magnetic Fields
• Valley splitting of AlAs two-dimensional electrons in a perpendicular magnetic field
• Observation of Quantum Hall Valley Skyrmions
• Observation of Spontaneous Ferromagnetism in a Two-Dimensional Electron System
• Thermal and quantum melting phase diagrams for a magnetic-field-induced Wigner solid
• Density and well width dependences of the effective mass of twodimensional holes in (100) GaAs quantum wells measured by cyclotron resonance at microwave frequencies
• Spontaneous valley polarization of interacting carriers in a monolayer semiconductor
• Bloch Ferromagnetism of Composite Fermions
• Dependence of persistent gaps at Landau level crossings on relative spin
• Discovery of an insulating ferromagnetic phase of electrons in two dimensions
• Fixed-phase diffusion Monte Carlo study of the activation gap and the skyrmion excitation of $\nu =1$ system in the presence of charged impurities