Bloch Ferromagnetism of Composite Fermions

Abstract

In 1929 Felix Bloch suggested that the paramagnetic Fermi sea of electrons should make a spontaneous transition to a fully-magnetized state at very low densities, because the exchange energy gained by aligning the spins exceeds the enhancement in the kinetic energy. We report here the observation of an abrupt, interaction-driven transition to full magnetization, highly reminiscent of Bloch ferromagnetism that has eluded experiments for the last ninety years. Our platform is the exotic two-dimensional Fermi sea of composite fermions at half-filling of the lowest Landau level. Via quantitative measurements of the Fermi wavevector, which provides a direct measure of the spin polarization, we observe a sudden transition from a partially-spin-polarized to a fully-spin-polarized ground state as we lower the composite fermions' density. Our detailed theoretical calculations provide a semi-quantitative account of this phenomenon.

References in corpus (18)

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• Direct observation of composite fermions and their fully spin-polarized Fermi sea near $\nu =5/2$
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Cited by in corpus (16)

• Ultra-high quality two-dimensional electron systems
• Observation of spontaneous valley polarization of itinerant electrons
• Anisotropic, two-dimensional, disordered Wigner solid
• Even-Denominator Fractional Quantum Hall State at Filling Factor ν = 3/4
• Composite fermion pairing induced by Landau level mixing
• Robust Quantum Hall Ferromagnetism near a Gate-Tuned ν = 1 Landau Level Crossing
• Excitons and trions in monolayer semiconductors with correlated electrons
• Origin of the $\nu =1/2$ fractional quantum Hall effect in wide quantum wells
• Quantum Monte Carlo study of the phase diagram of the two-dimensional uniform electron liquid
• Revisiting excitation gaps in the fractional quantum Hall effect
• Composite Fermion Mass
• Valley polarization transition in a two-dimensional electron gas
• Competing Many-Body Phases at Small Fillings in Ultrahigh-Quality GaAs 2D Hole Systems: Role of Landau Level Mixing
• Quantum Hall valley Ferromagnets as a platform for topologically protected quantum memory
• Weiss Oscillations in the Galilean-Invariant Dirac Composite Fermion Theory for Even-Denominator Filling Fractions of the Lowest Landau Level
• Reentrant Bloch ferromagnetism