Spin-pairing instabilities at the coincidence of two Landau levels

TL;DR

This paper investigates how interactions near the coincidence of two Landau levels with opposite spins can induce a spin-singlet ground state with an energy gap, explaining recent observations in fractional quantum Hall effect experiments.

Contribution

It demonstrates that gauge field fluctuations induce an effective attraction leading to a spin-singlet state at Landau level coincidence, a novel insight into FQHE spin phenomena.

Findings

Effective attractive interaction induced by gauge field fluctuations.

Existence of a spin-singlet ground state with an energy gap.

Consistency with observed half-polarized states in FQHE.

Abstract

The effect of interactions near the coincidence of two Landau levels with opposite spins at filling factor 1/2 is investigated. By mapping to Composite Fermions it is shown that the fluctuations of the gauge field induces an effective attractive Fermion interaction. This can lead to a spin-singlet ground state that is separated from the excited states by a gap. The magnitude of the gap is evaluated. The results are consistent with the recently observed half-polarized states in the FQHE at a fixed filling factor. It is suggested that similar anomalies exist for other spin configurations in degenerate spin-up and spin-down Landau levels. An experiment for testing the spin-singlet state is proposed.