Collective excitations in double-layer quantum Hall systems

TL;DR

This paper investigates the collective excitation spectra in double-layer quantum Hall systems, revealing differences between in-phase and out-of-phase modes, and compares results with Chern-Simons-Landau-Ginzburg theory.

Contribution

It provides a detailed analysis of collective excitations using the single mode approximation, highlighting the effects of interlayer interactions and coherence.

Findings

In-phase excitations resemble single-layer systems.

Out-of-phase modes have finite oscillator strengths influenced by interlayer Coulomb interactions.

The intra-Landau-level out-of-phase mode has a gap unless spontaneous inter-layer coherence occurs.

Abstract

We study the collective excitation spectra of double-layer quantum-Hall systems using the single mode approximation. The double-layer in-phase density excitations are similar to those of a single-layer system. For out-of-phase density excitations, however, both inter-Landau-level and intra-Landau-level double-layer modes have finite dipole oscillator strengths. The oscillator strengths at long wavelengths for the latter transitions are shifted upward by interactions by identical amounts proportional to the interlayer Coulomb coupling. The intra-Landau-level out-of-phase mode has a gap when the ground state is incompressible except in the presence of spontaneous inter-layer coherence. We compare our results with predictions based on the Chern-Simons-Landau-Ginzburg theory for double-layer quantum Hall systems.