2007/07/31 by R. Cote, R. Côté, Dominique Boisvert +6 · 3 citations
Physics and Astronomy · #Physics of Superconductivity and Magnetism #Quantum and electron transport phenomena #Topological Materials and Phenomena #cond-mat.mes-hall
paper · pdf · doi:10.1103/physrevb.76.125320
published as Phys. Rev. B 76, 125320 (2007) · 16 pages and 12 eps figures
arxiv created 2007/07/31 · openalex publication_date 2007/09/24 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
The two-dimensional electron gas (2DEG) in a bilayer quantum Hall system can sustain an interlayer coherence at filling factor \ensuremathν=1 even in the absence of tunneling between the layers. This system, which can be described as a quantum Hall pseudospin ferromagnet, has low-energy charged excitations which may carry textures in real spin or pseudospin. Away from filling factor \ensuremathν=1, a finite density of these is present in the ground state of the 2DEG and forms a crystal. Depending on the relative size of the various energy scales, such as tunneling (\ensuremathΔSAS), Zeeman coupling (\ensuremathΔZ), or electrical bias (\ensuremathΔb), these textured crystal states can involve spin, pseudospin, or both intertwined. This last case is a ``CP3 skyrmion crystal.'' In this paper, we present a comprehensive numerical study of the collective excitations of these textured crystals using the generalized random-phase approximation. For the pure spin case, at finite Zeeman coupling the state is a skyrmion crystal with a gapless phonon mode and a separate goldstone mode that arises from a broken U(1) symmetry. At zero Zeeman coupling, we demonstrate that the constituent skyrmions break up, and the resulting state is a meron crystal with four gapless modes. In contrast, a pure pseudospin-skyrme crystal at finite tunneling has only the phonon mode. For \ensuremathΔSAS\ensuremath→0, the state evolves into a meron crystal and supports an extra gapless [U(1)] mode in addition to the phonon. For a CP3 skyrmion crystal, we find a U(1) gapless mode in the presence of nonvanishing symmetry-breaking fields \ensuremathΔSAS, \ensuremathΔZ, and \ensuremathΔb. In addition, a second mode with a very small gap is present in the spectrum. We present dispersion relations for the different low-energy modes of these various crystals as well as their physical interpretations.