59 research outputs found
Wave Function of the Largest Skyrmion on a Sphere
It has been clarified that charged excitation known as a skyrmion exists
around the ferromagnetic ground state at the Landau level filling factor
, where is an odd integer. An infinite sized skyrmion is realized
in the absence of the spin-Zeeman splitting or for double-layered systems.
Analytical form of the wave function is identified at and
through exact diagonalization of the Hamiltonian for finite sized spherical
systems. It is clarified that the skyrmion wave functions at and
are qualitatively different: they are not related by the composite
fermion transformation. Long-range behavior of the skyrmion wave function
around is shown to be consistent with the semiclassical picture of the
skyrmion.Comment: 4 pages. to be published in J. Phys. Soc. Jpn. Vol.67 No.10. Three
references are adde
Shape Deformation driven Structural Transitions in Quantum Hall Skyrmions
The Quantum Hall ground state away from can be described by a
collection of interacting skyrmions. We show within the context of a nonlinear
sigma model, that the classical ground state away from is a skyrmion
crystal with a generalized N\'eel order. We show that as a function of filling
, the skyrmion crystal undergoes a triangle to square to triangle
transition at zero temperature. We argue that this structural transition,
driven by a change in the shape of the individual skyrmions, is stable to
thermal and quantum fluctuations and may be probed experimentally.Comment: 4 pages (REVTEX) and 4 .eps figure
Many skyrmion wave functions and skyrmion statistics in quantum Hall ferromagnets
We determine the charge and statistical angle of skyrmions in quantum Hall
ferromagnets by performing Berry phase calculations based on the microscopic
variational wave functions for many-skyrmion states. We find, in contradiction
to a recent claim by Dziarmaga, that both the charge and the statistical angle
of a skyrmion are independent of its spin (size), and are identical to those of
Laughlin quasiparticles at the same filling factor. We discuss some subtleties
in the use of these variational wave functions.Comment: 11 pages, RevTex, no figure. Accepted in Phys. Rev. B, Rapid
Communication
Heat Capacity Evidence for the Suppression of Skyrmions at Large Zeeman Energy
Measurements on a multilayer two-dimensional electron system (2DES) near
Landau level filling =1 reveal the disappearance of the nuclear spin
contribution to the heat capacity as the ratio between the Zeeman
and Coulomb energies exceeds a critical value 0.04. This
disappearance suggests the vanishing of the Skyrmion-mediated coupling between
the lattice and the nuclear spins as the spin excitations of the 2DES make a
transition from Skyrmions to single spin-flips above . Our
experimental is smaller than the calculated =0.054
for an ideal 2DES; we discuss possible origins of this discrepancy.Comment: Experimental paper, 6 figure
Quantum Phase Transition in Skyrmion Lattices
We investigate the ground state of 2D electron gas in Quantum Hall regime at
the filling factor slightly deviating from unity, that can be viewed as a
sparse lattice of skyrmions. We have found that in the low density limit
skyrmions are bound in pairs, those forming the actual lattice. We have shown
that at further density increase the lattice undergoes a quantum phase
transition, an analogue of superconducting phase transition in Josephson
junction arrays.Comment: 4 pages REVTEX, 3 Postscript figure
SU(N) Quantum Hall Skyrmions
We have investigated skyrmions in N-component quantum Hall systems. We find
that SU(N) skyrmions are the lowest energy charged excitations for filling
factors \nu = 1,2,...,N-1 for small enough symmetry breaking terms. N>2
skyrmions can be realized in Si QH systems based on the (110) or (111)
interfaces of Si, or perhaps in Si (100) systems, where the spin and valley
isospin together provide an SU(4)-symmetry, or in multilayer QH systems. We
also present Hartree-Fock results for a phenomenological easy-axis
SU(2)-breaking model appropriate to valley degeneracy.Comment: 5 pages, 2 figure
Skyrmion Physics Beyond the Lowest Landau Level Approximation
The effects of Landau level mixing and finite thickness of the
two-dimensional electron gas on the relative stability of skyrmion and single
spin-flip excitations at Landau level filling factor have been
investigated. Landau level mixing is studied by fixed-phase diffusion Monte
Carlo and finite thickness is included by modifying the effective Coulomb
interaction. Both Landau level mixing and finite thickness lower skyrmion
excitation energies and favor skyrmions with fewer spin flips. However, the two
effects do not work `coherently'. When finite thickness is included the effect
of Landau level mixing is strongly suppressed.Comment: 4 pages, 4 figure
Thermodynamic Phase Diagram of the Quantum Hall Skyrmion System
We numerically study the interacting quantum Hall skyrmion system based on
the Chern-Simons action. By noticing that the action is invariant under global
spin rotations in the spin space with respect to the magnetic field direction,
we obtain the low-energy effective action for a many skyrmion system.
Performing extensive molecular dynamics simulations, we establish the
thermodynamic phase diagram for a many skyrmion system.Comment: 4 pages, RevTex, 2 postscript figure
Critical Behavior of Nuclear-Spin Diffusion in GaAs/AlGaAs Heterostructures near Landau Level Filling \nu=1
Thermal measurements on a GaAs/AlGaAs heterostructure reveal that the state
of the confined two-dimensional electrons dramatically affects the nuclear-spin
diffusion near Landau level filling factor \nu=1. The experiments provide
quantitative evidence that the sharp peak in the temperature dependence of heat
capacity near \nu=1 is due to an enhanced nuclear-spin diffusion from the GaAs
quantum wells into the AlGaAs barriers. We discuss the physical origin of this
enhancement in terms the possible Skyrme solid-liquid phase transition.Comment: 1 LateX file, 3 figures, submitte
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