223 research outputs found
Theory of Resonant Raman Scattering in One Dimensional Electronic systems
A theory of resonant Raman scattering spectroscopy of one dimensional
electronic systems is developed on the assumptions that (i) the excitations of
the one dimensional electronic system are described by the Luttinger Liquid
model, (ii) Raman processes involve virtual excitations from a filled valence
band to an empty state of the one dimensional electronic system and (iii)
excitonic interactions between the valence and conduction bands may be
neglected. Closed form analytic expressions are obtained for the Raman
scattering cross sections, and are evaluated analytically and numerically for
scattering in the polarized channel, revealing a "double-peak" structure with
the lower peak involving multispinon excitations with total spin S=0 and the
higher peak being the conventional plasmon. A key feature of our results is a
nontrivial power law dependence, involving the Luttinger Liquid exponents, of
the dependence of the Raman cross sections on the difference of the laser
frequency from resonance. We find that near resonance the calculated ratio of
intensity in the lower energy feature to the intensity in the higher energy
feature saturates at a value of the order of unity (times a factor of the ratio
of the velocities of the two modes). We explicate the differences between the
'Luttinger liquid' and 'Fermi liquid' calculations of RRS spectra and argue
that excitonic effects, neglected in all treatments so far, are essential for
explaining the intensity ratios observed in quantum wires. We also discuss
other Luttinger liquid features which may be observed in future RRS
experiments
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
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
Topological defects and Goldstone excitations in domain walls between ferromagnetic quantum Hall effect liquids
It is shown that the low-energy spectrum of a ferromagnetic quantum Hall
effect liquid in a system with a multi-domain structure generated by an
inhomogeneous bare Zeeman splitting is formed by excitations
localized at the walls between domains. For a step-like , the
domain wall spectrum includes a spin-wave with a linear dispersion and a small
gap due to spin-orbit coupling, and a low-energy topological defects. The
latter are charged and may dominate in the transport under conditions that the
percolation through the network of domain walls is provided.Comment: 4 pages, 1 fi
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
Spin-isospin textured excitations in a double layer at filling factor
We study the charged excitations of a double layer at filling factor 2 in the
ferromagnetic regime. In a wide range of Zeeman and tunneling splittings we
find that the low energy charged excitations are spin-isospin textures with the
charge mostly located in one of the layers. As tunneling increases, the parent
spin texture in one layer becomes larger and it induces, in the other layer, a
shadow spin texture antiferromagnetically coupled to the parent texture. These
new quasiparticles should be observable by measuring the strong dependence of
its spin on tunneling and Zeeman couplings.Comment: 4 pages, 4 figure
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
Skyrmions in quantum Hall ferromagnets as spin-waves bound to unbalanced magnetic flux quanta
A microscopic description of (baby)skyrmions in quantum Hall ferromagnets is
derived from a scattering theory of collective (neutral) spin modes by a bare
quasiparticle. We start by mapping the low lying spectrum of spin waves in the
uniform ferromagnet onto that of free moving spin excitons, and then we study
their scattering by the defect of charge. In the presence of this disturbance,
the local spin stiffness varies in space, and we translate it into an
inhomogeneus metric in the Hilbert space supporting the excitons. An attractive
potencial is then required to preserve the symmetry under global spin
rotations, and it traps the excitons around the charged defect. The
quasiparticle now carries a spin texture. Textures containing more than one
exciton are described within a mean-field theory, the interaction among the
excitons being taken into account through a new renormalization of the metric.
The number of excitons actually bound depends on the Zeeman coupling, that
plays the same role as a chemical potencial. For small Zeeman energies, the
defect binds many excitons which condensate. As the bound excitons have a unit
of angular momentum, provided by the quantum of magnetic flux left unbalanced
by the defect of charge, the resulting texture turns out to be a topological
excitation of charge 1. Its energy is that given by the non-linear sigma model
for the ground state in this topological sector, i.e. the texture is a
skyrmion.Comment: 17 pages, 1 figur
Spin-orbit coupling effect on quantum Hall ferromagnets with vanishing Zeeman energy
We present the phase diagram of a ferromagnetic quantum Hall effect liquid in
a narrow quantum well with vanishing single-particle Zeeman splitting,
and pronounced spin-orbit coupling. Upon decreasing
, the spin-polarization field of a liquid takes, first, the
easy-axis configuration, followed by the formation of a helical state, which
affects the transport and NMR properties of a liquid and the form of
topological defects in it. The analysis is extended over high odd integer
filling factors.Comment: This revised version takes into account easy-axis terms in the energy
and offers a corrected phase diagram of the ferromagnetic QHE liquid.
Analysis is extended over higher filling factor
Simultaneous Excitation of Spins and Pseudospins in the Bilayer Quantum Hall State
The tilting angular dependence of the energy gap was measured in the bilayer
quantum Hall state at the Landau level filling by changing the density
imbalance between the two layers. The observed gap behavior shows a continuous
transformation from the bilayer balanced density state to the monolayer state.
Even a sample with 33 K tunneling gap shows the same activation energy anomaly
reported by Murphy {\it et al.}. We discuss a possible relation between our
experimental results and the quantum Hall ferromagnet of spins and pseudospins.Comment: 4 pages, 4 figure
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