121,812 research outputs found
Gauge Theory of Composite Fermions: Particle-Flux Separation in Quantum Hall Systems
Fractionalization phenomenon of electrons in quantum Hall states is studied
in terms of U(1) gauge theory. We focus on the Chern-Simons(CS) fermion
description of the quantum Hall effect(QHE) at the filling factor
, and show that the successful composite-fermions(CF) theory
of Jain acquires a solid theoretical basis, which we call particle-flux
separation(PFS). PFS can be studied efficiently by a gauge theory and
characterized as a deconfinement phenomenon in the corresponding gauge
dynamics. The PFS takes place at low temperatures, , where
each electron or CS fermion splinters off into two quasiparticles, a fermionic
chargeon and a bosonic fluxon. The chargeon is nothing but Jain's CF, and the
fluxon carries units of CS fluxes. At sufficiently low temperatures , fluxons Bose-condense uniformly and (partly)
cancel the external magnetic field, producing the correlation holes. This
partial cancellation validates the mean-field theory in Jain's CF approach.
FQHE takes place at as a joint effect of (i) integer QHE of
chargeons under the residual field and (ii) Bose condensation of
fluxons. We calculate the phase-transition temperature and the CF
mass. PFS is a counterpart of the charge-spin separation in the t-J model of
high- cuprates in which each electron dissociates into holon and
spinon. Quasiexcitations and resistivity in the PFS state are also studied. The
resistivity is just the sum of contributions of chargeons and fluxons, and
changes its behavior at , reflecting the change of
quasiparticles from chargeons and fluxons at to electrons at
.Comment: 18 pages, 7 figure
Charge fluctuations in the slave fermion representation of the t - J model - evidence for phase separation from loop corrections
We investigate the charge density correlation function in the slave fermion representation of the two-dimensional t - J model using the self-consistent perturbation approach developed for that model by Li et al (1992 Phys. Rev. B 45 5428), which to lowest order in (t, J) gives a diagrammatic equivalent to the usual mean field theory. At the lowest order the equal-time correlation function (interpreted as the holon density correlation function) shows similar features to the results of recent high-temperature series calculations. However the loop corrections, representing scattering of holes by the antiferromagnetic spin fluctuations, lead to a divergent compressibility at low temperatures for low hole dopings and small J/t, which we interpret as indicating a tendency towards phase separation at a temperature .Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48875/2/c62504.pd
Dual Vortex Theory of Strongly Interacting Electrons: Non-Fermi Liquid to the (Hard) Core
As discovered in the quantum Hall effect, a very effective way for
strongly-repulsive electrons to minimize their potential energy is to aquire
non-zero relative angular momentum. We pursue this mechanism for interacting
two-dimensional electrons in zero magnetic field, by employing a representation
of the electrons as composite bosons interacting with a Chern-Simons gauge
field. This enables us to construct a dual description in which the fundamental
constituents are vortices in the auxiliary boson fields. The resulting
formalism embraces a cornucopia of possible phases. Remarkably,
superconductivity is a generic feature, while the Fermi liquid is not --
prompting us to conjecture that such a state may not be possible when the
interactions are sufficiently strong. Many aspects of our earlier discussions
of the nodal liquid and spin-charge separation find surprising incarnations in
this new framework.Comment: Modified dicussion of the hard-core model, correcting several
mistake
Spin-charge separation in the single hole doped Mott antiferromagnet
The motion of a single hole in a Mott antiferromagnet is investigated based
on the t-J model. An exact expression of the energy spectrum is obtained, in
which the irreparable phase string effect [Phys. Rev. Lett. 77, 5102 (1996)] is
explicitly present. By identifying the phase string effect with spin backflow,
we point out that spin-charge separation must exist in such a system: the doped
hole has to decay into a neutral spinon and a spinless holon, together with the
phase string. We show that while the spinon remains coherent, the holon motion
is deterred by the phase string, resulting in its localization in space. We
calculate the electron spectral function which explains the line shape of the
spectral function as well as the ``quasiparticle'' spectrum observed in
angle-resolved photoemission experiments. Other analytic and numerical
approaches are discussed based on the present framework.Comment: 16 pages, 9 figures; references updated; to appear in Phys. Rev.
Lattice Pseudospin Model for Quantum Hall Bilayers
We present a new theoretical approach to the study of quantum Hall
bilayer that is based on a systematic mapping of the microscopic Hamiltonian to
an anisotropic SU(4) spin model on a lattice. To study the properties of this
model we generalize the Heisenberg model Schwinger boson mean field theory
(SBMFT) of Arovas and Auerbach to spin models with anisotropy. We calculate the
temperature dependence of experimentally observable quantities, including the
spin magnetization, and the differential interlayer capacitance. Our theory
represents a substantial improvement over the conventional Hartree-Fock picture
which neglects quantum and thermal fluctuations, and has advantages over
long-wavelength effective models that fail to capture important microscopic
physics at all realistic layer separations. The formalism we develop can be
generalized to treat quantum Hall bilayers at filling factor .Comment: 26 pages, 10 figures. The final version, to appear in PR
Hidden Non-Abelian Gauge Symmetries in Doped Planar Antiferromagnets
We investigate the possibility of hidden non-Abelian Local Phase symmetries
in large-U doped planar Hubbard antiferromagnets, believed to simulate the
physics of two-dimensional (magnetic) superconductors. We present a spin-charge
separation ansatz, appropriate to incorporate holon spin flip, which allows for
such a hidden local gauge symmetry to emerge in the effective action. The group
is of the form , where SU(2) is a local
non-Abelian group associated with the spin degrees of freedom, U_E(1) is that
of ordinary electromagnetism, associated with the electric charge of the holes,
and U_S(1) is a `statistical' Abelian gauge group pertaining to the fractional
statistics of holes on the spatial plane. In a certain regime of the parameters
of the model, namely strong U_S(1) and weak SU(2), there is the possibility of
dynamical formation of a holon condensate. This leads to a dynamical breaking
of . The resulting Abelian effective theory is closely related
to an earlier model proposed as the continuum limit of large-spin planar doped
antiferromagnets, which lead to an unconventional scenario for two-dimensional
parity-invariant superconductivity.Comment: 32 pages LATEX, one figure. (More details given in the passage from
the Hubbard model to the long wavelength lattice gauge theory; one figure
added; no changes in the conclusions.
Dual Order Parameter for the Nodal Liquid
The guiding conception of vortex-condensation-driven Mott insulating behavior
is central to the theory of the nodal liquid. We amplify our earlier
description of this idea and show how vortex condensation in 2D electronic
systems is a natural extension of 1D Mott insulating and 2D bosonic Mott
insulating behavior. For vortices in an underlying superconducting pair field,
there is an important distinction between the condensation of flux hc/2e and
flux hc/e vortices. The former case leads to spin-charge confinement,
exemplified by the band insulator and the charge-density-wave. In the latter
case, spin and charge are liberated leading directly to a 2D Mott insulator
exhibiting *spin-charge separation*. Possible upshots include not only the
nodal liquid, but also a novel undoped antiferromagnetic insulating phase with
gapped excitations exhibiting spin-charge separation.Comment: 16 pages, 2 figure
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