2,755 research outputs found
Wavefunctional approach to the bilayer \nu =1 system and a possibility for a double non-chiral pseudospin liquid
We systematically discuss candidate wave functions for the ground state of
the bilayer \nu = 1 as the distance between the layers is varied. Those that
describe increased intralayer correlations at finite distance show a departure
from the superflid description for smaller distances. They may support finite
energy meron excitations and a dissipative collective mode in the place of the
Goldstone mode of the ordered phase i.e. describe a vortex metal phase, or
imply even an incompressible, pseudospin liquid, behavior. Therefore they
describe possible outcomes of quantum disordering at finite distance between
the layers. The vortex metal phase may show up in experiments in the presence
of disorder at lower temperatures and explain the observed "imperfect
superfluidity", and the pseudospin liquid phase may be the cause of the
thermally activated (gapped) behavior of the longitudinal and Hall resistances
at higher temperatures in counterflow experiments.Comment: 10 pages, 4 figure
Pairing via Index theorem
This work is motivated by a specific point of view: at short distances and
high energies the undoped and underdoped cuprates resemble the -flux phase
of the t-J model. The purpose of this paper is to present a mechanism by which
pairing grows out of the doped -flux phase. According to this mechanism
pairing symmetry is determined by a parameter controlling the quantum tunneling
of gauge flux quanta. For zero tunneling the symmetry is ,
while for large tunneling it is . A zero-temperature critical
point separates these two limits
Ground state, quasi-hole, a pair of quasihole wavefunctions and instability in bilayer quantum Hall systems
Bilayer quantum Hall system (BLQH) differ from its single layer counterparts
(SLQH) by its symmetry breaking ground state and associated neutral gapless
mode in the pseudo-spin sector. Due to the gapless mode, qualitatively good
groundstate and low energy excited state wavefunctions at any finite distance
is still unknown. We investigate this important open problem by the Composite
Boson (CB) theory developed by one of the authors to study BLQH systematically.
We derive the ground state, quasi-hole and a pair of quasihole wavefunctions
from the CB theory and its dual action. We find that the ground state
wavefunction differs from the well known wavefunction at any finite . In addition to commonly known multiplicative factors, the quasi-hole and a
pair of quasi-holes wavefunctions also contain non-trivial normalization
factors multiplying the correct ground state wavefunction. All the distance
dependencies in all the wavefunctions are encoded in the spin part of the
ground state wavefunction. The instability encoded in the spin part of the
groundstate wavefunction leads to the pseudo-spin density wave formation
proposed by one of the authors previously. Some subtleties related to the
Lowest Landau Level (LLL) projection of the wavefunctions are briefly
discussed.Comment: 9 pages, 1 figure, REVTEX, Final version to appear in Phys. Rev.
Hierarchy wave functions--from conformal correlators to Tao-Thouless states
Laughlin's wave functions, describing the fractional quantum Hall effect at
filling factors , can be obtained as correlation functions in
conformal field theory, and recently this construction was extended to Jain's
composite fermion wave functions at filling factors . Here we
generalize this latter construction and present ground state wave functions for
all quantum Hall hierarchy states that are obtained by successive condensation
of quasielectrons (as opposed to quasiholes) in the original hierarchy
construction. By considering these wave functions on a cylinder, we show that
they approach the exact ground states, the Tao-Thouless states, when the
cylinder becomes thin. We also present wave functions for the multi-hole
states, make the connection to Wen's general classification of abelian quantum
Hall fluids, and discuss whether the fractional statistics of the
quasiparticles can be analytically determined. Finally we discuss to what
extent our wave functions can be described in the language of composite
fermions.Comment: 9 page
Meron excitations in the nu =1 quantum Hall bilayer and the plasma analogy
We study meron quasiparticle excitations in the \nu = 1 quantum Hall bilayer.
Considering the well known single meron state, we introduce its effective form,
valid in the longdistance limit. That enables us to propose two (and more)
meron states in the same limit. Further, establishing a plasma analogy of the
(111) ground state, we find the impurities that play the role of merons and
derive meron charge distributions. Using the introduced meron constructions in
generalized (mixed) ground states and corresponding plasmas for arbitrary
distance between the layers, we calculate the interaction between the
construction implied impurities. We also find a correspondence between the
impurity interactions and meron interactions. This suggests a possible
explanation of the deconfinement of the merons recently observed in the
experiments.Comment: 5 pages, 3 figure
Fractional Quantum Hall Effect and vortex lattices
It is demonstrated that all observed fractions at moderate Landau level
fillings for the quantum Hall effect can be obtained without recourse to the
phenomenological concept of composite fermions. The possibility to have the
special topologically nontrivial many-electron wave functions is considered.
Their group classification indicates the special values of of electron density
in the ground states separated by a gap from excited states
MACHOs, White Dwarfs, and the Age of the Universe
(Abridged Abstract) A favored interpretation of recent microlensing
measurements towards the Large Magellanic Cloud implies that a large fraction
(i.e. 10--50%) of the mass of the galactic halo is composed of white dwarfs. We
compare model white dwarf luminosity functions to the data from the
observational surveys in order to determine a lower bound on the age of any
substantial white dwarf halo population (and hence possibly on the age of the
Universe). We compare various theoretical white dwarf luminosity functions, in
which we vary hese three parameters, with the abovementioned survey results.
From this comparison, we conclude that if white dwarfs do indeed constitute
more than 10% of the local halo mass density, then the Universe must be at
least 10 Gyr old for our most extreme allowed values of the parameters. When we
use cooling curves that account for chemical fractionation and more likely
values of the IMF and the bolometric correction, we find tighter limits: a
white dwarf MACHO fraction of 10% (30%) requires a minimum age of 14 Gyr (15.5
Gyr). Our analysis also indicates that the halo white dwarfs almost certainly
have helium-dominated atmospheres.Comment: Final version accepted for publication, straight TeX formate, 6 figs,
22 page
Spin Susceptibility and Gap Structure of the Fractional-Statistics Gas
This paper establishes and tests procedures which can determine the electron
energy gap of the high-temperature superconductors using the model
with spinon and holon quasiparticles obeying fractional statistics. A simpler
problem with similar physics, the spin susceptibility spectrum of the spin 1/2
fractional-statistics gas, is studied. Interactions with the density
oscillations of the system substantially decrease the spin gap to a value of
, much less than the mean-field value of
. The lower few Landau levels remain visible, though broadened
and shifted, in the spin susceptibility. As a check of the methods, the
single-particle Green's function of the non-interacting Bose gas viewed in the
fermionic representation, as computed by the same approximation scheme, agrees
well with the exact results. The same mechanism would reduce the gap of the
model without eliminating it.Comment: 35 pages, written in REVTeX, 16 figures available upon request from
[email protected]
Statistical Interparticle Potential between Two Anyons
The density matrix of a two-anyon system is evaluated and used to investigate
the "statistical interparticle potential" following the theory of Uhlenbeck.
The main purpose is to see how the statistical potential will depend on the
fractional statistical parameter . The result shows that the
statistical potential for a two-anyon system with is
always repulsive. For the system with , the potential is
repulsive at short distances and becomes attractive at long distances. It
remains only in the boson system () that the repulsive potential
arising from the exclusion principle can disappear and lead to an attractive
potential at all distances.Comment: Latex 5 pages, correct typos and figur
Quantum Hall quasielectron operators in conformal field theory
In the conformal field theory (CFT) approach to the quantum Hall effect, the
multi-electron wave functions are expressed as correlation functions in certain
rational CFTs. While this approach has led to a well-understood description of
the fractionally charged quasihole excitations, the quasielectrons have turned
out to be much harder to handle. In particular, forming quasielectron states
requires non-local operators, in sharp contrast to quasiholes that can be
created by local chiral vertex operators. In both cases, the operators are
strongly constrained by general requirements of symmetry, braiding and fusion.
Here we construct a quasielectron operator satisfying these demands and show
that it reproduces known good quasiparticle wave functions, as well as predicts
new ones. In particular we propose explicit wave functions for quasielectron
excitations of the Moore-Read Pfaffian state. Further, this operator allows us
to explicitly express the composite fermion wave functions in the positive Jain
series in hierarchical form, thus settling a longtime controversy. We also
critically discuss the status of the fractional statistics of quasiparticles in
the Abelian hierarchical quantum Hall states, and argue that our construction
of localized quasielectron states sheds new light on their statistics. At the
technical level we introduce a generalized normal ordering, that allows us to
"fuse" an electron operator with the inverse of an hole operator, and also an
alternative approach to the background charge needed to neutralize CFT
correlators. As a result we get a fully holomorphic CFT representation of a
large set of quantum Hall wave functions.Comment: minor changes, publishe
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