600 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
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.
Fermions in the Lowest Landau Level: Bosonization, Algebra, Droplets, Chiral Boson
We present field theoretical descriptions of massless (2+1) dimensional
nonrelativistic fermions in an external magnetic field, in terms of a fermionic
and bosonic second quantized language. An infinite dimensional algebra,
, appears as the algebra of unitary transformations which preserve
the lowest Landau level condition and the particle number. In the droplet
approximation it reduces to the algebra of area-preserving diffeomorphisms,
which is responsible for the existence of a universal chiral boson Lagrangian
independent of the electrostatic potential. We argue that the bosonic droplet
approximation is the strong magnetic field limit of the fermionic theory. The
relation to the string model is discussed.Comment: 16 page
Broken symmetry, excitons, gapless modes and topological excitations in Trilayer Quantum Hall systems
We study the interlayer coherent incompressible phase in Trilayer Quantum
Hall systems (TLQH) at total filling factor from three
approaches:
Mutual Composite Fermion (MCF), Composite Boson (CB) and wavefunction
approach.
Just like in Bilayer Quantum Hall system, CB approach is superior than
MCF approach in studying TLQH with broken symmetry. The Hall and Hall drag
resistivities are found to be quantized at . Two neutral gapless
modes with linear dispersion relations are identified and the ratio of the two
velocities is close to .
The novel excitation spectra are classified into two classes: Charge neutral
bosonic
2-body bound states and Charge fermionic 3-body bound states.
In general, there are two 2-body Kosterlize-Thouless (KT) transition
temperatures and one 3-body KT transition. The Charge 3-body
fermionic bound states may be the main dissipation source of transport
measurements.
The broken symmetry in terms of algebra is studied. The structure
of excitons and their flowing patterns are given. The coupling between the two
Goldstone modes may lead to the broadening in the zero-bias peak in the
interlayer correlated tunnelings of the TLQH. Several interesting features
unique to TLQH are outlined.
Limitations of the CB approach are also pointed out.Comment: 10 pages, 3 figures, Final version to be published in Phys. Rev.
Liouvillian Approach to the Integer Quantum Hall Effect Transition
We present a novel approach to the localization-delocalization transition in
the integer quantum Hall effect. The Hamiltonian projected onto the lowest
Landau level can be written in terms of the projected density operators alone.
This and the closed set of commutation relations between the projected
densities leads to simple equations for the time evolution of the density
operators. These equations can be used to map the problem of calculating the
disorder averaged and energetically unconstrained density-density correlation
function to the problem of calculating the one-particle density of states of a
dynamical system with a novel action. At the self-consistent mean-field level,
this approach yields normal diffusion and a finite longitudinal conductivity.
While we have not been able to go beyond the saddle point approximation
analytically, we show numerically that the critical localization exponent can
be extracted from the energetically integrated correlation function yielding
in excellent agreement with previous finite-size scaling
studies.Comment: 9 pages, submitted to PR
Uncertainty Principle and Off-Diagonal Long Range Order in the Fractional Quantum Hall Effect
A natural generalization of the Heisenberg uncertainty principle inequality
holding for non hermitian operators is presented and applied to the fractional
quantum Hall effect (FQHE). This inequality was used in a previous paper to
prove the absence of long range order in the ground state of several 1D systems
with continuous group symmetries. In this letter we use it to rule out the
occurrence of Bose-Einstein condensation in the bosonic representation of the
FQHE wave function proposed by Girvin and MacDonald. We show that the absence
of off-diagonal long range order in this 2D problem is directly connected with
the behavior of the static structure function at small momenta.Comment: 10 pages, plain TeX, UTF-09-9
Tunneling, dissipation, and superfluid transition in quantum Hall bilayers
We study bilayer quantum Hall systems at total Landau level filling factor
in the presence of interlayer tunneling and coupling to a dissipative
normal fluid. Describing the dynamics of the interlayer phase by an effective
quantum dissipative XY model, we show that there exists a critical dissipation
set by the conductance of the normal fluid. For ,
interlayer tunnel splitting drives the system to a quantum Hall state.
For , interlayer tunneling is irrelevant at low temperatures,
the system exhibits a superfluid transition to a collective quantum Hall state
supported by spontaneous interlayer phase coherence. The resulting phase
structure and the behavior of the in-plane and tunneling currents are studied
in connection to experiments.Comment: 4 RevTex pages, revised version, to appear in Phys. Rev. Let
Theory of Microwave Parametric Down Conversion and Squeezing Using Circuit QED
We study theoretically the parametric down conversion and squeezing of
microwaves using cavity quantum electrodynamics of a superconducting Cooper
pair box (CPB) qubit located inside a transmission line resonator. The
non-linear susceptibility \chi_2 describing three-wave mixing can be tuned by
dc gate voltage applied to the CPB and vanishes by symmetry at the charge
degeneracy point. We show that the coherent coupling of different cavity modes
through the qubit can generate a squeezed state. Based on parameters realized
in recent successful circuit QED experiments, squeezing of 95% ~ 13dB below the
vacuum noise level should be readily achievable.Comment: 4 pages, accepted for publication in Phys. Rev. Let
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
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