26,389 research outputs found

### Dynamics of edge Majorana fermions in $\nu=\frac{5}2$ fractional quantum Hall effects

Commencing with the composite fermion description of the $\nu=5/2$ fractional
quantum Hall effect, we study the dynamics of the edge neutral Majorana
fermions. We confirm that these neutral modes are chiral and show that a
conventional p-wave pairing interaction between CFs does not contribute to the
dynamics of the edge neutral fermions. We find an important bilinear coupling
between the charged and neutral modes. We show that owing to this coupling, the
dispersion of the neutral modes is linear and their velocities are proportional
to the wave vector of the charged mode. This dynamic origin of the motion of
the edge Majorana fermions was never expected before.Comment: 5 pages, published versio

### Gauge symmetry in Kitaev-type spin models and index theorems on odd manifolds

We construct an exactly soluble spin-$\frac{1}2$ model on a honeycomb
lattice, which is a generalization of Kitaev model. The topological phases of
the system are analyzed by study of the ground state sector of this model, the
vortex-free states. Basically, there are two phases, A phase and B phase. The
behaviors of both A and B phases may be studied by mapping the ground state
sector into a general p-wave paired states of spinless fermions with tunable
pairing parameters on a square lattice. In this p-wave paired state theory, the
A phase is shown to be the strong paired phase, an insulating phase. The B
phase may be either gapped or gapless determined by the generalized inversion
symmetry is broken or not. The gapped B is the weak pairing phase described by
either the Moore-Read Pfaffian state of the spinless fermions or anti-Pfaffian
state of holes depending on the sign of the next nearest neighbor hopping
amplitude. A phase transition between Pfaffian and anti-Pfaffian states are
found in the gapped B phase. Furthermore, we show that there is a hidden SU(2)
gauge symmetry in our model. In the gapped B phase, the ground state has a
non-trivial topological number, the spectral first Chern number or the chiral
central charge, which reflects the chiral anomaly of the edge state. We proved
that the topological number is identified to the reduced eta-invariant and this
anomaly may be cancelled by a bulk Wess-Zumino term of SO(3) group through an
index theorem in 2+1 dimensions.Comment: longer version, 12 pages, to be published in Nucl. Phys.

### A Microscopic Model of Edge States of Fractional Quantum Hall Liquid: From Composite Fermions to Calogero-Sutherland Model

Based on the composite fermion approach, we derive a microscopic theory
describing the low-lying edge excitations in the fractional quantum Hall liquid
with $\nu=\frac{\nu^*}{\tilde\phi\nu^*+1}$. For $\nu^*>0$, it is found that the
composite fermion model reduces to an SU$(\nu^*)$ Calogero-Sutherland model in
the one-dimensional limit, whereas it is not exact soluble for $\nu^*<0$.
However, the ground states in both cases can be found and the low-lying
excitations can be shown the chiral Luttinger liquid behaviors since a gap
exists between the right- and left-moving sectors in each branch of the
azimuthal excitations.Comment: minor revised with references adde

### Gossamer supercoductivity and the mean field approximation of a new effective Hubbard model

We construct a new effective two-dimensional Hubbard model by taking the
different electron occupancy on site into account. The mean field state of the
new Hamiltonian gives rise to the gossamer superconducting state proposed by
Laughlin recently(cond-mat/0209269).Comment: 4 pages, 2 figures,some typo errors are correcte

### Short-range coherence of a lattice Bose atom gas in the Mott insulating phase

We study the short-range coherence of ultracold lattice Bose gases in the
Mott insulating phase. We calculate the visibility of the interference pattern
and the results agree quantitatively with the recent experimental measurement
[Phys. Rev. Lett. 95, 050404 (2005)]. The visibility deviation from the
inversely linear dependence on the bare on-site interaction U_0 is explained
both in smaller and larger U_0. For a smaller U_0, it comes from a second order
correction. For a larger U_0, except the breakdown of adiabaticity as analyzed
by Gerbier et al, there might be another source to cause this deviation, which
is the diversity between $U_0$ determined by the single atom Wannier function
and the effective on site interaction U_eff for a multi-occupation per site.Comment: 4 pages, 2 figures; published in PR

### Comments on `Rashba precession in quantum wire with interaction'

In a recent Rapid Communication (Phys. Rev. B {\bf 63}, 121210(R) (2001)),
Ha\"usler showed that the interaction between electrons in quantum wires may
enhance the persistent spin current arising from Rashba spin-orbital coupling.
In this Comments, we would like to point out that this 'enhancement' comes from
a misunderstanding to the boosting persistent current in the Luttinger liquid
theory. A correct calculation will not give such an enhancement of the
persistent spin current. Meanwhile, we provide a Luttinger liquid theory with
Rashba spin-orbital interaction by bosonization, which may show how the Rashba
precession is in a Luttinger liquid.Comment: 2 page

### Seiberg-Witten monopoles: Weyl metal coupled to chiral magnets

We study a Weyl (semi)metal which couples to local magnets. In the continuum
limit, the Hamiltonian of the system matches the Chern-Simons-Maxwell-Dirac
functional and then the ground state is governed by generalized Seiberg-Witten
(SW) or Freund equations in terms of the sign of Dzyaloshinskii-Moriya
coupling. The ground states determined by the Freund equations may either be
monopolar Weyl semimetal accompanied by the ferromagnetic magnets (MWFM) or SW
monopoles which consist of spheric Weyl fermions coupled to chiral magnets,
depending on the strength of the Kondo coupling. In the latter phase, the
topological ground state is characterized by SW invariants and with a Weyl
surface on which the Weyl metal is of an exotic dispersion $\propto \sqrt k$.
There are also the metastable SW monopole solutions carrying an opposite SW
invariant for the SW equations while the ground state in this case is the MWFM
state.Comment: 5+2 pages 3 figure

### A Novel Meron-induced Pseudospin Wave in Bilayer Quantum Hall Coherent State and the Residual Zero-bias Peak in Tunneling Conductance

In the bilayer quantum Hall coherent state for $\nu_T$ deviating slightly
from one, we show that, instead of the global order parameter, the spontaneous
breaking of the pseudospin U(1) rotational symmetry is reflected by the
periodic domain structure accompanying with the charged meron pairs. The motion
of meron pairs induces a novel pseudospin wave. The long range order of the
periodic domains in a low bias voltage range leads to the residual zero-bias
peak in the tunneling conductance even when the pseudopsin Goldstone feature in
a high bias voltage range can be distinct from it.Comment: 4 pages, 1 figur

### Incompressible excitonic superfluid of ultracold Bose atoms in an optical lattice: a new superfluid phase in the one-component Bose-Hubbard model

We predict that a new superfluid phase, the incompressible excitonic
superfluid (IESF), in the phase diagram of ultracold Bose atoms in $d>1$
dimensional optical lattices, which is caused by the spontaneous breaking of
the symmetry of translation of the lattice. Within mean field theory, the
critical temperature of the phase transition from this IESF to the normal fluid
(NF) is calculated and the triple-critical point of the three phases is
determined. We also investigate both configuration and gauge field fluctuations
and show the IESF state is stable against these fluctuations. We expect this
IESF phase can be experimentally observed by loading cold Bose atoms into a
two-dimensional lattice where the atom filling fraction deviates slightly from
exact commensurations. The signatures distinguishing this IESF from the common
atom superfluid (ASF) are that (i) the critical temperature of the IEST/NF
transition is independent of interaction, unlike the ASF/NF transition; (ii)
the IESF is incompressible while the ASF is compressible.Comment: 4 pages, 2 figure

### Time-evolution stability of order parameters and phase diagrams of bosons on optical lattice

Stemming from the Heisenberg equations of motion, we study the time-evolution
stability of the order parameters for the cold atoms on optical lattices. The
requirement of this stability of the order parameters endows the phase diagram
with a fruitful structure in the superfluid phase. For the one-component
Bose-Hubbard model, we see that this stability of order parameter leads to a
physically receivable phase diagram. For two-component bosons, we show that the
molecules are preformed in the atomic superfluid and then condenses into a
molecular superfluid phase at a critical repulsive inter-species interaction,
which resembles the pre-pairing mechanism in high $T_c$ superconductor of Cu-O
cuprates.Comment: 4 pages, 2 figure

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