2,250 research outputs found
Quantum spin Hall effect and spin-charge separation in a kagome lattice
A two-dimensional kagome lattice is theoretically investigated within a
simple tight-binding model, which includes the nearest neighbor hopping term
and the intrinsic spin-orbit interaction between the next nearest neighbors. By
using the topological winding properties of the spin-edge states on the
complex-energy Riemann surface, the spin Hall conductance is obtained to be
quantized as () in insulating phases. This result keeps
consistent with the numerical linear-response calculation and the
\textbf{Z} topological invariance analysis. When the sample boundaries
are connected in twist, by which two defects with flux are introduced, we
obtain the spin-charge separated solitons at 1/3 (or 2/3) filling.Comment: 13 NJP pages, 7 figure
Modulation Equations: Stochastic Bifurcation in Large Domains
We consider the stochastic Swift-Hohenberg equation on a large domain near
its change of stability. We show that, under the appropriate scaling, its
solutions can be approximated by a periodic wave, which is modulated by the
solutions to a stochastic Ginzburg-Landau equation. We then proceed to show
that this approximation also extends to the invariant measures of these
equations
Calculating critical temperatures of superconductivity from a renormalized Hamiltonian
It is shown that one can obtain quantitatively accurate values for the
superconducting critical temperature within a Hamiltonian framework. This is
possible if one uses a renormalized Hamiltonian that contains an attractive
electron-electron interaction and renormalized single particle energies. It can
be obtained by similarity renormalization or using flow equations for
Hamiltonians. We calculate the critical temperature as a function of the
coupling using the standard BCS-theory. For small coupling we rederive the
McMillan formula for Tc. We compare our results with Eliashberg theory and with
experimental data from various materials. The theoretical results agree with
the experimental data within 10%. Renormalization theory of Hamiltonians
provides a promising way to investigate electron-phonon interactions in
strongly correlated systems.Comment: 6 pages, LaTeX, using EuroPhys.sty, one eps figure included, accepted
for publication in Europhys. Let
Temperature in One-Dimensional Bosonic Mott insulators
The Mott insulating phase of a one-dimensional bosonic gas trapped in optical
lattices is described by a Bose-Hubbard model. A continuous unitary
transformation is used to map this model onto an effective model conserving the
number of elementary excitations. We obtain quantitative results for the
kinetics and for the spectral weights of the low-energy excitations for a broad
range of parameters in the insulating phase. By these results, recent Bragg
spectroscopy experiments are explained. Evidence for a significant temperature
of the order of the microscopic energy scales is found.Comment: 8 pages, 7 figure
Symmetric Hyperbolic System in the Self-dual Teleparallel Gravity
In order to discuss the well-posed initial value formulation of the
teleparallel gravity and apply it to numerical relativity a symmetric
hyperbolic system in the self-dual teleparallel gravity which is equivalent to
the Ashtekar formulation is posed. This system is different from the ones in
other works by that the reality condition of the spatial metric is included in
the symmetric hyperbolicity and then is no longer an independent condition. In
addition the constraint equations of this system are rather simpler than the
ones in other works.Comment: 8 pages, no figure
Tensor mass and particle number peak at the same location in the scalar-tensor gravity boson star models - an analytical proof
Recently in boson star models in framework of Brans-Dicke theory, three
possible definitions of mass have been identified, all identical in general
relativity, but different in scalar-tensor theories of gravity.It has been
conjectured that it's the tensor mass which peaks, as a function of the central
density, at the same location where the particle number takes its maximum.This
is a very important property which is crucial for stability analysis via
catastrophe theory. This conjecture has received some numerical support. Here
we give an analytical proof of the conjecture in framework of the generalized
scalar-tensor theory of gravity, confirming in this way the numerical
calculations.Comment: 9 pages, latex, no figers, some typos corrected, reference adde
Generalized Lagrangian of N = 1 supergravity and its canonical constraints with the real Ashtekar variable
We generalize the Lagrangian of N = 1 supergravity (SUGRA) by using an
arbitrary parameter , which corresponds to the inverse of Barbero's
parameter . This generalized Lagrangian involves the chiral one as a
special case of the value . We show that the generalized
Lagrangian gives the canonical formulation of N = 1 SUGRA with the real
Ashtekar variable after the 3+1 decomposition of spacetime. This canonical
formulation is also derived from those of the usual N = 1 SUGRA by performing
Barbero's type canonical transformation with an arbitrary parameter . We give some comments on the canonical formulation of the theory.Comment: 17 pages, LATE
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