4,382 research outputs found
Phase diagram of the one-dimensional half-filled extended Hubbard model
We study the ground state of the one-dimensional half-filled Hubbard model
with on-site (nearest-neighbor) repulsive interaction () and
nearest-neighbor hopping . In order to obtain an accurate phase diagram, we
consider various physical quantities such as the charge gap, spin gap,
Luttinger-liquid exponents, and bond-order-wave (BOW) order parameter using the
density-matrix renormalization group technique. We confirm that the BOW phase
appears in a substantial region between the charge-density-wave (CDW) and
spin-density-wave phases. Each phase boundary is determined by multiple means
and it allows us to do a cross-check to demonstrate the validity of our
estimations. Thus, our results agree quantitatively with the renormalization
group results in the weak-coupling regime (), with the
perturbation results in the strong-coupling regime (), and with
the quantum Monte Carlo results in the intermediate-coupling regime. We also
find that the BOW-CDW transition changes from continuous to first order at the
tricritical point and the BOW
phase vanishes at the critical end point .Comment: 4 pages, 5 figure
Theory of Mott insulator/band insulator heterostructure
A theory of heterostructures comprised of LaTiO (a Mott insulator) and
SrTiO (a band insulator) is presented. The band structure of the Ti %
-electrons is treated with a nearest neighbor tight-binding approximation; the
electric fields arising from the La/Sr charge difference and the
carriers are treated within a Hartree approximation; and the on-site
interactions are treated by unrestricted Hartree-Fock. The phase diagram as a
function of interaction strength and layer number is determined and predictions
are made for optical conductivity experiments. A note worthy finding is that
the edges of the heterostructure are generally metallic.Comment: 11 pages, 9 figure
Wino Dark Matter in light of the AMS-02 2015 Data
The AMS-02 collaboration has recently reported the antiproton to proton ratio
with improved accuracy. In view of uncertainties of the production and the
propagation of the cosmic rays, the observed ratio is still consistent with the
secondary astrophysical antiproton to proton ratio. However, it is nonetheless
enticing to examine whether the observed spectrum can be explained by a
strongly motivated dark matter, the wino dark matter. As we will show, we find
that the antiproton flux from the wino annihilation can explain the observed
spectrum well for its mass range 2.5-3 TeV. The fit to data becomes
particularly well compared to the case without the annihilation for the thermal
wino dark matter case with a mass about 3 TeV. The ratio is predicted to be
quickly decreased at the energy several hundreds of GeV, if this possibility is
true, and it will be confirmed or ruled out in near future when the AMS-02
experiment accumulates enough data at this higher energy region.Comment: 6 pages, 2 figures, version accepted for publication in PRD (Rapid
Communication
Closed formula for the relative entropy of entanglement
The long-standing problem of finding a closed formula for the relative
entropy of entanglement (REE) for two qubits is addressed. A compact-form
solution to the inverse problem, which characterizes an entangled state for a
given closest separable state, is obtained. Analysis of the formula for a large
class of entangled states strongly suggests that a compact analytical solution
of the original problem, which corresponds to finding the closest separable
state for a given entangled state, can be given only in some special cases. A
few applications of the compact-form formula are given to show additivity of
the REE, to relate the REE with the Rains upper bound for distillable
entanglement, and to show that a Bell state does not have a unique closest
separable state.Comment: 7 pages, the title was modified as suggested by the PRA editor
Mass of Decaying Wino from AMS-02 2014
We revisit the decaying wino dark matter scenario in the light of the updated
positron fraction, electron and positron fluxes in cosmic ray recently reported
by the AMS-02 collaboration. We show the AMS-02 results favor the mass of the
wino dark matter at around a few TeV, which is consistent with the prediction
on the wino mass in the pure gravity mediation model.Comment: 10 pages, 1 figur
Hyperon-Quark Mixed Phase in Compact Stars
We investigate the properties of the hadron-quark mixed phase in compact
stars using a Brueckner-Hartree-Fock framework for hadronic matter and the MIT
bag model for quark matter. We find that the equation of state of the mixed
phase is similar to that given by the Maxwell construction. The composition of
the mixed phase, however, is very different from that of the Maxwell
construction; in particular, hyperons are completely suppressed.Comment: oral presentation at INPC 2007, Toky
Spin-dependent observables in surrogate reactions
Observables emitted from various spin states in compound U nuclei are
investigated to validate usefulness of the surrogate reaction method. It was
found that energy spectrum of cascading -rays and their multiplicities,
spectrum of evaporated neutrons, and mass-distribution of fission fragments
show clear dependence on the spin of decaying nuclei. The present results
indicate that they can be used to infer populated spin distributions which
significantly affect the decay branching ratio of the compound system produced
by the surrogate reactions
Charge ordering in \theta-(BEDT-TTF)2RbZn(SCN)4: Cooperative effects of electron correlations and lattice distortions
Combined effects of electron correlations and lattice distortions are
investigated on the charge ordering in \theta-(BEDT-TTF)2RbZn(SCN)4
theoretically in a two-dimensional 3/4-filled extended Hubbard model with
electron-lattice couplings. It is known that this material undergoes a phase
transition from a high-symmetry metallic state to a low-symmetry insulating
state with a horizontal-stripe charge order (CO) by lowering temperature. By
means of the exact-diagonalization method, we show that electron-phonon
interactions are crucial to stabilize the horizontal-stripe CO and to realize
the low-symmetry crystal structure.Comment: 7 peges, 7 figures, accepted for publication in Phys. Rev.
Electron-lattice coupling, orbital stability and the phase diagram of CaSrRuO
Hartree-Fock calculations are presented of a theoretical model describing the
Sr/CaRuO family of compounds. Both commensurate and incommensurate magnetic
states are considered, along with orbital ordering and the effect of lattice
distortions. For reasonable parameter values, interactions disfavor orbital
disproportionation. A coherent description of the observed phase diagram is
obtained.Comment: Changed content, and added a new referenc
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