10,425 research outputs found
Berezinskii-Kosterlitz-Thouless transitions in the six-state clock model
Classical 2D clock model is known to have a critical phase with
Berezinskii-Kosterlitz-Thouless(BKT) transitions. These transitions have
logarithmic corrections which make numerical analysis difficult. In order to
resolve this difficulty, one of the authors has proposed the method called
level spectroscopy, which is based on the conformal field theory. We extend
this method to the multi-degenerated case. As an example, we study the
classical 2D 6-clock model which can be mapped to the quantum self-dual 1D
6-clock model. Additionally, we confirm that the self-dual point has a precise
numerical agreement with the analytical result, and we argue the degeneracy of
the excitation states at the self-dual point from the effective field
theoretical point of view.Comment: 18pages, 7figure
Magnetization Plateau of an S=1 Frustrated Spin Ladder
We study the magnetization plateau at 1/4 of the saturation magnetization of
the S=1 antiferromagnetic spin ladder both analytically and numerically, with
the aim of explaining recent experimental results on BIP-TENO by Goto et al. We
propose two mechanisms for the plateau formation and clarify the plateau phase
diagram on the plane of the coupling constants between spins
Shape evolution and the role of intruder configurations in Hg isotopes within the interacting boson model based on a Gogny energy density functional
The interacting boson model with configuration mixing, with parameters
derived from the self-consistent mean-field calculation employing the
microscopic Gogny energy density functional, is applied to the systematic
analysis of the low-lying structure in Hg isotopes. Excitation energies,
electromagnetic transition rates, deformation properties, and ground-state
properties of the Hg nuclei are obtained by mapping the microscopic
deformation energy surface onto the equivalent IBM Hamiltonian in the boson
condensate. These results point to the overall systematic trend of the
transition from the near spherical vibrational state in lower-mass Hg nuclei
close to Hg, onset of intruder prolate configuration as well as the
manifest prolate-oblate shape coexistence around the mid-shell nucleus
Hg, weakly oblate deformed structure beyond Hg up to the
spherical vibrational structure toward the near semi-magic nucleus Hg,
as observed experimentally. The quality of the present method in the
description of the complex shape dynamics in Hg isotopes is examined.Comment: 19 pages, 14 figures, revised version including new results and
discussions, title changed, accepted for publication in Phys. Rev.
Structural evolution in germanium and selenium nuclei within the mapped interacting boson model based on the Gogny energy density functional
The shape transitions and shape coexistence in the Ge and Se isotopes are
studied within the interacting boson model (IBM) with the microscopic input
from the self-consistent mean-field calculation based on the Gogny-D1M energy
density functional. The mean-field energy surface as a function of the
quadrupole shape variables and , obtained from the constrained
Hartree-Fock-Bogoliubov method, is mapped onto the expectation value of the IBM
Hamiltonian with configuration mixing in the boson condensate state. The
resultant Hamiltonian is used to compute excitation energies and
electromagnetic properties of the selected nuclei Ge and
Se. Our calculation suggests that many nuclei exhibit
softness. Coexistence between prolate and oblate, as well as between spherical
and -soft, shapes is also observed. The method provides a reasonable
description of the observed systematics of the excitation energy of the
low-lying energy levels and transition strengths for nuclei below the neutron
shell closure , and provides predictions on the spectroscopy of
neutron-rich Ge and Se isotopes with , where data are scarce
or not available.Comment: 16 pages, 20 figure
Spectroscopy of quadrupole and octupole states in rare-earth nuclei from a Gogny force
Collective quadrupole and octupole states are described in a series of Sm and
Gd isotopes within the framework of the interacting boson model (IBM), whose
Hamiltonian parameters are deduced from mean field calculations with the Gogny
energy density functional. The link between both frameworks is the
() potential energy surface computed within the
Hartree-Fock-Bogoliubov framework in the case of the Gogny force. The
diagonalization of the IBM Hamiltonian provides excitation energies and
transition strengths of an assorted set of states including both positive and
negative parity states. The resultant spectroscopic properties are compared
with the available experimental data and also with the results of the
configuration mixing calculations with the Gogny force within the generator
coordinate method (GCM). The structure of excited states and its
connection with double octupole phonons is also addressed. The model is shown
to describe the empirical trend of the low-energy quadrupole and octupole
collective structure fairly well, and turns out to be consistent with GCM
results obtained with the Gogny force.Comment: 17 pages, 12 figures, 4 table
Coupled charge and valley excitations in graphene quantum Hall ferromagnets
Graphene is a two-dimensional carbon material with a honeycomb lattice and
Dirac-type low-energy spectrum. In a strong magnetic field, where Coulomb
interactions dominate against disorder broadening, quantum Hall ferromagnetic
states realize at integer fillings. Extending the quantum Hall ferromagnetism
to the fractional filling case of massless Dirac fermions, we study the
elementally charge excitations which couple with the valley degrees of freedom
(so-called valley skyrmions). With the use of the density matrix renomalization
group (DMRG) method, the excitation gaps are calculated and extrapolated to the
thermodynamic limit. These results exhibit numerical evidences and criterions
of the skyrmion excitations in graphene.Comment: 5 pages, 5 figure
Field-Induced gap due to four-spin exchange in a spin ladder
The effect of the four-spin cyclic exchange interaction at each plaquette in
the two-leg spin ladder is investigated at T=0, especially focusing on
the field-induced gap. The strong rung coupling approximation suggests that it
yields a plateau at half of the saturation moment () in the
magnetization curve, which corresponds to a field-induced spin gap with a
spontaneous breaking of the translational symmetry. A precise phase diagram at
is also presented based on the level spectroscopy analysis of the
numerical data obtained by Lanczos method. The boundary between the gapless and
plateau phases is confirmed to be of the Kosterlitz-Thouless (KT) universality
class.Comment: 10 pages, 3 eps figures (embedded), to be published in J. Phys.:
Cond. Matte
Ground state of an distorted diamond chain - model of
We study the ground state of the model Hamiltonian of the trimerized
quantum Heisenberg chain in which
the non-magnetic ground state is observed recently. This model consists of
stacked trimers and has three kinds of coupling constants between spins; the
intra-trimer coupling constant and the inter-trimer coupling constants
and . All of these constants are assumed to be antiferromagnetic. By
use of the analytical method and physical considerations, we show that there
are three phases on the plane (, ), the dimer phase, the spin fluid phase
and the ferrimagnetic phase. The dimer phase is caused by the frustration
effect. In the dimer phase, there exists the excitation gap between the
two-fold degenerate ground state and the first excited state, which explains
the non-magnetic ground state observed in . We also obtain the phase diagram on the
plane from the numerical diagonalization data for finite systems by use of the
Lanczos algorithm.Comment: LaTeX2e, 15 pages, 21 eps figures, typos corrected, slightly detailed
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