36,098 research outputs found
Multiferroicity in the frustrated spinel cuprate GeCuO
Different from other magnetically frustrated spinel systems,
GeCuO is a strongly tetragonal distorted spinel cuprate in which
edge-sharing CuO ribbons are running along alternating directions
perpendicular to the -axis. Here, GeCuO samples of high quality
were prepared via high pressure synthesis (at 4 GPa) and the corresponding
magnetic and dielectric properties were investigated. For the first time, we
observed a ferroelectric polarization emerging at T 33~K. Although
the ferroelectric polarization is weak in GeCuO (
0.2C/m), the existence of spin-induced multiferroicity provides a
strong constraint on the possible ground state magnetic structures and/or the
corresponding theoretical models of multiferroicity for GeCuO.Comment: https://journals.aps.org/prmaterials/abstract/10.1103/PhysRevMaterials.2.04140
Electron g-2 in Light-Front Quantization
Basis Light-front Quantization has been proposed as a nonperturbative
framework for solving quantum field theory. We apply this approach to Quantum
Electrodynamics and explicitly solve for the light-front wave function of a
physical electron. Based on the resulting light-front wave function, we
evaluate the electron anomalous magnetic moment. Nonperturbative mass
renormalization is performed. Upon extrapolation to the infinite basis limit
our numerical results agree with the Schwinger result obtained in perturbation
theory to an accuracy of 0.06%.Comment: 6 pages, 4 figure
Quantum Phase Transition, O(3) Universality Class and Phase Diagram of Spin-1/2 Heisenberg Antiferromagnet on Distorted Honeycomb Lattice: A Tensor Renormalization Group Study
The spin-1/2 Heisenberg antiferromagnet on the distorted honeycomb (DHC)
lattice is studied by means of the tensor renormalization group method. It is
unveiled that the system has a quantum phase transition of second-order between
the gapped quantum dimer phase and a collinear Neel phase at the critical point
of coupling ratio \alpha_{c} = 0.54, where the quantum critical exponents \nu =
0.69(2) and \gamma = 1.363(8) are obtained. The quantum criticality is found to
fall into the O(3) universality class. A ground-state phase diagram in the
field-coupling ratio plane is proposed, where the phases such as the dimer,
semi-classical Neel, and polarized phases are identified. A link between the
present spin system to the boson Hubbard model on the DHC lattice is also
discussed.Comment: 6 pages, 5 figures, published in Phys. Rev.
The Density Profile of Cluster-scale Dark Matter Halos
We measure the average gravitational shear profile of 6 massive clusters
(M_vir ~ 10^15 M_sun) at z=0.3 out to a radius ~2h^-1 Mpc. The measurements are
fitted to a generalized NFW-like halo model \rho(r) with an arbitrary r -> 0
slope \alpha. The data are well fitted by such a model with a central cusp with
\alpha ~ 0.9 - 1.6 (68% confidence interval). For the standard-NFW case \alpha
= 1.0, we find a concentration parameter c_vir that is consistent with recent
predictions from high-resolution CDM N-body simulations. Our data are also well
fitted by an isothermal sphere model with a softened core. For this model, our
1\sigma upper limit for the core radius corresponds to a limit \sigma_star \leq
0.1 cm^2 g^-1 on the elastic collision cross-section in a self-interacting dark
matter model.Comment: 4 pages, 3 figures; version accepted for publication by ApJ Letters.
Three figures omitted to allow space for new fig. 3 and expanded results and
discussion sections, including NSIS model fi
Evolution of magnetic component in Yang-Mills condensate dark energy models
The evolution of the electric and magnetic components in an effective
Yang-Mills condensate dark energy model is investigated. If the electric field
is dominant, the magnetic component disappears with the expansion of the
Universe. The total YM condensate tracks the radiation in the earlier Universe,
and later it becomes thus is similar to the cosmological constant.
So the cosmic coincidence problem can be avoided in this model. However, if the
magnetic field is dominant, holds for all time, suggesting that it
cannot be a candidate for the dark energy in this case.Comment: 12 pages, 4 figures, minor typos correcte
Detecting relic gravitational waves in the CMB: A statistical bias
Analyzing the imprint of relic gravitational waves (RGWs) on the cosmic
microwave background (CMB) power spectra provides a way to determine the signal
of RGWs. In this Letter, we discuss a statistical bias, which could exist in
the data analysis and has the tendency to overlook the RGWs. We also explain
why this bias exists, and how to avoid it.Comment: 4 pages, 1 figur
An exact equilibrium reduced density matrix formulation I: The influence of noise, disorder, and temperature on localization in excitonic systems
An exact method to compute the entire equilibrium reduced density matrix for
systems characterized by a system-bath Hamiltonian is presented. The approach
is based upon a stochastic unraveling of the influence functional that appears
in the imaginary time path integral formalism of quantum statistical mechanics.
This method is then applied to study the effects of thermal noise, static
disorder, and temperature on the coherence length in excitonic systems. As
representative examples of biased and unbiased systems, attention is focused on
the well-characterized light harvesting complexes of FMO and LH2, respectively.
Due to the bias, FMO is completely localized in the site basis at low
temperatures, whereas LH2 is completely delocalized. In the latter, the
presence of static disorder leads to a plateau in the coherence length at low
temperature that becomes increasingly pronounced with increasing strength of
the disorder. The introduction of noise, however, precludes this effect. In
biased systems, it is shown that the environment may increase the coherence
length, but only decrease that of unbiased systems. Finally it is emphasized
that for typical values of the environmental parameters in light harvesting
systems, the system and bath are entangled at equilibrium in the single
excitation manifold. That is, the density matrix cannot be described as a
product state as is often assumed, even at room temperature. The reduced
density matrix of LH2 is shown to be in precise agreement with the steady state
limit of previous exact quantum dynamics calculations.Comment: 37 pages, 12 figures. To appear in Phys. Rev.
- …