3,465 research outputs found
SO(5) superconductor in a Zeeman magnetic field: Phase diagram and thermodynamic properties
In this paper we present calculations of the SO(5) quantum rotor theory of
high-T superconductivity in Zeeman magnetic field. We use the spherical
approach for five-component quantum rotors in three-dimensional lattice to
obtain formulas for critical lines, free energy, entropy and specific heat and
present temperature dependences of these quantities for different values of
magnetic field. Our results are in qualitative agreement with relevant
experiments on high-T cuprates.Comment: 4 pages, 2 figures, to appear in Phys. Rev. B, see http://prb.aps.or
Dependence of the superconducting critical temperature on the number of layers in homologous series of high-Tc cuprates
We study a model of -layer high-temperature cuprates of homologous series
like HgBa_2Ca_(n-1)Cu_nO_(2+2n+\delta) to explain the dependence of the
critical temperature Tc(n) on the number of Cu-O planes in the elementary
cell. Focusing on the description of the high-temperature superconducting
system in terms of the collective phase variables, we have considered a
semi-microscopic anisotropic three-dimensional vector XY model of stacked
copper-oxide layers with adjustable parameters representing microscopic
in-plane and out-of-plane phase stiffnesses. The model captures the layered
composition along c-axis of homologous series and goes beyond the
phenomenological Lawrence-Doniach model for layered superconductors.
Implementing the spherical closure relation for vector variables we have solved
the phase XY model exactly with the help of transfer matrix method and
calculated Tc(n) for arbitrary block size , elucidating the role of the
c-axis anisotropy and its influence on the critical temperature. Furthermore,
we accommodate inhomogeneous charge distribution among planes characterized by
the charge imbalance coefficient being the function of number of layers
. By making a physically justified assumption regarding the doping
dependence of the microscopic phase stiffnesses, we have calculated the values
of parameter as a function of block size in good agreement with the
nuclear magnetic resonance data of carrier distribution in multilayered high-Tc
cuprates.Comment: 15 pages, 10 figures. Submitted to Physical Review
Synthetic magnetic field effects on neutral bosonic condensates in quasi three-dimensional anisotropic layered structures
We discuss a system of dilute Bose gas confined in a layered structure of
stacked square lattices (slab geometry). A derived phase diagram reveals a
non-monotonic dependence of the ratio of tunneling to on-site repulsion on the
artificial magnetic field applied to the system. The effect is reduced when
more layers are added, which mimics a two- to quasi-three-dimensional geometry
crossover. Furthermore, we establish a correspondence between anisotropic
infinite (quasi three-dimensional) and isotropic finite (slab geometry) systems
that share exactly the same critical values, which can be an important clue for
choosing experimental setups that are less demanding, but still leading to the
identical results. Finally, we show that the properties of the ideal Bose gas
in a three-dimensional optical lattice can be closely mimicked by finite (slab)
systems, when the number of two-dimensional layers is larger than ten for
isotropic interactions or even less, when the layers are weakly coupled.Comment: http://pra.aps.org/abstract/PRA/v83/i2/e02360
Numerical Simulation of Superparamagnetic Nanoparticle Motion in Blood Vessels for Magnetic Drug Delivery
A numerical model is developed for the motion of superparamagnetic
nanoparticles in a non-Newtonian blood flow under the influence of a magnetic
field. The rheological properties of blood are modeled by the Carreau flow and
viscosity, and the stochastic effects of Brownian motion and red blood cell
collisions are considered. The model is validated with existing data and good
agreement with experimental results is shown. The effectiveness of magnetic
drug delivery in various blood vessels is assessed and found to be most
successful in arterioles and capillaries. A range of magnetic field strengths
are modeled using equations for both a bar magnet and a point dipole: it is
shown that the bar magnet is effective at capturing nanoparticles in limited
cases while the point dipole is highly effective across a range of conditions.
A parameter study is conducted to show the effects of changing the dipole
moment, the distance from the magnet to the blood vessel, and the initial
release point of the nanoparticles. The distance from the magnet to the blood
vessel is shown to play a significant role in determining nanoparticle capture
rate. The optimal initial release position is found to be located within the
tumor radius in capillaries and arterioles to prevent rapid diffusion to the
edges of the blood vessel prior to arriving at the tumor, and near the edge of
the magnet when a bar magnet is used.Comment: Fixed the title spacin
Superexchange Interaction in Insulating EuZnP
We report magnetic and transport properties of single-crystalline
EuZnP, which has trigonal CaAlSi-type crystal structure and
orders antiferromagnetically at 23~K. Easy -plane
magneto-crystalline anisotropy was confirmed from the magnetization isotherms,
measured with a magnetic field applied along different crystallographic
directions (-plane and -axis). Positive Curie-Weiss temperature
indicates dominating ferromagnetic correlations. Electrical resistivity
displays insulating behavior with a band-gap of 0.177~eV, which
decreases to 0.13~eV upon application of a high magnetic field. We
explained the intriguing presence of magnetic interactions in an intermetallic
insulator by the mechanism of extended superexchange, with phosphorus as an
anion mediator, which is further supported by our analysis of the charge and
spin density distributions. We constructed the effective Heisenberg model, with
exchange parameters derived from the \textit{ab initio} DFT calculations, and
employed it in Monte-Carlo simulations, which correctly reproduced the
experimental value of N\'eel temperature
Power-Law Behavior of Power Spectra in Low Prandtl Number Rayleigh-Benard Convection
The origin of the power-law decay measured in the power spectra of low
Prandtl number Rayleigh-Benard convection near the onset of chaos is addressed
using long time numerical simulations of the three-dimensional Boussinesq
equations in cylindrical domains. The power-law is found to arise from
quasi-discontinuous changes in the slope of the time series of the heat
transport associated with the nucleation of dislocation pairs and roll
pinch-off events. For larger frequencies, the power spectra decay exponentially
as expected for time continuous deterministic dynamics.Comment: (10 pages, 6 figures
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