35,680 research outputs found
Lagrange Model for the Chiral Optical Properties of Stereometamaterials
We employ a general Lagrange model to describe the chiral optical properties
of stereometamaterials. We derive the elliptical eigenstates of a twisted
stacked split-ring resonator, taking phase retardation into account. Through
this approach, we obtain a powerful Jones matrix formalism which can be used to
calculate the polarization rotation, ellipticity, and circular dichroism of
transmitted waves through stereometamaterials at any incident polarization. Our
experimental measurements agree well with our model.Comment: 10 pages, 3 figures, Theory and experimen
Fluctuations of Spatial Patterns as a Measure of Classical Chaos
In problems where the temporal evolution of a nonlinear system cannot be
followed, a method for studying the fluctuations of spatial patterns has been
developed. That method is applied to well-known problems in deterministic chaos
(the logistic map and the Lorenz model) to check its effectiveness in
characterizing the dynamical behaviors. It is found that the indices
are as useful as the Lyapunov exponents in providing a quantitative measure of
chaos.Comment: 10 pages + 7 figures (in ps file), LaTex, Submitted to Phys. Rev.
Numerical simulations of negative-index refraction in wedge-shaped metamaterials
A wedge-shaped structure made of split-ring resonators (SRR) and wires is
numerically simulated to evaluate its refraction behavior. Four frequency
bands, namely, the stop band, left-handed band, ultralow-index band, and
positive-index band, are distinguished according to the refracted field
distributions. Negative phase velocity inside the wedge is demonstrated in the
left-handed band and the Snell's law is conformed in terms of its refraction
behaviors in different frequency bands. Our results confirmed that negative
index of refraction indeed exists in such a composite metamaterial and also
provided a convincing support to the results of previous Snell's law
experiments.Comment: 18 pages, 6 figure
Competing Ground States in Triple-layered Sr4Ru3O10: Verging on Itinerant Ferromagnetism with Critical Fluctuations
Sr4Ru3O10 is characterized by a sharp metamagnetic transition and
ferromagnetic behavior occurring within the basal plane and along the c-axis,
respectively. Resistivity at magnetic field, B, exhibits low-frequency quantum
oscillations when B||c-axis and large magnetoresistivity accompanied by
critical fluctuations driven by the metamagnetism when B^c-axis. The complex
behavior evidenced in resistivity, magnetization and specific heat presented is
not characteristic of any obvious ground states, and points to an exotic state
that shows a delicate balance between fluctuations and order.Comment: 18 pages, 4 figure
Orientation and strain modulated electronic structures in puckered arsenene nanoribbons
Orthorhombic arsenene was recently predicted as an indirect bandgap
semiconductor. Here, we demonstrate that nanostructuring arsenene into
nanoribbons can successfully transform the bandgap to be direct. It is found
that direct bandgaps hold for narrow armchair but wide zigzag nanoribbons,
which is dominated by the competition between the in-plane and out-of-plane
bondings. Moreover, straining the nanoribbons also induces a direct bandgap and
simultaneously modulates effectively the transport property. The gap energy is
largely enhanced by applying tensile strains to the armchair structures. In the
zigzag ones, a tensile strain makes the effective mass of holes much higher
while a compressive strain cause it much lower than that of electrons. Our
results are crutial to understand and engineer the electronic properties of two
dimensional materials beyond the planar ones like graphene
Metal-to-insulator transition and magnetic ordering in CaRu_{1-x}Cu_xO_3
CaRuO_3 is perovskite with an orthorhombic distortion and is believed to be
close to magnetic ordering. Magnetic studies of single crystal and
polycrystalline CaRu_{1-x}Cu_xO_3 (0\le x \le 15 at.%Cu) reveal that
spin-glass-like transition develops for x\le 7 at.%Cu and obtained value for
effective magnetic moment p_{eff}=3.55 mu_B for x=5 at.% Cu, single crystal,
indicates presence of Ru^{5+}. At higher Cu concentrations more complex
magnetic behaviors are observed. Electrical resistivity measured on
polycrystalline samples shows metal-to-insulator transition (MIT) at 51 K for
only 2 at.% Cu. Charge compensation, which is assumed to be present upon
Cu^{2+/3+} substitution, induces appearance of Ru^{5+} and/or creation of
oxygen vacancies in crystal structure. Since the observed changes in physical
properties are completely attributable to the charge compensation, they cannot
be related to behaviors of pure compound where no such mechanism is present.
This study provides the criterion for "good" chemical probes for studying
Ru-based perovskites.Comment: 12 pages, 7 figure
Microscopic Study of the Isoscalar Giant Monopole Resonance in Cd, Sn and Pb Isotopes
The isoscalar giant monopole resonance (ISGMR) in Cd, Sn and Pb isotopes has
been studied within the self-consistent Skyrme Hartree-Fock+BCS and
quasi-particle random phase approximation (QRPA). Three Skyrme parameter sets
are used in the calculations, i.e., SLy5, SkM* and SkP, since they are
characterized by different values of the compression modulus in symmetric
nuclear matter, namely K=230, 217, and 202 MeV, respectively. We also
investigate the effect of different types of pairing forces on the ISGMR in Cd,
Sn and Pb isotopes. The calculated peak energies and the strength distributions
of ISGMR are compared with available experimental data. We find that SkP fails
completely to describe the ISGMR strength distribution for all isotopes due to
its low value of the nuclear matter incompressibility, namely K=202 MeV. On the
other hand, the SLy5 parameter set, supplemented by an appropriate pairing
interaction, gives a reasonable description of the ISGMR in Cd and Pb isotopes.
A better description of ISGMR in Sn isotopes is achieved by the SkM*
interaction, that has a somewhat softer value of the nuclear incompressibility.Comment: Submitted to Phys. Rev.
Topology in thermodynamics of regular black strings with Kaluza-Klein reduction
We study the topological defects in the thermodynamics of regular black
strings (from a four-dimensional perspective) that is symmetric under the
double Wick rotation and constructed in the high-dimensional spacetime with an
extra dimension compactified on a circle. We observe that the thermodynamic
phases of regular black strings can be topologically classified by the positive
and negative winding numbers (at the defects) which correspond to the
thermodynamically stable and unstable branches. This topological classification
implies a phase transition due to the decay of a thermodynamically unstable
regular black string to another which is thermodynamically stable. We confirm
these topological properties of the thermodynamics of regular black strings by
investigating their free energy, heat capacity, and Ruppeiner scalar curvature
of the state space. The Ruppeiner scalar curvature of regular black strings is
found to be always negative, implying that the interactions among the
microstructures of regular black strings are only attractive.Comment: 21 pages, 10 figure
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