10,040 research outputs found
Angle Dependence of Landau Level Spectrum in Twisted Bilayer Graphene
In the context of the low energy effective theory, the exact Landau level
spectrum of quasiparticles in twisted bilayer graphene with small twist angle
is analytically obtained by spheroidal eigenvalues. We analyze the dependence
of the Landau levels on the twist angle to find the points, where the two-fold
degeneracy for twist angles is lifted in the nonzero modes and below/above
which massive/massless fermion pictures become valid. In the perpendicular
magnetic field of 10\,T, the degeneracy is removed at %angles around 3 degrees for a few low levels, specifically,
for the first pair of nonzero levels and
for the next pair. Massive quasiparticle
appears at in 10\,T, %angles less
than 1.17 degrees. which match perfectly with the recent experimental results.
Since our analysis is applicable to the cases of arbitrary constant magnetic
fields, we make predictions for the same experiment performed in arbitrary
constant magnetic fields, e.g., for B=40\,T we get and the sequence of angles for the pairs of nonzero energy levels. The symmetry restoration
mechanism behind the massive/massless transition is conjectured to be a
tunneling (instanton) in momentum space.Comment: 8 pages, 7 figures, version to appear in PR
Empirical distributions of galactic spin parameters from the SDSS
Using simple dimensional arguments for both spiral and elliptical galaxies,
we present formulas to derive an estimate of the halo spin parameter
for any real galaxy, in terms of common observational parameters. This allows a
rough estimate of , which we apply to a large volume limited sample of
galaxies taken from the SDSS data base. The large numbers involved (11,597)
allow the derivation of reliable distributions, as signal adds up
significantly in spite of the errors in the inferences for particular galaxies.
We find that if the observed distribution of is modeled with a
log-normal function, as often done for this distribution in dark matter halos
that appear in cosmological simulations, we obtain parameters and , interestingly consistent with
values derived from simulations. For spirals, we find a good correlation
between empirical values of and visually assigned Hubble types,
highlighting the potential of this physical parameter as an objective
classification tool.Comment: 8 pages, 6 figures, expanded final version, MNRAS (in press
Intrusion Prevention And Detection in Small to Medium-Sized Enterprises
This paper will examine in depth the reluctance of small to medium-sized enterprises (SMEs) to implement cybersecurity measures amidst the growing threat of cyberattacks. Small businesses encompass the vast majority of for profit and nonprofit organizations in the world. Due to the growing connectedness of the global economy through the Internet and e-business, the reluctance of SMEs to invest in security measures threatens the very existence of many organizations and their partners. The detection and defense against attacks through intrusion detection systems (IDS) and intrusion prevention systems (IPS) are two solutions that assist in detecting and deflecting potential breaches of security. An extensive look at how both IDS and IPS can provide meaningful solutions to SMEs through their visibility and control measures (including their unique characteristics, applications, and limitations) will be explored
Superconducting transition of a two-dimensional Josephson junction array in weak magnetic fields
The superconducting transition of a two-dimensional (2D) Josephson junction
array exposed to weak magnetic fields has been studied experimentally.
Resistance measurements reveal a superconducting-resistive phase boundary in
serious disagreement with the theoretical and numerical expectations. Critical
scaling analyses of the characteristics indicate contrary to the
expectations that the superconducting-to-resistive transition in weak magnetic
fields is associated with a melting transition of magnetic-field-induced
vortices directly from a pinned-solid phase to a liquid phase. The expected
depinning transition of vortices from a pinned-solid phase to an intermediate
floating-solid phase was not observed. We discuss effects of the
disorder-induced random pinning potential on phase transitions of vortices in a
2D Josephson junction array.Comment: 9 pages, 7 figures (EPS+JPG format), RevTeX
X-ray induced electronic structure change in CuIrS
The electronic structure of CuIrS has been investigated using various
bulk-sensitive x-ray spectroscopic methods near the Ir -edge: resonant
inelastic x-ray scattering (RIXS), x-ray absorption spectroscopy in the partial
fluorescence yield (PFY-XAS) mode, and resonant x-ray emission spectroscopy
(RXES). A strong RIXS signal (0.75 eV) resulting from a charge-density-wave gap
opening is observed below the metal-insulator transition temperature of 230 K.
The resultant modification of electronic structure is consistent with the
density functional theory prediction. In the spin- and charge- dimer disordered
phase induced by x-ray irradiation below 50 K, we find that a broad peak around
0.4 eV appears in the RIXS spectrum.Comment: 4 pages and 4 figure
Criterion for transformation of transverse domain wall to vortex or antivortex wall in soft magnetic thin-film nanostripes
We report on the criterion for the dynamic transformation of the internal
structure of moving domain walls (DWs) in soft magnetic thin-film nanostripes
above the Walker threshold field, Hw. In order for the process of
transformation from transverse wall (TW) to vortex wall (VW) or antivortex wall
(AVW) occurs, the edge-soliton core of the TW-type DW should grow sufficiently
to the full width at half maximum of the out-of-plane magnetizations of the
core area of the stabilized vortex (or antivortex) by moving inward along the
transverse (width) direction. Upon completion of the nucleation of the vortex
(antivortex) core, the VW (AVW) is stabilized, and then its core accompanies
the gyrotropic motion in a potential well (hill) of a given nanostripe. Field
strengths exceeding the Hw, which is the onset field of DW velocity breakdown,
are not sufficient but necessary conditions for dynamic DW transformation
Higgs Structures of Dyonic Instantons
We study Higgs field configurations of dyonic instantons in spontaneously
broken (4+1)-dimensional Yang-Mills theory. The adjoint scalar field solutions
to the covariant Laplace equation in the ADHM instanton background are
constructed in general noncanonical basis, and they are used to study
explicitly the Higgs field configurations of dyonic instantons when the gauge
fields are taken by Jackiw-Nohl-Rebbi instanton solutions. For these solutions
corresponding to small instanton number we then consider in some detail the
zero locus of the Higgs field, which describes the cross section of supertubes
connecting parallel D4-branes in string theory. Also the information on the
Higgs zeroes is used to discuss the residual gauge freedom concerning the
Jackiw-Nohl-Rebbi solutions.Comment: 1+27 pages, 6 figure
In-situ fabrication of cobalt-doped SrFe2As2 thin films by using pulsed laser deposition with excimer laser
The remarkably high superconducting transition temperature and upper critical
field of iron(Fe)-based layered superconductors, despite ferromagnetic material
base, open the prospect for superconducting electronics. However, success in
superconducting electronics has been limited because of difficulties in
fabricating high-quality thin films. We report the growth of high-quality
c-axis-oriented cobalt(Co)-doped SrFe2As2 thin films with bulk
superconductivity by using an in-situ pulsed laser deposition technique with a
248-nm-wavelength KrF excimer laser and an arsenic(As)-rich phase target. The
temperature and field dependences of the magnetization showing strong
diamagnetism and transport critical current density with superior Jc-H
performance are reported. These results provide necessary information for
practical applications of Fe-based superconductors.Comment: 8 pages, 3figures. to be published at Appl. Phys. Let
Resonant inelastic x-ray scattering study of holon-antiholon continuum in SrCuO2
We report a resonant inelastic x-ray scattering study of charge excitations
in the quasi-one-dimensional Mott insulator SrCuO2. We observe a continuum of
low-energy excitations, in which a highly dispersive feature with a large
sinusoidal dispersion (~1.1 eV) resides. We have also measured the optical
conductivity, and studied the dynamic response of the extended Hubbard model
with realistic parameters, using a dynamical density-matrix renormalization
group method. In contrast to earlier work, we do not find a long-lived exciton,
but rather these results suggest that the excitation spectrum comprises a
holon-antiholon continuum together with a broad resonance.Comment: Final version to be published in Phys. Rev. Let
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