960 research outputs found
Electronic Properties of Topological Materials: Optical Excitations in Moebius Conjugated Polymers
Electronic structures and optical excitations in Moebius conjugated polymers
are studied theoretically. Periodic and Moebius boundary conditions are applied
to the tight binding model of poly(para-phenylene), taking exciton effects into
account. We discuss that oligomers with a few structural units are more
effective than polymers for observations of effects of discrete wave numbers
that are shifted by the change in boundary condition. Next, calculations of
optical absorption spectra are reported. Certain components of optical
absorption for an electric field perpendicular to the polymer axis mix with
absorption spectra for an electric field parallel to the polymer axis.
Therefore, the polarization dependences of an electric field of light enable us
to detect whether conjugated polymers have the Moebius boundary.Comment: 10 pages, 6 figures, to be published in J. Phys. Soc. Jpn., Vol. 74
No. 2 (February, 2005), Letter sectio
Room-temperature ballistic transport in narrow graphene strips
We investigate electron-phonon couplings, scattering rates, and mean free
paths in zigzag-edge graphene strips with widths of the order of 10 nm. Our
calculations for these graphene nanostrips show both the expected similarity
with single-wall carbon nanotubes (SWNTs) and the suppression of the
electron-phonon scattering due to a Dirichlet boundary condition that prohibits
one major backscattering channel present in SWNTs. Low-energy acoustic phonon
scattering is exponentially small at room temperature due to the large phonon
wave vector required for backscattering. We find within our model that the
electron-phonon mean free path is proportional to the width of the nanostrip
and is approximately 70 m for an 11-nm-wide nanostrip.Comment: 5 pages and 5 figure
Strong coupling of the cyclotron motion of surface electrons on liquid helium to a microwave cavity
The strong coupling regime is observed in a system of two-dimensional electrons whose cyclotron motion is coupled to an electro-magnetic mode in a Fabry-Perot cavity resonator. The Rabi splitting of eigenfrequencies of coupled motion is observed both in the cavity reflection spectrum and ac current of electrons, the latter probed by measuring their bolometric photoresponse. Despite the fact that similar observations of the Rabi splitting in many-particle systems have been described as a quantum-mechanical effect, we show that the observed splitting can be explained completely by a model based on the classical electrodynamics
Phenomenology of the superconducting state in Sr2RuO4
The symmetry of the superconducting phase of Sr2RuO4 is identified as the
odd-parity pairing state d(k)=\hat{z}(k_x \pm i k_y) based on recent
experiments. The experimental evidence for the so-called orbital dependent
superconductivity leads to a single-band description of superconductivity based
on spin fluctuation mechanism. It is shown that the state \hat{z}(k_x \pm i
k_y) can be stabilized by the spin fluctuation feedback mechanism analogous to
the A-phase in 3He and by spin-orbit coupling effects.Comment: 7 pages, 1 figure, to be published in Proc. of the conference
"Anomalous Complex Superconductors" (Crete, 1998
Rates and determinants of antibiotics and probiotics prescription to children in Asia-Pacific countries
Antibiotic therapy may have important side effects. Guidelines recommend the administration of specific probiotics to reduce the risk of antibiotic-associated diarrhoea (AAD). The rates and determinants of antibiotics and co-prescription of probiotics in children remain poorly known in Asia-Pacific countries, which are very heterogenous in terms of economic development, health care organization and health policies. A survey among general practitioners (GPs) and paediatricians was performed in seven countries of the Asia-Pacific area (Australia, Japan, Indonesia, India, China, Singapore, and South Korea). Physicians completed an online questionnaire that explored their current habits and the determinants for prescribing antibiotics and probiotics. For the 731 physicians who completed the questionnaire (390 paediatricians and 341 GPs), 37% of all consultations for a child led to the prescription of antibiotics (ranging from 17% in Australia to 47% in India). A large majority of physicians (84%) agreed that antibiotics disrupted gut microbiota and considered probiotics an effective intervention to prevent AAD (68%). However, only 33% co-prescribed probiotics with antibiotics (ranging from 13% in Japan to 60% in South Korea). The main reasons for prescribing probiotics were previous episodes of AAD (61%), presence of diarrhoea (55%), prolonged antibiotic treatment (54%) or amoxicillin-clavulanic acid therapy (54%). Although current local guidelines recommend the use of selected probiotics in children receiving antibiotics in Asia-Pacific area, the rates of antibiotics and probiotics prescription significantly vary among countries and are deeply affected by country-related cultural and organisational issues
Spin triplet superconductivity with line nodes in Sr2RuO4
Several possible odd-parity states are listed up group-theoretically and
examined in light of recent experiments on SrRuO. Those include some of
the -wave pairing states, {\mib d}({\mib k})\propto{\hat{\mib z}}
k_xk_y(k_x + {\rm i}k_y) and {\hat{\mib z}} (k_x^2-k_y^2)(k_x + {\rm i}k_y)
and other {\hat{\mib z}} (k_x + {\rm i}k_y)\cos ck_z ( is the -axis
lattice constant) as most plausible candidates. These are time-reversal
symmetry broken states and have line nodes running either vertically (the
former two) or horizontally (the latter), consistent with experiments.
Characterizations of these states and other possibilities are given.Comment: 4 pages, no figure
Photogeneration Dynamics of a Soliton Pair in Polyacetylene
Dynamical process of the formation of a soliton pair from a photogenerated
electron-hole pair in polyacetylene is studied numerically by adopting the SSH
Hamiltonian. A weak local disorder is introduced in order to trigger the
formation. Starting from an initial configuration with an electron at the
bottom of the conduction band and a hole at the top of the valence band,
separated by the Peierls gap, the time dependent Schrndinger
equation for the electron wave functions and the equation of motion for the
lattice displacements are solved numerically. After several uniform
oscillations of the lattice system at the early stage, a large distortion
corresponding to a pair of a soliton and an anti-soliton develops from a point
which is determined by the location and type of the disorder. In some cases,
two solitons run in opposite directions, leaving breather like oscillations
behind, and in other cases they form a bound state emitting acoustic lattice
vibrational modes.Comment: 16 pages 7 figure
Tomography of pairing symmetry from magnetotunneling spectroscopy -- a case study for quasi-1D organic superconductors
We propose that anisotropic -, -, or -wave pairing symmetries can be
distinguished from a tunneling spectroscopy in the presence of magnetic fields,
which is exemplified here for a model organic superconductor .
The shape of the Fermi surface (quasi-one-dimensional in this example) affects
sensitively the pairing symmetry, which in turn affects the shape (U or V) of
the gap along with the presence/absence of the zero-bias peak in the tunneling
in a subtle manner. Yet, an application of a magnetic field enables us to
identify the symmetry, which is interpreted as an effect of the Doppler shift
in Andreev bound states.Comment: 4 papegs, 4 figure
Josephson Effect between Condensates with Different Internal Structures
A general formula for Josephson current in a wide class of hybrid junctions
between different internal structures is derived on the basis of the Andreev
picture. The formula extends existing formulae and also enables us to analyze
novel B-phase/A-phase/B-phase (BAB) junctions in superfluid helium three
systems, which are accessible to experiments. It is predicted that BAB
junctions will exhibit two types of current-phase relations associated with
different internal symmetries. A ``pseudo-magnetic interface effect'' inherent
in the system is also revealed.Comment: 4 pages, 2 figure
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