27,822 research outputs found
Stability and Hermitian-Einstein metrics for vector bundles on framed manifolds
We adapt the notions of stability of holomorphic vector bundles in the sense
of Mumford-Takemoto and Hermitian-Einstein metrics in holomorphic vector
bundles for canonically polarized framed manifolds, i.e. compact complex
manifolds X together with a smooth divisor D such that K_X \otimes [D] is
ample. It turns out that the degree of a torsion-free coherent sheaf on X with
respect to the polarization K_X \otimes [D] coincides with the degree with
respect to the complete K\"ahler-Einstein metric g_{X \setminus D} on X
\setminus D. For stable holomorphic vector bundles, we prove the existence of a
Hermitian-Einstein metric with respect to g_{X \setminus D} and also the
uniqueness in an adapted sense.Comment: 21 pages, International Journal of Mathematics (to appear
Fano Resonance in a Quantum Wire with a Side-coupled Quantum Dot
We report a transport experiment on the Fano effect in a quantum connecting
wire (QW) with a side-coupled quantum dot (QD). The Fano resonance occurs
between the QD and the "T-shaped" junction in the wire, and the transport
detects anti-resonance or forward scattered part of the wavefunction. While in
this geometry it is more difficult to tune the shape of the resonance than in
the previously reported Aharonov-Bohm-ring type interferometer, the resonance
purely consists of the coherent part of transport. By utilizing this advantage,
we have qualitatively explained the temperature dependence of the Fano effect
by including the thermal broadening and the decoherence. We have also proven
that this geometry can be a useful interferometer to measure the phase
evolution of electrons at a QD.Comment: REVTEX, 6 pages including 5 figures, final versio
Novel electronic wave interference patterns in nanographene sheets
Superperiodic patterns with a long distance in a nanographene sheet observed
by STM are discussed in terms of the interference of electronic wave functions.
The period and the amplitude of the oscillations decrease spatially in one
direction. We explain the superperiodic patterns with a static linear potential
theoretically. In the k-p model, the oscillation period decreases, and agrees
with experiments. The spatial difference of the static potential is estimated
as 1.3 eV for 200 nm in distance, and this value seems to be reasonable in
order that the potential difference remains against perturbations, for example,
by phonon fluctuations and impurity scatterings. It turns out that the
long-distance oscillations come from the band structure of the two-dimensional
graphene sheet.Comment: Published as a LETTER in J. Phys.: Condens. Matter; 8 pages; 6
figures; Online version at
http://www.iop.org/EJ/S/3/1256/0hJAmc5sCL6d.7sOO.BtLw/abstract/0953-8984/14/3
6/10
Robust half-metallic antiferromagnets LaVOsO and LaMoO ( = Ca, Sr, Ba; = Re, Tc) from first-principles calculations
We have theoretically designed three families of the half-metallic (HM)
antiferromagnets (AFM), namely, LaVOsO, LaMoTcO and
LaMoReO ( = Ca, Sr, Ba), based on a systematic {\it ab initio} study
of the ordered double perovskites LaO with the possible and
pairs from all the 3, 4 and 5 transtion metal elements being
considered. Electronic structure calculations based on first-principles
density-functional theory with generalized gradient approximation (GGA) for
more than sixty double perovskites LaCaO have been performed using the
all-electron full-potential linearized augmented-plane-wave method. The found
HM-AFM state in these materials survives the full {\it ab initio} lattice
constant and atomic position optimizations which were carried out using
frozen-core full potential projector augmented wave method. It is found that
the HM-AFM properties predicted previously in some of the double perovskites
would disappear after the full structural optimizations. The AFM is attributed
to both the superexchange mechanism and the generalized double exchange
mechanism via the () - O (2) - () coupling
and the latter is also believed to be the origin of the HM. Finally, in our
search for the HM-AFMs, we find LaCrTcO and LaCrReO to be AFM
insulators of an unconventional type in the sense that the two
antiferromagnetic coupled ions consist of two different elements and that the
two spin-resolved densities of states are no longer the same.Comment: To appear in Phys. Rev.
Quasinormal modes of black holes localized on the Randall-Sundrum 2-brane
We investigate conformal scalar, electromagnetic, and massless Dirac
quasinormal modes of a brane-localized black hole. The background solution is
the four-dimensional black hole on a 2-brane that has been constructed by
Emparan, Horowitz, and Myers in the context of a lower dimensional version of
the Randall-Sundrum model. The conformally transformed metric admits a Killing
tensor, allowing us to obtain separable field equations. We find that the
radial equations take the same form as in the four-dimensional "braneless"
Schwarzschild black hole. The angular equations are, however, different from
the standard ones, leading to a different prediction for quasinormal
frequencies.Comment: 10 pages, 7 figures; references added, version to appear in PR
A New Linear Logic for Deadlock-Free Session-Typed Processes
The π -calculus, viewed as a core concurrent programming language, has been used as the target of much research on type systems for concurrency. In this paper we propose a new type system for deadlock-free session-typed π -calculus processes, by integrating two separate lines of work. The first is the propositions-as-types approach by Caires and Pfenning, which provides a linear logic foundation for session types and guarantees deadlock-freedom by forbidding cyclic process connections. The second is Kobayashi’s approach in which types are annotated with priorities so that the type system can check whether or not processes contain genuine cyclic dependencies between communication operations. We combine these two techniques for the first time, and define a new and more expressive variant of classical linear logic with a proof assignment that gives a session type system with Kobayashi-style priorities. This can be seen in three ways: (i) as a new linear logic in which cyclic structures can be derived and a CYCLE -elimination theorem generalises CUT -elimination; (ii) as a logically-based session type system, which is more expressive than Caires and Pfenning’s; (iii) as a logical foundation for Kobayashi’s system, bringing it into the sphere of the propositions-as-types paradigm
59Co-NMR Knight Shift of Superconducting Three-Layer NaxCoO2.yH2O
The superconducting state of NaxCoO2.yH2O with three CoO2 layers in a unit
cell has been studied by 59Co-NMR. The Knight shift measured for a peak of the
NMR spectra corresponding to the external magnetic field H along one of the
principal directions within the CoO2 plane, exhibits a rapid decrease with
decreasing temperature T below the superconducting transition temperature Tc,
indicating that the spin susceptibility is suppressed in the superconducting
phase, at least, for this field direction. Because differences of the
superconducting properties are rather small between this three-layer
NaxCoO2.yH2O and previously reported NaxCoO2.yH2O with two CoO2 layers within a
unit cell, the present result of the Knight shift studies indicates that the
Cooper pairs of the former system are in the singlet state as in the latter,
for which the spin susceptibility is suppressed for both directions of H
parallel and perpendicular to the CoO2 plane.Comment: 5 page
Superconductivity in an organic insulator at very high magnetic fields
We investigate by electrical transport the field-induced superconducting
state (FISC) in the organic conductor -(BETS)FeCl. Below 4 K,
antiferromagnetic-insulator, metallic, and eventually superconducting (FISC)
ground states are observed with increasing in-plane magnetic field. The FISC
state survives between 18 and 41 T, and can be interpreted in terms of the
Jaccarino-Peter effect, where the external magnetic field {\em compensates} the
exchange field of aligned Fe ions. We further argue that the Fe
moments are essential to stabilize the resulting singlet, two-dimensional
superconducting stateComment: 9 pages 3 figure
Te 5p orbitals bring three-dimensional electronic structure to two-dimensional Ir0.95Pt0.05Te2
We have studied the nature of the three-dimensional multi-band electronic
structure in the twodimensional triangular lattice Ir1-xPtxTe2 (x=0.05)
superconductor using angle-resolved photoemission spectroscopy (ARPES), x-ray
photoemission spectroscopy (XPS) and band structure calculation. ARPES results
clearly show a cylindrical (almost two-dimensional) Fermi surface around the
zone center. Near the zone boundary, the cylindrical Fermi surface is truncated
into several pieces in a complicated manner with strong three-dimensionality.
The XPS result and the band structure calculation indicate that the strong Te
5p-Te 5p hybridization between the IrTe2 triangular lattice layers is
responsible for the three-dimensionality of the Fermi surfaces and the
intervening of the Fermi surfaces observed by ARPES.Comment: 5 pages, 4 figure
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