8,003 research outputs found
Superconductivity and Abelian Chiral Anomalies
Motivated by the geometric character of spin Hall conductance, the
topological invariants of generic superconductivity are discussed based on the
Bogoliuvov-de Gennes equation on lattices.
They are given by the Chern numbers of degenerate condensate bands for
unitary order, which are realizations of Abelian chiral anomalies for
non-Abelian connections. The three types of Chern numbers for the and
-directions are given by covering degrees of some doubled surfaces around
the Dirac monopoles. For nonunitary states, several topological invariants are
defined by analyzing the so-called -helicity. Topological origins of the
nodal structures of superconducting gaps are also discussed.Comment: An example with a figure and discussions are supplemente
Field-driven topological glass transition in a model flux line lattice
We show that the flux line lattice in a model layered HTSC becomes unstable
above a critical magnetic field with respect to a plastic deformation via
penetration of pairs of point-like disclination defects. The instability is
characterized by the competition between the elastic and the pinning energies
and is essentially assisted by softening of the lattice induced by a
dimensional crossover of the fluctuations as field increases. We confirm
through a computer simulation that this indeed may lead to a phase transition
from crystalline order at low fields to a topologically disordered phase at
higher fields. We propose that this mechanism provides a model of the low
temperature field--driven disordering transition observed in neutron
diffraction experiments on single crystals.Comment: 11 pages, 4 figures available upon request via snail mail from
[email protected]
Singular Density of States of Disordered Dirac Fermions in the Chiral Models
The Dirac fermion in the random chiral models is studied which includes the
random gauge field model and the random hopping model. We focus on a connection
between continuum and lattice models to give a clear perspective for the random
chiral models. Two distinct structures of density of states (DoS) around zero
energy, one is a power-law dependence on energy in the intermediate energy
range and the other is a diverging one at zero energy, are revealed by an
extensive numerical study for large systems up to . For the
random hopping model, our finding of the diverging DoS within very narrow
energy range reconciles previous inconsistencies between the lattice and the
continuum models.Comment: 4 pages, 4 figure
Topological Origin of Zero-Energy Edge States in Particle-Hole Symmetric Systems
A criterion to determine the existence of zero-energy edge states is
discussed for a class of particle-hole symmetric Hamiltonians. A ``loop'' in a
parameter space is assigned for each one-dimensional bulk Hamiltonian, and its
topological properties, combined with the chiral symmetry, play an essential
role. It provides a unified framework to discuss zero-energy edge modes for
several systems such as fully gapped superconductors, two-dimensional d-wave
superconductors, and graphite ribbons. A variants of the Peierls instability
caused by the presence of edges is also discussed.Comment: Completely rewritten. Discussions on coexistence of is- or
id_{xy}-wave order parameter near edges in d_{x^{2}-y^{2}}-wave
superconductors are added; 4 pages, 3 figure
Local structural disorder and superconductivity in KxFe2-ySe2
We report significantly enhanced magnetic moment in
K0.69(2)Fe1.45(1)Se2.00(1) single crystals with sharp Tc and bulk
superconductivity obtained by postannealing and quenching process. There are
two Fe sites in the K0.69(2)Fe1.45(1)Se2.00(1) unit cell: Fe1, which has higher
symmetry with longer average Fe-Se bond length, and Fe2, which has lower
symmetry with shorter average Fe-Se bond length. Temperature-dependent x-ray
absorption fine-structure (XAFS) analysis results on quenched and as-grown
K0.69(2)Fe1.45(1)Se2.00(1) crystals show that quenched
K0.69(2)Fe1.45(1)Se2.00(1) have increased average Fe-Se bond length and
decreased static disorder. Our results indicate that nonzero population of Fe1
sites is the key structural parameter that governs the bulk superconductivity.
We also show clear evidence that Fe1 sites carry higher magnetic moment than
Fe2 sites.Comment: 3 figures, 4 page
Entanglement Entropy of One-dimensional Gapped Spin Chains
We investigate the entanglement entropy (EE) of gapped S=1 and spin
chains with dimerization. We find that the effective boundary degrees of
freedom as edge states contribute significantly to the EE. For the
dimerized Heisenberg chain, the EE of the sufficiently long chain is
essentially explained by the localized effective spins on the
boundaries. As for S=1, the effective spins are also causing a Kennedy
triplet that yields a lower bound for the EE. In this case, the residual
entanglement reduces substantially by a continuous deformation of the
Heisenberg model to that of the AKLT Hamiltonian.Comment: 5 pages, 6 figure
The K2-ESPRINT Project VI: K2-105 b, a Hot-Neptune around a Metal-rich G-dwarf
We report on the confirmation that the candidate transits observed for the
star EPIC 211525389 are due to a short-period Neptune-sized planet. The host
star, located in K2 campaign field 5, is a metal-rich ([Fe/H] = 0.260.05)
G-dwarf (T_eff = 543070 K and log g = 4.480.09), based on
observations with the High Dispersion Spectrograph (HDS) on the Subaru 8.2m
telescope. High-spatial resolution AO imaging with HiCIAO on the Subaru
telescope excludes faint companions near the host star, and the false positive
probability of this target is found to be < using the open source
vespa code. A joint analysis of transit light curves from K2 and additional
ground-based multi-color transit photometry with MuSCAT on the Okayama 1.88m
telescope gives the orbital period of P = 8.2669020.000070 days and
consistent transit depths of or . The transit depth corresponds to a planetary radius of , indicating that EPIC 211525389 b is a
short-period Neptune-sized planet. Radial velocities of the host star, obtained
with the Subaru HDS, lead to a 3\sigma\ upper limit of 90 on the mass of EPIC 211525389 b, confirming its planetary nature.
We expect this planet, newly named K2-105 b, to be the subject of future
studies to characterize its mass, atmosphere, spin-orbit (mis)alignment, as
well as investigate the possibility of additional planets in the system.Comment: 11 pages, 9 figures, 4 tables, PASJ accepte
Holographic Renormalization of Foliation Preserving Gravity and Trace Anomaly
From the holographic renormalizationg group viewpoint, while the scale
transformation plays a primary role in the duality by providing the extra
dimension, the special conformal transformation seems to only play a secondary
role. We, however, claim that the space-time diffeomorphism is crucially
related to the latter. For its demonstration, we study the holographic
renormalization group flow of a foliation preserving diffeomophic theory of
gravity (a.k.a. space-time flipped Horava gravity). We find that the dual field
theory, if any, is only scale invariant but not conformal invariant. In
particular, we show that the holographic trace anomaly in four-dimension
predicts the Ricci scalar squared term that would be incompatible with the
Wess-Zumino consistency condition if it were conformal. This illustrates how
the foliation preserving diffeomophic theory of gravity could be inconsistent
with a theorem of the dual unitary quantum field theory.Comment: 18 pages, v2: reference added, v3: comments on more recent literature
added in response to referee's reques
Level-occupation switching of the Quantum Dot, and phase anomalies in mesoscopic interferometry
For a variety of quantum dots, the widths of different single-particle levels
may naturally differ by orders of magnitude. In particular, the width of one
strongly coupled level may be larger than the spacing between other, very
narrow, levels. We found that in this case many consecutive Coulomb blockade
peaks are due to occupation of the same broad level. Between the peaks the
electron jumps from this level to one of the narrow levels and the transmission
through the dot at the next resonance essentially repeats that at the previous
one. This offers a natural explanation of the salient features of the behavior
of the transmission phase in an interferometer with a QD. The theory of this
effect will be reviewed with special emphasis on the role of the interactions.
New results on the dot-charging measurements and the fine structure of
occupation switchings will be presented, accompanied by the unified description
of the whole series of CB peaks caused by a single broad level. We then discuss
the case where the system approaches the Kondo regime.Comment: 30 pages in IOP format, 11 figure
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