19,043 research outputs found
Three Dimensional Topological Field Theory induced from Generalized Complex Structure
We construct a three-dimensional topological sigma model which is induced
from a generalized complex structure on a target generalized complex manifold.
This model is constructed from maps from a three-dimensional manifold to an
arbitrary generalized complex manifold . The theory is invariant under the
diffeomorphism on the world volume and the -transformation on the
generalized complex structure. Moreover the model is manifestly invariant under
the mirror symmetry. We derive from this model the Zucchini's two dimensional
topological sigma model with a generalized complex structure as a boundary
action on . As a special case, we obtain three dimensional
realization of a WZ-Poisson manifold.Comment: 18 page
Josephson Vortex States in Intermediate Fields
Motivated by recent resistance data in high superconductors in fields
{\it parallel} to the CuO layers, we address two issues on the Josephson-vortex
phase diagram, the appearances of structural transitions on the observed first
order transition (FOT) curve in intermediate fields and of a lower critical
point of the FOT line. It is found that some rotated pinned solids are more
stable than the ordinary rhombic pinned solids with vacant interlayer spacings
and that, due to the vertical portion in higher fields of the FOT line, the FOT
tends to be destroyed by creating a lower critical point.Comment: 12 pages, 3 figures. To appear in J.Phys.Soc.Jpn. 71, No.2 (February,
2002
Vortex tilt modulus in Fulde-Ferrell-Larkin-Ovchinnikov state
Vortex tilt response in Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) vortex
lattice is theoretically examined as a probe reflecting the spatial structure
of this state. In the FFLO state with nodal planes perpendicular to the
magnetic field in a quasi 2D material under a parallel field, the tilt modulus
E_{2} {\it of the nodal planes} decreases as the paramagnetic effect is
effectively enhanced, and this reduction of E_{2} in turn reduces the vortex
tilt modulus. This reduction of vortex tilt modulus, more remarkable in more
anisotropic systems, accompanying the FFLO transition may be an origin of the
monotonous reduction of sound velocity detected upon cooling in a ultrasound
measurement for CeCoIn5.Comment: 14 pages, 5 figures. Accepted for publication in Phys. Rev.
High field superconducting phase diagrams including Fulde-Ferrell-Larkin-Ovchinnikov vortex states
Motivated by a striking observation of a Fulde-Ferell-Larkin-Ovchinnikov
(FFLO) vortex state in the heavy fermion material CeCoIn5 in fields {\it
perpendicular} to the superconducting planes (),
superconducting phase diagrams including an FFLO state of quasi two-dimensional
(Q2D) superconductors are systematically studied. In the clean {\it limit}, the
high field superconducting state in the low temperature limit should be not the
FFLO state modulating along , appeared in CeCoIn5 in both and , but a different vortex state with a
modulation, induced by the paramagnetism, perpendicular to the field. It is
found that the presence of weak impurities is the origin of the absence in
CeCoIn5 of the latter state and leads to the phase
diagram, as seen in CeCoIn5, {\it apparently} different in character from that
in .Comment: A reference was updated. To appear in Phys. Rev.
Effect of in-plane line defects on field-tuned superconductor-insulator transition behavior in homogeneous thin film
Field-tuned superconductor-insulator transition (FSIT) behavior in 2D
isotropic and homogeneous thin films is usually accompanied by a nonvanishing
critical resistance at low . It is shown that, in a 2D film including line
defects paralle to each other but with random positions perpendicular to them,
the (apparent) critical resistance in low limit vanishes, as in the 1D
quantum superconducting (SC) transition, under a current parallel to the line
defects. This 1D-like critical resistive behavior is more clearly seen in
systems with weaker point disorder and may be useful in clarifying whether the
true origin of FSIT behavior in the parent superconductor is the glass
fluctuation or the quantum SC fluctuation. As a by-product of the present
calculation, it is also pointed out that, in 2D films with line-like defects
with a long but {\it finite} correlation length parallel to the lines, a
quantum metallic behavior intervening the insulating and SC ones appears in the
resistivity curves.Comment: 16 pages, 14 figure
Theoretical Description of Resistive Behavior near a Quantum Vortex-Glass Transition
Resistive behaviors at nonzero temperatures (T > 0) reflecting a quantum
vortex-glass (VG) transition (the so-called field-tuned
superconductor-insulator transition at T=0) are studied based on a quantum
Ginzburg-Landau (GL) action for a s-wave pairing case containing microscopic
details. The ordinary dissipative dynamics of the pair-field is assumed on the
basis of a consistency between the fluctuation conductance terms excluded from
GL approach and an observed negative magnetoresistance. It is shown that the VG
contribution, G_{vg}(B=B_{vg}, T \to 0),to 2D fluctuation conductance at the VG
transition field B_{vg} depends on the strength of a repulsive-interaction
between electrons and takes a universal value only in the ordinary dirty limit
neglecting the electron-repulsion. Available resistivity data near B_{vg} are
discussed based on our results, and extensions to the cases of a d-wave pairing
and of 3D systems are briefly commented on.Comment: Explanation of data in strongly disordered case, as well as Fig.2 and
3, was renewed, and comments on recent publications were added. To appear in
J.Phys.Soc. Jp
An Alternative Topological Field Theory of Generalized Complex Geometry
We propose a new topological field theory on generalized complex geometry in
two dimension using AKSZ formulation. Zucchini's model is model in the case
that the generalized complex structuredepends on only a symplectic structure.
Our new model is model in the case that the generalized complex structure
depends on only a complex structure.Comment: 29 pages, typos and references correcte
Saving and Interest Rates in Japan:Why They Have Fallen and Why They Will Remain Low
Saving, Heterogeneity, general equilibrium
Theoretical Description of Nearly Discontinuous Transition in Superconductors with Paramagnetic Depairing
Based on a theoretical argument and Monte Carlo simulations of a
Ginzburg-Landau model derived microscopically, it is argued that, in type-II
superconductors where {\it both} the paramagnetic {\it and} orbital depairings
are important, a strong first-order transition (FOT) at expected in
the mean field (MF) approximation never occurs in real systems and changes due
to the fluctuation into a crossover. The present result explains why a {\it
nearly} discontinuous crossover at with {\it no} intrinsic hysteresis
is observed only in a clean superconducting material with a singlet pairing and
a high condensation energy such as CeCoIn.Comment: Publication version. See cond-mat/0306060 regarding a corresponding
long pape
Microscopic Study of Quantum Vortex-Glass Transition Field in Two-Dimensional Superconductors
The position of a field-tuned superconductor-insulator quantum transition
occuring in disordered thin films is examined within the mean field
approximation. Our calculation shows that the microscopic disorder-induced
reduction of the quantum transition point found experimentally cannot be
explained if the interplay between the disorder and an electron-electron
repulsive interaction is ignored. This work is presented as a microscopic basis
of an explanation (cond-mat/0105122) of resistive phenomena near the transition
field.Comment: 16 pages, 5 figures. To appear in J.Phys.Soc.Jp
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