12,635 research outputs found
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
Universal Irreversibility of Normal Quantum Diffusion
Time-reversibility measured by the deviation of the perturbed time-reversed
motion from the unperturbed one is examined for normal quantum diffusion
exhibited by four classes of quantum maps with contrastive physical nature.
Irrespective of the systems, there exist a universal minimal quantum threshold
above which the system completely loses the past memory, and the time-reversed
dynamics as well as the time-reversal characteristics asymptotically trace
universal curves independent of the details of the systems.Comment: 4 pages, 4 figure
Thermal fluctuations and disorder effects in vortex lattices
We calculate using loop expansion the effect of fluctuations on the structure
function and magnetization of the vortex lattice and compare it with existing
MC results. In addition to renormalization of the height of the Bragg peaks of
the structure function, there appears a characteristic saddle shape ''halos''
around the peaks. The effect of disorder on magnetization is also calculated.
All the infrared divergencies related to soft shear cancel.Comment: 10 pages, revtex file, one figur
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
Elastic Instabilities within Antiferromagnetically Ordered Phase in the Orbitally-Frustrated Spinel GeCoO
Ultrasound velocity measurements of the orbitally-frustrated GeCoO
reveal unusual elastic instabilities due to the phonon-spin coupling within the
antiferromagnetic phase. Shear moduli exhibit anomalies arising from the
coupling to short-range ferromagnetic excitations. Diplike anomalies in the
magnetic-field dependence of elastic moduli reveal magnetic-field-induced
orbital order-order transitions. These results strongly suggest the presence of
geometrical orbital frustration which causes novel orbital phenomena within the
antiferromagnetic phase.Comment: 5 pages, 3 figure
Effect of the tensor force in the exchange channel on the spin-orbit splitting in 23F in the Hartree-Fock framework
We study the spin-orbit splitting (-splitting) for the proton d-orbits in
23F in the Hartree-Fock framework with the tensor force in the exchange
channel. 23F has one more proton around the neutron-rich nucleus 22O. A recent
experiment indicates that the ls-splitting for the proton d-orbits in 23F is
reduced from that in 17F. Our calculation shows that the ls-splitting in 23F
becomes smaller by about a few MeV due to the tensor force. This effect comes
from the interaction between the valence proton and the occupied neutrons in
the 0d5/2 orbit through the tensor force and makes the ls-splitting in 23F
close to the experimental data
Estimates on Green functions of second order differential operators with singular coefficients
We investigate the Green functions G(x,x^{\prime}) of some second order
differential operators on R^{d+1} with singular coefficients depending only on
one coordinate x_{0}. We express the Green functions by means of the Brownian
motion. Applying probabilistic methods we prove that when x=(0,{\bf x}) and
x^{\prime}=(0,{\bf x}^{\prime}) (here x_{0}=0) lie on the singular hyperplanes
then G(0,{\bf x};0,{\bf x}^{\prime}) is more regular than the Green function of
operators with regular coefficients.Comment: 16 page
Why the lowest Landau level approximation works in strongly type II superconductors
Higher than the lowest Landau level contributions to magnetization and
specific heat of superconductors are calculated using Ginzburg - Landau
equations approach. Corrections to the excitation spectrum around solution of
these equations (treated perturbatively) are found. Due to symmetries of the
problem leading to numerous cancellations the range of validity of the LLL
approximation in mean field is much wider then a naive range and extends all
the way down to . Moreover the contribution of higher
Landau levels is significantly smaller compared to LLL than expected naively.
We show that like the LLL part the lattice excitation spectrum at small
quasimomenta is softer than that of usual acoustic phonons. This enhanses the
effect of fluctuations. The mean field calculation extends to third order,
while the fluctuation contribution due to HLL is to one loop. This complements
the earlier calculation of the LLL part to two loop order.Comment: 20 pages, Latex file, three figure
The \Phi^4 quantum field in a scale invariant random metric
We discuss a D-dimensional Euclidean scalar field interacting with a scale
invariant quantized metric. We assume that the metric depends on d-dimensional
coordinates where d<D. We show that the interacting quantum fields have more
regular short distance behaviour than the free fields. A model of a Gaussian
metric is discussed in detail. In particular, in the \Phi^4 theory in four
dimensions we obtain explicit lower and upper bounds for each term of the
perturbation series. It turns out that there is no coupling constant
renormalization in the \Phi^4 model in four dimensions. We show that in a
particular range of the scale dimension there are models in D=4 without any
divergencies
Asymptotic symmetry and conservation laws in 2d Poincar\'e gauge theory of gravity
The structure of the asymptotic symmetry in the Poincar\'e gauge theory of
gravity in 2d is clarified by using the Hamiltonian formalism. The improved
form of the generator of the asymptotic symmetry is found for very general
asymptotic behaviour of phase space variables, and the related conserved
quantities are explicitly constructed.Comment: 22 pages, Plain Te
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