23,476 research outputs found
Generalized -conformal change and special Finsler spaces
In this paper, we investigate the change of Finslr metrics which we refer to as a
generalized -conformal change. Under this change, we study some special
Finsler spaces, namely, quasi C-reducible, semi C-reducible, C-reducible,
-like, -like and -like Finsler spaces. We also obtain the
transformation of the T-tensor under this change and study some interesting
special cases. We then impose a certain condition on the generalized
-conformal change, which we call the b-condition, and investigate the
geometric consequences of such condition. Finally, we give the conditions under
which a generalized -conformal change is projective and generalize some
known results in the literature.Comment: References added, some modifications are performed, LateX file, 24
page
Elasticity-Driven Nanoscale Electronic Structure in Superconductors
The effects of long-range anisotropic elastic deformations on electronic
structure in superconductors are analyzed within the framework of the
Bogoliubov-de Gennes equations. Cases of twin boundaries and isolated defects
are considered as illustrations. We find that the superconducting order
parameter is depressed in the regions where pronounced lattice deformation
occurs. The calculated local density of states suggests that the electronic
structure is strongly modulated in response to lattice deformations, and
propagates to longer distances. In particular, this allows the trapping of
low-lying quasiparticle states around defects. Some of our predictions can be
directly tested by STM experiments.Comment: 5 pages, 5 figures, reference added, accepted to Physical Review
Letter
Impurity spin textures across conventional and deconfined quantum critical points of two-dimensional antiferromagnets
We describe the spin distribution in the vicinity of a non-magnetic impurity
in a two-dimensional antiferromagnet undergoing a transition from a
magnetically ordered Neel state to a paramagnet with a spin gap. The quantum
critical ground state in a finite system has total spin S=1/2 (if the system
without the impurity had an even number of S=1/2 spins), and recent numerical
studies in a double layer antiferromagnet (K. H.Hoglund et al.,
cond-mat/0611418) have shown that the spin has a universal spatial form
delocalized across the entire sample. We present the field theory describing
the uniform and staggered magnetizations in this spin texture for two classes
of antiferromagnets: (i) the transition from a Neel state to a paramagnet with
local spin singlets, in models with an even number of S=1/2 spins per unit
cell, which are described by a O(3) Landau-Ginzburg-Wilson field theory; and
(ii) the transition from a Neel state to a valence bond solid, in
antiferromagnets with a single S=1/2 spin per unit cell, which are described by
a deconfined field theory of spinons.Comment: 30 pages, 9 figure
Single Impurity Effects in Multiband Superconductors with Different Sign Order Parameters
A single impurity problem is investigated for multiband s-wave
superconductors with different sign order parameters (+-s-wave superconductors)
suggested in Fe-pnictide superconductors. Not only intraband but also interband
scattering is considered at the impurity. The latter gives rise to
impurity-induced local boundstates close to the impurity. We present an exact
form of the energy of the local boundstates as a function of strength of the
two types of impurity scattering. The essential role of the impurity is
unchanged in finite number of impurities. The main conclusions for a single
impurity problem help us understand effects of dense impurities in the +-s-wave
superconductors. Local density of states around the single impurity is also
investigated. We suggest impurity site nuclear magnetic resonance as a suitable
experiment to probe the local boundstates that is peculiar to the +-s-wave
state. We find that the +-s-wave model is mapped to a chiral dx2-y2+-idxy-wave,
reflecting the unconventional nature of the sign reversing order parameter. For
a quantum magnetic impurity, interband scattering destabilizes the Kondo
singlet.Comment: 23 pages, 7 figures, to be published in J. Phys. Soc. Jpn. (2009) No.
On the Bloch Theorem Concerning Spontaneous Electric Current
We study the Bloch theorem which states absence of the spontaneous current in
interacting electron systems. This theorem is shown to be still applicable to
the system with the magnetic field induced by the electric current. Application
to the spontaneous surface current is also examined in detail. Our result
excludes the possibility of the recently proposed -wave superconductivity
having the surface flow and finite total current.Comment: 12 pages, LaTeX, 3 Postscript figure
Tunneling spectra for ()-wave superconductors versus tunneling spectra for ()-wave superconductors
The tunneling conductance spectra of a normal metal / insulator / singlet
superconductor is calculated from the reflection amplitudes using the
Blonder-Tinkham-Klapwijk (BTK) formulation. The pairing symmetry of the
superconductor is assumed to be , or . It
is found that in the ()-wave case there is a well defined
conductance peak in the conductance spectra, in the amplitude of the secondary
s-wave component. In the ()-wave case the tunneling
conductance has residual values within the gap, due to the formation of bound
states. The bound state energies depend on the angle of the incident
quasiparticles, and also on the boundary orientation. On the basis of this
observation an electron focusing experiment is proposed to probe the
()-wave state.Comment: 17 pages with 9 figure
New Kinetic Equation for Pair-annihilating Particles: Generalization of the Boltzmann Equation
A convenient form of kinetic equation is derived for pair annihilation of
heavy stable particles relevant to the dark matter problem in cosmology. The
kinetic equation thus derived extends the on-shell Boltzmann equation in a most
straightforward way, including the off-shell effect. A detailed balance
equation for the equilibrium abundance is further analyzed. Perturbative
analysis of this equation supports a previous result for the equilibrium
abundance using the thermal field theory, and gives the temperature power
dependence of equilibrium value at low temperatures. Estimate of the relic
abundance is possible using this new equilibrium abundance in the sudden
freeze-out approximation.Comment: 19 pages, LATEX file with 2 PS figure
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