1,616 research outputs found
Knots in a Spinor Bose-Einstein Condensate
We show that knots of spin textures can be created in the polar phase of a
spin-1 Bose-Einstein condensate, and discuss experimental schemes for their
generation and probe, together with their lifetime.Comment: 4 pages, 3 figure
Birman-Schwinger and the number of Andreev states in BCS superconductors
The number of bound states due to inhomogeneities in a BCS superconductor is
usually established either by variational means or via exact solutions of
particularly simple, symmetric perturbations. Here we propose estimating the
number of sub-gap states using the Birman-Schwinger principle. We show how to
obtain upper bounds on the number of sub-gap states for small normal regions
and derive a suitable Cwikel-Lieb-Rozenblum inequality. We also estimate the
number of such states for large normal regions using high dimensional
generalizations of the Szego theorem. The method works equally well for local
inhomogeneities of the order parameter and for external potentials.Comment: Final version to appear in Phys Rev
Conductance enhancement due to the resonant tunneling into the subgap vortex core states in normal metal/superconductor ballistic junctions
We investigate the low-energy quantum transport in the ballistic normal
metal-insulator -superconductor junction in the presence of magnetic field
creating Abrikosov vortices in the superconductor. Within the Bogolubov- de
Gennes theory we show that the presence of the subgap quasiparticle states
localized within the vortex cores near the junction interface leads to the
strong resonant enhancement of the Andreev reflection probability, and the
normal-to supercurrent conversion. The corresponding increase of the charge
conductance of the junction is determined by the distance from the vortex chain
to the junction interface, which can be controlled by the applied magnetic
field. The effect that we study provides a tool for probing the vortex core
states by the measurements of charge transport across the applied magnetic
field.Comment: 8 pages, 3 figure
Nodal Structure of Superconductors with Time-Reversal Invariance and Z2 Topological Number
A topological argument is presented for nodal structures of superconducting
states with time-reversal invariance. A generic Hamiltonian which describes a
quasiparticle in superconducting states with time-reversal invariance is
derived, and it is shown that only line nodes are topologically stable in
single-band descriptions of superconductivity. Using the time-reversal
symmetry, we introduce a real structure and define topological numbers of line
nodes. Stability of line nodes is ensured by conservation of the topological
numbers. Line nodes in high-Tc materials, the polar state in p-wave paring and
mixed singlet-triplet superconducting states are examined in detail.Comment: 11 pages, 8 figure
Coexistence of different vacua in the effective quantum field theory and Multiple Point Principle
According to the Multiple Point Principle our Universe is on the coexistence
curve of two or more phases of the quantum vacuum. The coexistence of different
quantum vacua can be regulated by the exchange of the global fermionic charges
between the vacua, such as baryonic, leptonic or family charge. If the
coexistence is regulated by the baryonic charge, all the coexisting vacua
exhibit the baryonic asymmetry. Due to the exchange of the baryonic charge
between the vacuum and matter which occurs above the electroweak transition,
the baryonic asymmetry of the vacuum induces the baryonic asymmetry of matter
in our Standard-Model phase of the quantum vacuum. The present baryonic
asymmetry of the Universe indicates that the characteristic energy scale which
regulates the equilibrium coexistence of different phases of quantum vacua is
about 10^6 GeV.Comment: 12 pages, 1 figure, modified version submitted to JETP letter
Fermions on half-quantum vortex
The spectrum of the fermion zero modes in the vicinity of the vortex with
fractional winding number is discussed. This is inspired by the observation of
the 1/2 vortex in high-temperature superconductors (Kirtley, et al, Phys. Rev.
Lett. 76 (1996) 1336). The fractional value of the winding number leads to the
fractional value of the invariant, which describes the topology of the energy
spectrum of fermions. This results in the phenomenon of the "half-crossing":
the spectrum approaches zero but does not cross it, being captured at the zero
energy level. The similarity with the phenomenon of the fermion condensation is
discussed.Comment: In revised version the discussion is extended and 4 references are
added. The paper is accepted for publication in JETP Letters. 10 pages, LaTeX
file, 3 figures are available at
ftp://boojum.hut.fi/pub/publications/lowtemp/LTL-96004.p
Spin-Hall effect in triplet chiral superconductors and graphene
We study spin-Hall effects in time-reversal symmetry (TRS) broken systems
such as triplet chiral superconductors and TRS preserved ones such as graphene.
For chiral triplet superconductors, we show that the edge states carry a
quantized spin-Hall current in response to an applied Zeeman magnetic field
along the vector \cite{leggett1}, whereas the edge spin-current for
is screened by the condensate. We also derive the bulk
spin-Hall current for chiral triplet superconductors for arbitrary relative
orientation of and and discuss its relation with the edge
spin-current. For TRS invariant system graphene, we show that the bulk
effective action, unlike its TRS broken counterparts, does not support a SU(2)
Hopf term but allows a crossed Hopf term in the presence of an external
electromagnetic field, which yields a quantized bulk spin-Hall current in
response to an electric field. We also present an analytical solution of the
edge problem for armchair edges of graphene and contrast the properties of
these edge states with their time reversal symmetry broken counterparts in
chiral superconductors. We propose possible experiments to test our results.Comment: v2; minor changes, additional ref
Magnetic resonance within vortex cores in the B phase of superfluid He
We investigate a magnetic susceptibility of vortices in the B phase of
multicomponent triplet superfluid He focusing on a contribution of bound
fermionic states localized within vortex cores. Several order parameter
configurations relevant to different types of quantized vortices in He B
are considered. It is shown quite generally that an ac magnetic susceptibility
has a sharp peak at the frequency corresponding to the energy of interlevel
spacing in the spectrum of bound fermions. We suggest that measuring of a
magnetic resonance within vortex cores can provide a direct probe of a discrete
spectrum of bound vortex core excitations
Gravity of Monopole and String and Gravitational Constant in 3He-A
We discuss the effective metric produced in superfluid 3He-A by such
topological objects as radial disgyration and monopole. In relativistic
theories these metrics are similar to that of the local string and global
monopole correspondingly. But in 3He-A they have the negative angle deficit,
which corresponds to the negative mass of the topological objects. The
effective gravitational constant G in superfluid 3He-A, derived from the
comparison with relativistic theories, is inversely proportional to the square
of the gap amplitude Delta, which plays the part of the Planck energy cut-off.
G depends on temperature and increases with T, which corresponds to the vacuum
screening of the Newton's constant.Comment: Latex file, 10 pages, no figure
The Nambu sum rule and the relation between the masses of composite Higgs bosons
We review the known results on the bosonic spectrum in various NJL models
both in the condensed matter physics and in relativistic quantum field theory
including He-B, He-A, the thin films of superfluid He-3, and QCD
(Hadronic phase and the Color Flavor Locking phase). Next, we calculate bosonic
spectrum in the relativistic model of top quark condensation suggested in
\cite{Miransky}. In all considered cases the sum rule appears that relates the
masses (energy gaps) of the bosonic excitations in each channel
with the mass (energy gap) of the condensed fermion as . Previously this relation was established by Nambu in \cite{Nambu}
for He-B and for the s - wave superconductor. We generalize this relation
to the wider class of models and call it the Nambu sum rule. We discuss the
possibility to apply this sum rule to various models of top quark condensation.
In some cases this rule allows to calculate the masses of extra Higgs bosons
that are the Nambu partners of the 125 GeV Higgs.Comment: Latex, 15 page
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