176 research outputs found
Weak antilocalization in a 2D electron gas with the chiral splitting of the spectrum
Motivated by the recent observation of the metal-insulator transition in
Si-MOSFETs we consider the quantum interference correction to the conductivity
in the presence of the Rashba spin splitting. For a small splitting, a
crossover from the localizing to antilocalizing regime is obtained. The
symplectic correction is revealed in the limit of a large separation between
the chiral branches. The relevance of the chiral splitting for the 2D electron
gas in Si-MOSFETs is discussed.Comment: 7 pages, REVTeX. Mistake corrected; in the limit of a large chiral
splitting the correction to the conductivity does not vanish but approaches
the symplectic valu
Conformal self-dual fields
Conformal self-dual fields in flat space-time of even dimension greater than
or equal to four are studied. Ordinary-derivative formulation of such fields is
developed. Gauge invariant Lagrangian with conventional kinetic terms and
corresponding gauge transformations are obtained. Gauge symmetries are realized
by involving the Stueckelberg fields. Realization of global conformal
symmetries is obtained. Light-cone gauge Lagrangian is found. Also, we
demonstrate use of the light-cone gauge for counting of on-shell degrees of
freedom of the conformal self-dual fields.Comment: 28 pages, LaTeX-2e, v3: Discussion of realization of conformal
algebra symmetries on field strengths added to Sections 3,5. Appendices B,C,D
and one reference added. Typos correcte
Coulomb blockade in quantum dots under AC pumping
We study conductance through a quantum dot under Coulomb blockade conditions
in the presence of an external periodic perturbation. The stationary state is
determined by the balance between the heating of the dot electrons by the
perturbation and cooling. We analyze two cooling mechanisms: electron exchange
with the cold contacts and emission of phonons. Together with the usual linear
Ohmic heating of the dot electrons we consider possible effects of dynamic
localization. The combination of the abovementioned factors may result in a
drastic change of the shape of the Coulomb blockade peak with respect to the
usual equilibrium one.Comment: 12 pages, 8 figure
BRST approach to Lagrangian formulation of bosonic totally antisymmeric tensor fields in curved space
We apply the BRST approach, previously developed for higher spin field
theories, to gauge invariant Lagrangian construction for antisymmetric massive
and massless bosonic fields in arbitrary d-dimensional curved space. The
obtained theories are reducible gauge models both in massless and massive cases
and the order of reducibility grows with the value of the rank of the
antisymmetric field. In both the cases the Lagrangians contain the sets of
auxiliary fields and possess more rich gauge symmetry in comparison with
standard Lagrangian formulation for the antisymmetric fields. This serves
additional demonstration of universality of the BRST approach for Lagrangian
constructions in various field models.Comment: 12 page
Proximity-induced superconductivity in graphene
We propose a way of making graphene superconductive by putting on it small
superconductive islands which cover a tiny fraction of graphene area. We show
that the critical temperature, T_c, can reach several Kelvins at the
experimentally accessible range of parameters. At low temperatures, T<<T_c, and
zero magnetic field, the density of states is characterized by a small gap
E_g<T_c resulting from the collective proximity effect. Transverse magnetic
field H_g(T) E_g is expected to destroy the spectral gap driving graphene layer
to a kind of a superconductive glass state. Melting of the glass state into a
metal occurs at a higher field H_{g2}(T).Comment: 4 pages, 3 figure
On electromagnetic interactions for massive mixed symmetry field
In this paper we investigate electromagnetic interactions for simplest
massive mixed symmetry field. Using frame-like gauge invariant formulation we
extend Fradkin-Vasiliev procedure, initially proposed for investigation of
gravitational interactions for massless particles in AdS space, to the case of
electromagnetic interactions for massive particles leaving in (A)dS space with
arbitrary value of cosmological constant including flat Minkowski space. At
first, as an illustration of general procedure, we re-derive our previous
results on massive spin 2 electromagnetic interactions and then we apply this
procedure to massive mixed symmetry field. These two cases are just the
simplest representatives of two general class of fields, namely completely
symmetric and mixed symmetry ones, and it is clear that the results obtained
admit straightforward generalization to higher spins as well.Comment: 17 pages. Some clarifications added. Version to appear in JHE
Helicobacter pylori roles in haematology disease pathogenesis
Helicobacter pylori is considered to be one of the significant reasons of formation of gastroduodenal pathology. Data on the role of H. pylori in the development of extragastric diseases are confirmed by a positive effect of eradication on peripheral blood changes. In spite of this fact both aspects are still not revealed. However, undoubtedly that H. pylori persistence on gastric epithelium creates conditions for chronic local and systematic inflammation. The aim of the sur- vey was the analysis of literary data about bacterial factors in the development of iron-, vitamin B12-deficiency anaemia and thrombocytopenic purpura included by the international consensus into the circle of evedences for diagnosis and treatment of H. pylori. Material and methods. There was accomplished search of literature sources with the help of data bases PubMed, CyberLeninka, eLibrary, Google Scholar. The results of our analysis specify mechanisms of cer- tain blood diseases pathogenesis in association with H. pylori. Multiple roles of virulent strains of pathogen in anaemia and thrombocytopenic purpura include: development of erosive and ulcerative lesions of mucosa, hypoacidity, chron- ic inflammation and autoimmune response. Data about these changes in haematological syndromes and independent eradication effects on blood parameters normalisation, are controversial. Н. pylori host iron competition theory has not been found convincing confirmation. Conclusions. It is necessary to study more deeply the connection of H. pylori and haematological diseases. The dietary research and application to maintain the mucous integrity and bacterial adhesion prevention are perspective
Critical disorder effects in Josephson-coupled quasi-one-dimensional superconductors
Effects of non-magnetic randomness on the critical temperature T_c and
diamagnetism are studied in a class of quasi-one dimensional superconductors.
The energy of Josephson-coupling between wires is considered to be random,
which is typical for dirty organic superconductors. We show that this
randomness destroys phase coherence between the wires and T_c vanishes
discontinuously when the randomness reaches a critical value. The parallel and
transverse components of the penetration depth are found to diverge at
different critical temperatures T_c^{(1)} and T_c, which correspond to
pair-breaking and phase-coherence breaking. The interplay between disorder and
quantum phase fluctuations results in quantum critical behavior at T=0,
manifesting itself as a superconducting-normal metal phase transition of
first-order at a critical disorder strength.Comment: 4 pages, 2 figure
Keldysh action for disordered superconductors
Keldysh representation of the functional integral for the interacting
electron system with disorder is used to derive microscopically an effective
action for dirty superconductors. In the most general case this action is a
functional of the 8 x 8 matrix Q(t,t') which depends on two time variables, and
on the fluctuating order parameter field and electric potential. We show that
this approach reproduces, without the use of the replica trick, the well-known
result for the Coulomb-induced renormalization of the electron-electron
coupling constant in the Cooper channel. Turning to the new results, we
calculate the effects of the Coulomb interaction upon: i) the subgap Andreev
conductance between superconductor and 2D dirty normal metal, and ii) the
Josephson proximity coupling between superconductive islands via such a metal.
These quantities are shown to be strongly suppressed by the Coulomb interaction
at sufficiently low temperatures due to both zero-bias anomaly in the density
of states and disorder-enhanced repulsion in the Cooper channel.Comment: RevTeX; 39 pages + 10 EPS figure
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