1,030,749 research outputs found
Superconductor-insulator transition in Coulomb disorder
Superconductor-insulator transition driven by the decreasing concentration of
electrons is studied in the case of the disorder potential created by
randomly positioned charged impurities. Electrons and Cooper pairs (formed by
an non-Coulomb attraction) nonlinearly screen the random potential of
impurities. Both electrons and Cooper pairs can be delocalized or localized in
the resulting self-consistent potential. The border separating the
superconductor and insulator phases in the plane of the concentration of
electrons and the length of the Cooper pair is found. For a strong disorder the
central segment of this border follows the BEC-BCS crossover line defined for a
clean sample.Comment: 4.5 pages, introduction rewritten, a dozen of references added, 2D
case adde
Hopping conductivity of a suspension of nanowires in an insulator
We study the hopping conduction in a composite made of straight metallic
nanowires randomly and isotropically suspended in an insulator. Uncontrolled
donors and acceptors in the insulator lead to random charging of wires and
hence finite bare density of states at the Fermi level. Then the Coulomb
interactions between electrons of distant wires result in the soft Coulomb gap.
At low temperatures the conductivity is due to variable range hopping of
electrons between wires and obeys the Efros-Shklovskii (ES) law . We show that , where
is the concentration of wires and is the wire length. Due to enhanced
screening of Coulomb potentials, at large enough , the ES law is replaced
by the Mott law.Comment: 5 pages, 5 figure
On Low-Energy Effective Action of Noncommutative Hypermultiplet Model
We consider the noncommutative hypermultiplet model within harmonic
superspace approach. The 1-loop four-point contributions to the effective
action of selfinteracting q-hypermultiplet are computed. This model has two
coupling constants instead of a single one in commutative case. It is shown
that both these coupling constants are generated by 1-loop quantum corrections
in the model of q-hypermultiplet interacting with vector multiplet. The
holomorphic effective action of q-hypermultiplet in external gauge superfield
is calculated. For the fundamental representation there is no UV/IR-mixing and
the holomorphic potential is a star-product generalization of a standard
commutative one. For the adjoint representation of U(N) gauge group the leading
contributions to the holomorphic effective action are given by the terms
respecting for the UV/IR-mixing which are related to U(1) phase of U(N) group.Comment: 13 pages, 4 figures. v2: minor changes, refs adde
A simple model of Coulomb disorder and screening in graphene
We suggest a simple model of disorder in graphene assuming that there are
randomly distributed positive and negative centers with equal concentration
in the bulk of silicon oxide substrate. We show that at zero gate voltage
such disorder creates two-dimensional concentration of
electrons and holes in graphene. Electrons and holes reside in alternating in
space puddles of the size . A typical puddle has only one or
two carriers in agreement with recent scanning single electron transistor
experiment.Comment: 2.5 pages, twice longer than previous versio
Spin-fluctuation theory beyond Gaussian approximation
A characteristic feature of the Gaussian approximation in the
functional-integral approach to the spin-fluctuation theory is the jump phase
transition to the paramagnetic state. We eliminate the jump and obtain a
continuous second-order phase transition by taking into account high-order
terms in the expansion of the free energy in powers of the fluctuating exchange
field. The third-order term of the free energy renormalizes the mean field, and
fourth-order term, responsible for the interaction of the fluctuations,
renormalizes the spin susceptibility. The extended theory is applied to the
calculation of magnetic properties of Fe-Ni Invar.Comment: 20 pages, 4 figure
Two-loop low-energy effective action in Abelian supersymmetric Chern-Simons matter models
We compute two-loop low-energy effective actions in Abelian Chern-Simons
matter models with N=2 and N=3 supersymmetry up to four-derivative order.
Calculations are performed with a slowly-varying gauge superfield background.
Though the gauge superfield propagator depends on the gauge fixing parameter,
it is shown that the obtained results are independent of this parameter. In the
massless case the considered models are superconformal. We demonstrate that the
superconformal symmetry strongly restricts the form of two-loop quantum
corrections to the effective actions such that the obtained terms have simpler
structure than the analogous ones in the effective action of three-dimensional
supersymmetric electrodynamics (SQED) with vanishing topological mass.Comment: 1+30 pages; v2: references added, misprints corrected; v3: minor
changes, published versio
Conductance noise in interacting Anderson insulators driven far from equilibrium
The combination of strong disorder and many-body interactions in Anderson
insulators lead to a variety of intriguing non-equilibrium transport phenomena.
These include slow relaxation and a variety of memory effects characteristic of
glasses. Here we show that when such systems are driven with sufficiently high
current, and in liquid helium bath, a peculiar type of conductance noise can be
observed. This noise appears in the conductance versus time traces as
downward-going spikes. The characteristic features of the spikes (such as
typical width) and the threshold current at which they appear are controlled by
the sample parameters. We show that this phenomenon is peculiar to hopping
transport and does not exist in the diffusive regime. Observation of
conductance spikes hinges also on the sample being in direct contact with the
normal phase of liquid helium; when this is not the case, the noise exhibits
the usual 1/f characteristics independent of the current drive. A model based
on the percolative nature of hopping conductance explains why the onset of the
effect is controlled by current density. It also predicts the dependence on
disorder as confirmed by our experiments. To account for the role of the bath,
the hopping transport model is augmented by a heuristic assumption involving
nucleation of cavities in the liquid helium in which the sample is immersed.
The suggested scenario is analogous to the way high-energy particles are
detected in a Glaser's bubble chamber.Comment: 15 pages 22 figure
Non-Linear Compton Scattering of Ultrashort and Ultraintense Laser Pulses
The scattering of temporally shaped intense laser pulses off electrons is
discussed by means of manifestly covariant quantum electrodynamics. We employ a
framework based on Volkov states with a time dependent laser envelope in
light-cone coordinates within the Furry picture. An expression for the cross
section is constructed, which is independent of the considered pulse shape and
pulse length. A broad distribution of scatted photons with a rich pattern of
subpeaks like that obtained in Thomson scattering is found. These broad peaks
may overlap at sufficiently high laser intensity, rendering inappropriate the
notion of individual harmonics. The limit of monochromatic plane waves as well
as the classical limit of Thomson scattering are discussed. As a main result, a
scaling law is presented connecting the Thomson limit with the general result
for arbitrary kinematics. In the overlapping regions of the spectral density,
the classical and quantum calculations give different results, even in the
Thomson limit. Thus, a phase space region is identified where the differential
photon distribution is strongly modified by quantum effects.Comment: 31 pages, 10 figure
A Novel Approach of Virotherapy Based Hsf-1 Shrna in Cancer Eradication
Cancer is the second leading cause of death worldwide with continues rise mortality rate. Current cancer treatment modalities are still ineffective and associated with many side effects leading to robust research to find new specific target therapy. Heat shock factor (HSF)-1 is heat shock response mediator protein and act as transcription factor for HSP encoding gene. Many cancers have up-regulated HSP as a result of increase HSF-1 expression. Interestingly, inhibition of HSF-1 has no effect to normal cell, indicating HSF-1 as promises target therapy. RNAi is potential mechanism to block and down regulate HSF-1 which will affect many cellular processes in cancer cell. Combining RNAi base treatment with oncolityc viruses will boost the therapeutic effect of this novel treatment. Despite its potency, this modality still need further research in order to evaluate its efficacy and optimal doses to gain optimal result
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