13,400 research outputs found
Shot Noise in Ballistic Graphene
We have investigated shot noise in graphene field effect devices in the
temperature range of 4.2--30 K at low frequency ( = 600--850 MHz). We find
that for our graphene samples with large width over length ratio , the
Fano factor reaches a maximum 1/3 at the
Dirac point and that it decreases strongly with increasing charge density. For
smaller , the Fano factor at Dirac point is significantly lower. Our
results are in good agreement with the theory describing that transport at the
Dirac point in clean graphene arises from evanescent electronic states.Comment: Phys. Rev. Lett. 100, 196802 (2008
Adiabatic quantum pumping at the Josephson frequency
We analyze theoretically adiabatic quantum pumping through a normal conductor
that couples the normal regions of two superconductor/normal
metal/superconductor Josephson junctions. By using the phases of the
superconducting order parameter in the superconducting contacts as pumping
parameters, we demonstrate that a non zero pumped charge can flow through the
device. The device exploits the evolution of the superconducting phases due to
the ac Josephson effect, and can therefore be operated at very high frequency,
resulting in a pumped current as large as a few nanoAmperes. The experimental
relevance of our calculations is discussed.Comment: 4 pages, 3 figure
Initial singularity free quantum cosmology in two-dimensional Brans-Dicke theory
We consider two-dimensional Brans-Dicke theory to study the initial
singularity problem. It turns out that the initial curvature singularity can be
finite for a certain Brans-Dicke constant by considering the quantum
back reaction of the geometry. For , the universe starts with the
finite curvature scalar and evolves into the flat spacetime. Furthermore the
divergent gravitational coupling at the initial time can be finite effectively
with the help of quantum correction. The other type of universe is studied for
the case of .Comment: 12 pages, 4 figures, revtex, Some references are added. To be
published in Phys. Rev.
Unforeseen high temperature and humidity stability of FeCl intercalated few layer graphene
We present the first systematic study of the stability of the structure and
electrical properties of FeCl intercalated few-layer graphene to high
levels of humidity and high temperature. Complementary experimental techniques
such as electrical transport, high resolution transmission electron microscopy
and Raman spectroscopy conclusively demonstrate the unforeseen stability of
this transparent conductor to a relative humidity up to at room
temperature for 25 days, to a temperature up to 150\,^\circC in atmosphere
and up to a temperature as high as 620\,^\circC in vacuum, that is more than
twice higher than the temperature at which the intercalation is conducted. The
stability of FeCl intercalated few-layer graphene together with its unique
values of low square resistance and high optical transparency, makes this
material an attractive transparent conductor in future flexible electronic
applications.Comment: Scientific Reports, volume 5, article no. 760
Decay Modes of Intersecting Fluxbranes
Just as the single fluxbrane is quantum mechanically unstable to the
nucleation of a locally charged spherical brane, so intersecting fluxbranes are
unstable to various decay modes. Each individual element of the intersection
can decay via the nucleation of a spherical brane, but uncharged spheres can
also be nucleated in the region of intersection. For special values of the
fluxes, however, intersecting fluxbranes are supersymmetric, and so are
expected to be stable. We explicitly consider the instanton describing the
decay modes of the two--element intersection (an F5-brane in the string theory
context), and show that in dimensions greater than four the action for the
decay mode of the supersymmetric intersection diverges. This observation allows
us to show that stable intersecting fluxbranes should also exist in type 0A
string theory.Comment: 19 pages, 6 figures. References adde
Soluble models in 2d dilaton gravity
A one-parameter class of simple models of two-dimensional dilaton gravity,
which can be exactly solved including back-reaction effects, is investigated at
both classical and quantum levels. This family contains the RST model as a
special case, and it continuously interpolates between models having a flat
(Rindler) geometry and a constant curvature metric with a non-trivial dilaton
field. The processes of formation of black hole singularities from collapsing
matter and Hawking evaporation are considered in detail. Various physical
aspects of these geometries are discussed, including the cosmological
interpretation.Comment: 15 pages, harvmac, 3 figure
Study of the general mechanism of stress corrosion of aluminum alloys and development of techniques for its detection Quarterly report, 1 Dec. 1967 - 29 Feb. 1968
Stress corrosion of aluminum alloys and techniques for its detectio
A New Cosmological Scenario in String Theory
We consider new cosmological solutions with a collapsing, an intermediate and
an expanding phase. The boundary between the expanding (collapsing) phase and
the intermediate phase is seen by comoving observers as a cosmological past
(future) horizon. The solutions are naturally embedded in string and M-theory.
In the particular case of a two-dimensional cosmology, space-time is flat with
an identification under boost and translation transformations. We consider the
corresponding string theory orbifold and calculate the modular invariant
one-loop partition function. In this case there is a strong parallel with the
BTZ black hole. The higher dimensional cosmologies have a time-like curvature
singularity in the intermediate region. In some cases the string coupling can
be made small throughout all of space-time but string corrections become
important at the singularity. This happens where string winding modes become
light which could resolve the singularity. The new proposed space-time casual
structure could have implications for cosmology, independently of string
theory.Comment: 28 pages, 3 figures; v2: Added new subsection relating
two-dimensional model to BTZ black hole, typos corrected and references
added; v3: minor corrections, PRD versio
Study of the general mechanism of stress corrosion of aluminum alloys and development of techniques for its detection Annual summary report, 2 Jun. 1967 - 1 Jun. 1968
Stress corrosion cracking of high strength aluminum alloys investigated by electrochemical, mechanical, and electron microscopic technique
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