4,196 research outputs found
Correlation induced switching of local spatial charge distribution in two-level system
We present theoretical investigation of spatial charge distribution in the
two-level system with strong Coulomb correlations by means of Heisenberg
equations analysis for localized states total electron filling numbers taking
into account pair correlations of local electron density. It was found that
tunneling current through nanometer scale structure with strongly coupled
localized states causes Coulomb correlations induced spatial redistribution of
localized charges. Conditions for inverse occupation of two-level system in
particular range of applied bias caused by Coulomb correlations have been
revealed. We also discuss possibility of charge manipulation in the proposed
system.Comment: 6 pages, 4 figures Submitted to JETP Letter
Even-odd parity effects in conductance and shot noise of metal-atomic wire-metal(superconducting) junctions
In this paper, we study the conductance and shot noise in transport through a
multi-site system in a two terminal configuration. The dependence of the
transport on the number of atoms in the atomic wire is investigated using a
tight-binding Hamiltonian and the nonequilibrium Green's function method. In
addition to reproducing the even-odd behavior in the transmission probability
at the Fermi energy or the linear response conductance in the normal-atomic
wire-normal metallic(NAN) junctions, we find the following: (i) The shot noise
is larger in the even-numbered atomic wire than in the odd-numbered wire. (ii)
The Andreev conductance displays the same even-odd parity effects in the
normal-atomic wire-superconducting(NAS) junctions. In general, the conductance
is higher in the odd-numbered atomic wire than in the even-numbered wire. When
the number of sites () is odd and the atomic wire is mirror symmetric with
respect to the center of the atomic wire, the conductance does not depend on
the details of the hopping matrices in the atomic wire, but is solely
determined by the coupling strength to the two leads. When is even, the
conductance is sensitive to the values of the hopping matrices.Comment: 12 pages, 9 figure
Tunneling Conductance and Coulomb Blockade Peak Splitting of Two Quantum Dots Connected by a Quantum Point Contact
By using bosonization method and unitary transformation, we give a general
relation between the dimensionless tunneling conductance and the fractional
Coulomb blockade conductance peak splitting which is valid both for weak and
strong transmission between two quantum dots, and show that the tunneling
conductance has a linear temperature dependence in the low energy and low
temperature limit.Comment: 12 pages, Revtex, no figures, to appear in Phys. Rev.
Higher-Order Results for the Relation between Channel Conductance and the Coulomb Blockade for Two Tunnel-Coupled Quantum Dots
We extend earlier results on the relation between the dimensionless tunneling
channel conductance and the fractional Coulomb blockade peak splitting
for two electrostatically equivalent dots connected by an arbitrary number
of tunneling channels with bandwidths much larger than the
two-dot differential charging energy . By calculating through second
order in in the limit of weak coupling (), we illuminate
the difference in behavior of the large- and
small- regimes and make more plausible extrapolation to the
strong-coupling () limit. For the special case of
and strong coupling, we eliminate an apparent ultraviolet
divergence and obtain the next leading term of an expansion in . We show
that the results we calculate are independent of such band structure details as
the fraction of occupied fermionic single-particle states in the weak-coupling
theory and the nature of the cut-off in the bosonized strong-coupling theory.
The results agree with calculations for metallic junctions in the
limit and improve the previous good
agreement with recent two-channel experiments.Comment: 27 pages, 1 RevTeX file with 4 embedded Postscript figures. Uses eps
Ozone database in support of CMIP5 simulations: results and corresponding radiative forcing
A continuous tropospheric and stratospheric vertically resolved ozone time series, from 1850 to 2099, has been generated to be used as forcing in global climate models that do not include interactive chemistry. A multiple linear regression analysis of SAGE I+II satellite observations and polar ozonesonde measurements is used for the stratospheric zonal mean dataset during the well-observed period from 1979 to 2009. In addition to terms describing the mean annual cycle, the regression includes terms representing equivalent effective stratospheric chlorine (EESC) and the 11-yr solar cycle variability. The EESC regression fit coefficients, together with pre-1979 EESC values, are used to extrapolate the stratospheric ozone time series backward to 1850. While a similar procedure could be used to extrapolate into the future, coupled chemistry climate model (CCM) simulations indicate that future stratospheric ozone abundances are likely to be significantly affected by climate change, and capturing such effects through a regression model approach is not feasible. Therefore, the stratospheric ozone dataset is extended into the future (merged in 2009) with multimodel mean projections from 13 CCMs that performed a simulation until 2099 under the SRES (Special Report on Emission Scenarios) A1B greenhouse gas scenario and the A1 adjusted halogen scenario in the second round of the Chemistry-Climate Model Validation (CCMVal-2) Activity. The stratospheric zonal mean ozone time series is merged with a three-dimensional tropospheric data set extracted from simulations of the past by two CCMs (CAM3.5 and GISSPUCCINI)and of the future by one CCM (CAM3.5). The future tropospheric ozone time series continues the historical CAM3.5 simulation until 2099 following the four different Representative Concentration Pathways (RCPs). Generally good agreement is found between the historical segment of the ozone database and satellite observations, although it should be noted that total column ozone is overestimated in the southern polar latitudes during spring and tropospheric column ozone is slightly underestimated. Vertical profiles of tropospheric ozone are broadly consistent with ozonesondes and in-situ measurements, with some deviations in regions of biomass burning. The tropospheric ozone radiative forcing (RF) from the 1850s to the 2000s is 0.23Wm−2, lower than previous results. The lower value is mainly due to (i) a smaller increase in biomass burning emissions; (ii) a larger influence of stratospheric ozone depletion on upper tropospheric ozone at high southern latitudes; and possibly (iii) a larger influence of clouds (which act to reduce the net forcing) compared to previous radiative forcing calculations. Over the same period, decreases in stratospheric ozone, mainly at high latitudes, produce a RF of −0.08Wm−2, which is more negative than the central Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) value of −0.05Wm−2, but which is within the stated range of −0.15 to +0.05Wm−2. The more negative value is explained by the fact that the regression model simulates significant ozone depletion prior to 1979, in line with the increase in EESC and as confirmed by CCMs, while the AR4 assumed no change in stratospheric RF prior to 1979. A negative RF of similar magnitude persists into the future, although its location shifts from high latitudes to the tropics. This shift is due to increases in polar stratospheric ozone, but decreases in tropical lower stratospheric ozone, related to a strengthening of the Brewer-Dobson circulation, particularly through the latter half of the 21st century. Differences in trends in tropospheric ozone among the four RCPs are mainly driven by different methane concentrations, resulting in a range of tropospheric ozone RFs between 0.4 and 0.1Wm−2 by 2100. The ozone dataset described here has been released for the Coupled Model Intercomparison Project (CMIP5) model simulations in netCDF Climate and Forecast (CF) Metadata Convention at the PCMDI website (http://cmip-pcmdi.llnl.gov/)
Coulomb Blockade of Tunneling Through a Double Quantum Dot
We study the Coulomb blockade of tunneling through a double quantum dot. The
temperature dependence of the linear conductance is strongly affected by the
inter-dot tunneling. As the tunneling grows, a crossover from
temperature-independent peak conductance to a power-law suppression of
conductance at low temperatures is predicted. This suppression is a
manifestation of the Anderson orthogonality catastrophe associated with the
charge re-distribution between the dots, which accompanies the tunneling of an
electron into a dot. We find analytically the shapes of the Coulomb blockade
peaks in conductance as a function of gate voltage.Comment: 11 pages, revtex3.0 and multicols.sty, 4 figures uuencode
Nuclear Magnetic Resonance
Contains research objectives and reports on five research projects
Theory of strong inelastic co-tunneling
We develop a theory of the conductance of a quantum dot connected to two
leads by single-mode quantum point contacts. If the contacts are in the regime
of perfect transmission, the conductance shows no Coulomb blockade oscillations
as a function of the gate voltage. In the presence of small reflection in both
contacts, the conductance develops small Coulomb blockade oscillations. As the
temperature of the system is lowered, the amplitude of the oscillations grows,
and eventually sharp periodic peaks in conductance are formed. Away from the
centers of the peaks the conductance vanishes at low temperatures as , in
agreement with the theory of inelastic co-tunneling developed for the
weak-tunneling case. Conductance near the center of a peak can be studied using
an analogy with the multichannel Kondo problem. In the case of symmetric
barriers, the peak conductance at is of the order of . In
the asymmetric case, the peak conductance vanishes linearly in temperature.Comment: 22 pages, 4 figures, uses REVTEX 3.0, epsf.sty and multicol.st
Corrections to the universal behavior of the Coulomb-blockade peak splitting for quantum dots separated by a finite barrier
Building upon earlier work on the relation between the dimensionless interdot
channel conductance g and the fractional Coulomb-blockade peak splitting f for
two electrostatically equivalent dots, we calculate the leading correction that
results from an interdot tunneling barrier that is not a delta-function but,
rather, has a finite height V and a nonzero width xi and can be approximated as
parabolic near its peak. We develop a new treatment of the problem for g much
less than 1 that starts from the single-particle eigenstates for the full
coupled-dot system. The finiteness of the barrier leads to a small upward shift
of the f-versus-g curve at small values of g. The shift is a consequence of the
fact that the tunneling matrix elements vary exponentially with the energies of
the states connected. Therefore, when g is small, it can pay to tunnel to
intermediate states with single-particle energies above the barrier height V.
The correction to the zero-width behavior does not affect agreement with recent
experimental results but may be important in future experiments.Comment: Title changed from ``Non-universal...'' to ``Corrections to the
universal...'' No other changes. 10 pages, 1 RevTeX file with 2 postscript
figures included using eps
The role of the equation of state and the space-time dimension in spherical collapse
We study the spherically symmetric collapse of a fluid with non-vanishing
radial pressure in higher dimensional space-time. We obtain the general exact
solution in the closed form for the equation of state ()
which leads to the explicit construction of the root equation governing the
nature (black hole versus naked singularity) of the central singularity. A
remarkable feature of the root equation is its invariance for the three cases:
(),
() and () where is the
dimension of space-time. That is, for the ultimate end result of the collapse,
-dimensional dust, - AdS (anti de Sitter)-like and - dS-like
are absolutely equivalent.Comment: 4 Pages, RevTeX, no figures, minor changes, new references added,
Detailed version to follo
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