111 research outputs found
Fermi liquid theory for the Anderson model out of equilibrium
We study low-energy properties of the Anderson impurity under a finite bias
voltage using the perturbation theory in of Yamada and Yosida in the
nonequilibrium Keldysh diagrammatic formalism, and obtain the Ward identities
for the derivative of the self-energy with respect to . The self-energy is
calculated exactly up to terms of order , and , and the
coefficients are defined with respect to the equilibrium ground state. From
these results, the nonlinear response of the current through the impurity has
been deduced up to order .Comment: 8 pages, 1 figur
Dynamical 1/N approach to time-dependent currents through quantum dots
A systematic truncation of the many-body Hilbert space is implemented to
study how electrons in a quantum dot attached to conducting leads respond to
time-dependent biases. The method, which we call the dynamical 1/N approach, is
first tested in the most unfavorable case, the case of spinless fermions (N=1).
We recover the expected behavior, including transient ringing of the current in
response to an abrupt change of bias. We then apply the approach to the
physical case of spinning electrons, N=2, in the Kondo regime for the case of
infinite intradot Coulomb repulsion. In agreement with previous calculations
based on the non-crossing approximation (NCA), we find current oscillations
associated with transitions between Kondo resonances situated at the Fermi
levels of each lead. We show that this behavior persists for a more realistic
model of semiconducting quantum dots in which the Coulomb repulsion is finite.Comment: 18 pages, 7 eps figures, discussion extended for spinless electrons
and typo
Hadean geodynamics inferred from time-varying 142Nd/144Nd in the early Earth rock record
Tracking the secular evolution of 142Nd/144Nd anomalies is important towards
understanding the crust-mantle dynamics in the early Earth. Excessive scatter in
the published data, however, precludes identifying the fine structure of
142Nd/144Nd evolution as the expected variability is on the order of few parts per
million. We report ultra-high precision 142Nd/144Nd data for Eoarchean and
Palaeoarchean rocks from the Isua Supracrustal Belt (SW Greenland) that show
a well-resolved 142Nd/144Nd temporal variability suggesting progressive convective
homogenisation of the Hadean Isua depleted mantle. This temporally
decreasing 142Nd/144Nd signal provides a direct measure of early mantle dynamics,
defining a stirring timescale of <250 Myr consistent with vigorous convective
stirring in the early mantle. The 142Nd/144Nd evolution suggests protracted crustal
residence times of ~1000-2000 Myr, inconsistent with modern-style plate tectonics
in the Archean. In contrast, a stagnant-lid regime punctuated by episodes of mantle overturns accounts for the long life-time
estimated here for the Hadean proto-crust
Non-linear response of a Kondo system: Perturbation approach to the time dependent Anderson impurity model
Nonlinear tunneling current through a quantum dot
(an Anderson impurity system) subject to both constant and alternating
electric fields is studied in the Kondo regime. A systematic diagram technique
is developed for perturbation study of the current in physical systems out of
equilibrium governed by time - dependent Hamiltonians of the Anderson and the
Kondo models. The ensuing calculations prove to be too complicated for the
Anderson model, and hence, a mapping on an effective Kondo problem is called
for. This is achieved by constructing a time - dependent version of the
Schrieffer - Wolff transformation. Perturbation expansion of the current is
then carried out up to third order in the Kondo coupling J yielding a set of
remarkably simple analytical expressions for the current. The zero - bias
anomaly of the direct current differential conductance is shown to be
suppressed by the alternating field while side peaks develop at finite source -
drain voltage. Both the direct component and the first harmonics of the time -
dependent response are equally enhanced due to the Kondo effect, while
amplitudes of higher harmonics are shown to be relatively small. A zero
alternating bias anomaly is found in the alternating current differential
conductance, that is, it peaks around zero alternating bias. This peak is
suppressed by the constant bias. No side peaks show up in the differential
alternating - conductance but their counterpart is found in the derivative of
the alternating current with respect to the direct bias. The results pertaining
to nonlinear response are shown to be valid also below the Kondo temperature.Comment: 55 latex pages 11 ps figure
Nonequilibrium Transport through a Kondo Dot in a Magnetic Field: Perturbation Theory
Using nonequilibrium perturbation theory, we investigate the nonlinear
transport through a quantum dot in the Kondo regime in the presence of a
magnetic field. We calculate the leading logarithmic corrections to the local
magnetization and the differential conductance, which are characteristic of the
Kondo effect out of equilibrium. By solving a quantum Boltzmann equation, we
determine the nonequilibrium magnetization on the dot and show that the
application of both a finite bias voltage and a magnetic field induces a novel
structure of logarithmic corrections not present in equilibrium. These
corrections lead to more pronounced features in the conductance, and their form
calls for a modification of the perturbative renormalization group.Comment: 16 pages, 7 figure
Low temperature transport in AC-driven Quantum Dots in the Kondo regime
We present a fully nonequilibrium calculation of the low temperature
transport properties of a quantum dot in the Kondo regime when an AC potential
is applied to the gate voltage. We solve a time dependent Anderson model with
finite on-site Coulomb interaction. The interaction self-energy is calculated
up to second order in perturbation theory in the on-site interaction, in the
context of the Keldysh non-equilibrium technique, and the effect of the AC
voltage is taken into account exactly for all ranges of AC frequencies and AC
intensities. The obtained linear conductance and time-averaged density of
states of the quantum dot evolve in a non trivial way as a function of the AC
frequency and AC intensity of the harmonic modulation.Comment: 30 pages,7 figure
Non-equilibrium Kondo effect in asymmetrically coupled quantum dot
The quantum dot asymmetrically coupled to the external leads has been
analysed theoretically by means of the equation of motion (EOM) technique and
the non-crossing approximation (NCA). The system has been described by the
single impurity Anderson model. To calculate the conductance across the device
the non-equilibrium Green's function technique has been used. The obtained
results show the importance of the asymmetry of the coupling for the appearance
of the Kondo peak at nonzero voltages and qualitatively explain recent
experiments.Comment: 7 pages, 6 figures, Physical Review B (accepted for publication
Elucidation of the role of the complex in hydride transfer reaction between methylene blue and 1-benzyl-1,4-dihydronictinamide by effect of γ-cyclodextrin
The kinetics of the hydride transfer reaction between Methylene Blue (MB+) and 1-benzyl-1,4-dihydronicotinamide (BNAH) were studied in 10 % ethanol-90 % water mixed solvents containing β- and γ-cyclodextrins (β-CD and γ-CD). The pseudo-first order rate constant shows kinetic saturation at high initial concentration of BNAH. This indicates the formation of a complex between MB+ and BNAH. The reaction was suppressed by addition of β-CD, but enhanced by addition of γ-CD. MB+ and BNAH were separately accommodated within the β-CD cavity and the cavity walls may protect the activity site of the reactants. On the other hand, in the MB+-BNAH-γ-CD system, the inclusion of the complex between MB+ and BNAH with γ-CD occurred. This effect of γ-CD can distinguish between the productive and non-productive nature of the complex.</p
Study of the lineshape of the chi(c1) (3872) state
A study of the lineshape of the chi(c1) (3872) state is made using a data sample corresponding to an integrated luminosity of 3 fb(-1) collected in pp collisions at center-of-mass energies of 7 and 8 TeV with the LHCb detector. Candidate chi(c1)(3872) and psi(2S) mesons from b-hadron decays are selected in the J/psi pi(+)pi(-) decay mode. Describing the lineshape with a Breit-Wigner function, the mass splitting between the chi(c1 )(3872) and psi(2S) states, Delta m, and the width of the chi(c1 )(3872) state, Gamma(Bw), are determined to be (Delta m=185.598 +/- 0.067 +/- 0.068 Mev,)(Gamma BW=1.39 +/- 0.24 +/- 0.10 Mev,) where the first uncertainty is statistical and the second systematic. Using a Flatte-inspired model, the mode and full width at half maximum of the lineshape are determined to be (mode=3871.69+0.00+0.05 MeV.)(FWHM=0.22-0.04+0.13+0.07+0.11-0.06-0.13 MeV, ) An investigation of the analytic structure of the Flatte amplitude reveals a pole structure, which is compatible with a quasibound D-0(D) over bar*(0) state but a quasivirtual state is still allowed at the level of 2 standard deviations
Measurement of the CKM angle in and decays with
A measurement of -violating observables is performed using the decays
and , where the meson is
reconstructed in one of the self-conjugate three-body final states and (commonly denoted ). The decays are analysed in bins of the -decay phase space, leading
to a measurement that is independent of the modelling of the -decay
amplitude. The observables are interpreted in terms of the CKM angle .
Using a data sample corresponding to an integrated luminosity of
collected in proton-proton collisions at centre-of-mass
energies of , , and with the LHCb experiment,
is measured to be . The hadronic
parameters , , , and ,
which are the ratios and strong-phase differences of the suppressed and
favoured decays, are also reported
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