1,738 research outputs found
Effects of different geometries on the conductance, shot noise and tunnel magnetoresistance of double quantum dots
The spin-polarized transport through a coherent strongly coupled double
quantum dot (DQD) system is analyzed theoretically in the sequential and
cotunneling regimes. Using the real-time diagrammatic technique, we analyze the
current, differential conductance, shot noise and tunnel magnetoresistance
(TMR) as a function of both the bias and gate voltages for double quantum dots
coupled in series, in parallel as well as for T-shaped systems. For DQDs
coupled in series, we find a strong dependence of the TMR on the number of
electrons occupying the double dot, and super-Poissonian shot noise in the
Coulomb blockade regime. In addition, for asymmetric DQDs, we analyze transport
in the Pauli spin blockade regime and explain the existence of the leakage
current in terms of cotunneling and spin-flip cotunneling-assisted sequential
tunneling. For DQDs coupled in parallel, we show that the transport
characteristics in the weak coupling regime are qualitatively similar to those
of DQDs coupled in series. On the other hand, in the case of T-shaped quantum
dots we predict a large super-Poissonian shot noise and TMR enhanced above the
Julliere value due to increased occupation of the decoupled quantum dot. We
also discuss the possibility of determining the geometry of the double dot from
transport characteristics. Furthermore, where possible, we compare our results
with existing experimental data on nonmagnetic systems and find qualitative
agreement.Comment: 15 pages, 12 figures, accepted in Phys. Rev.
Spin-polarized transport through weakly coupled double quantum dots in the Coulomb-blockade regime
We analyze cotunneling transport through two quantum dots in series weakly
coupled to external ferromagnetic leads. In the Coulomb blockade regime the
electric current flows due to third-order tunneling, while the second-order
single-barrier processes have indirect impact on the current by changing the
occupation probabilities of the double dot system. We predict a zero-bias
maximum in the differential conductance, whose magnitude is conditioned by the
value of the inter-dot Coulomb interaction. This maximum is present in both
magnetic configurations of the system and results from asymmetry in cotunneling
through different virtual states. Furthermore, we show that tunnel
magnetoresistance exhibits a distinctively different behavior depending on
temperature, being rather independent of the value of inter-dot correlation.
Moreover, we find negative TMR in some range of the bias voltage.Comment: 9 pages, 7 figures, accepted in Phys. Rev.
Canonical representation for electrons and its application to the Hubbard model
A new representation for electrons is introduced, in which the electron
operators are written in terms of a spinless fermion and the Pauli operators.
This representation is canonical, invertible and constraint-free. Importantly,
it simplifies the Hubbard interaction. On a bipartite lattice, the Hubbard
model is reduced to a form in which the exchange interaction emerges simply by
decoupling the Pauli subsystem from the spinless fermion bath. This exchange
correctly reproduces the large superexchange. Also derived, for
, is the Hamiltonian to study Nagaoka ferromagnetism. In this
representation, the infinite- Hubbard problem becomes elegant and easier to
handle. Interestingly, the ferromagnetism in Hubbard model is found to be
related to the gauge invariance of the spinless fermions. Generalization of
this representation for the multicomponent fermions, a new representation for
bosons, the notion of a `soft-core' fermion, and some interesting unitary
transformations are introduced and discussed in the appendices.Comment: 10+ pages, 3 Figure
Results of subionospheric radio LF monitoring prior to the Tokachi (M=8, Hokkaido, 25 September 2003) earthquake
International audienceResults of simultaneous LF subionospheric monitoring over two different propagation paths prior to the very strong Tokachi earthquake (near the east coast of Hokkaido Island, 25 September 2003) of magnitude 8.3 are presented firstly. Nighttime amplitude fluctuations of the Japanese Time Standard Transmitter (JG2AS, 40kHz) signal received at Moshiri (Japan, 142°E, 44°N) and at Petropavlovsk-Kamchatski (Russia, 158°E, 53°N) were analyzed. As a possible precursory signature we observed synchronous intensification of quasi periodical 16-day variations of the dispersion in the signals received at both observation stations before the earthquake. The strongest deviations observed as a rule were depletions of signal amplitude probably connected with increase of loss in the ionosphere by the enhancement of turbulence. This is due to dissipation of internal gravity waves (IGW) at the lower ionosphere heights. A scheme for seismo-IGW-planetary waves (PW) interconnection has been justified to explain the observed connection with strong earthquakes. It considers the seasonal variability in the signal
Subionospheric LF monitoring of ionospheric perturbations prior to the Tokachi-oki earthquake and a possible mechanism of lithosphere-ionosphere coupling
We first present the results of simultaneous monitoring of subionospheric LF propagation over two different paths prior to a very strong Tokachi-oki earthquake (near the east coast of Hokkaido Island on September 25, 2003) with magnitude 8.3. Nighttime amplitude fluctuations of the Japanese Time Standard Transmitter (JJY, 40 kHz) signal received at Moshiri (Japan, geographic coordinates 44°N, 142°E) and at Petropavlovsk-Kamchatski, Russia (53°N, 158°E) were analyzed. As a possible precursory signature we observed synchronous intensification of quasi-periodic 16-day variations of the dispersion in the signals received at both observation stations before the earthquake. The strongest deviations observed as a rule were depletions of signal amplitude probably connected with an increase in loss in the ionosphere by the enhancement of turbulence. This is due to dissipation of internal gravity waves (IGW) at the lower ionospheric heights. A scenario of interconnection between seismo-activity, atmospheric gravity waves and planetary waves, is proposed to explain the observed association with strong earthquakes
Results of subionospheric radio LF monitoring prior to the Tokachi (M=8, Hokkaido, 25 September 2003) earthquake
Guatemala: Village church, Church of PatzunColorVolume 92, Page
Suppression of superconductivity in granular metals
We investigate the suppression of the superconducting transition temperature
due to Coulomb repulsion in granular metallic systems at large tunneling
conductance between the grains, . We find the correction to the
superconducting transition temperature for 3 granular samples and films. We
demonstrate that depending on the parameters of superconducting grains, the
corresponding granular samples can be divided into two groups: (i) the granular
samples that belong to the first group may have only insulating or
superconducting states at zero temperature depending on the bare intergranular
tunneling conductance , while (ii) the granular samples that belong to the
second group in addition have an intermediate metallic phase where
superconductivity is suppressed while the effects of the Coulomb blockade are
not yet strong.Comment: 4 pages, 3 figure
Results of subionospheric radio LF monitoring prior to the Tokachi (M=8, Hokkaido, 25 September 2003) earthquake
Results of simultaneous LF subionospheric monitoring over two different propagation paths prior to the very strong Tokachi earthquake (near the east coast of Hokkaido Island, 25 September 2003) of magnitude 8.3 are presented firstly. Nighttime amplitude fluctuations of the Japanese Time Standard Transmitter (JG2AS, 40kHz) signal received at Moshiri (Japan, 142°E, 44°N) and at Petropavlovsk-Kamchatski (Russia, 158°E, 53°N) were analyzed. As a possible precursory signature we observed synchronous intensification of quasi periodical 16-day variations of the dispersion in the signals received at both observation stations before the earthquake. The strongest deviations observed as a rule were depletions of signal amplitude probably connected with increase of loss in the ionosphere by the enhancement of turbulence. This is due to dissipation of internal gravity waves (IGW) at the lower ionosphere heights. A scheme for seismo-IGW-planetary waves (PW) interconnection has been justified to explain the observed connection with strong earthquakes. It considers the seasonal variability in the signal
Ground-state properties of the one-dimensional electron liquid
We present calculations of the energy, pair-correlation function (PCF), static structure factor (SSF), and momentum density (MD) for the one-dimensional electron gas using the quantum Monte Carlo method. We are able to resolve peaks in the SSF at even-integer multiples of the Fermi wave vector, which grow as the coupling is increased. Our MD results show an increase in the effective Fermi wave vector as the interaction strength is raised in the paramagnetic harmonic wire; this appears to be a result of the vanishing difference between the wave functions of the paramagnetic and ferromagnetic systems. We have extracted the Luttinger liquid exponent from our MDs by fitting to data around kF, finding good agreement between the exponent of the ferromagnetic infinitely thin wire and the ferromagnetic harmonic wire
Diode Effect in Asymmetric Double Tunnel Barriers with Single Metal Nanoclusters
Asymmetric double tunnel barriers with the center electrode being a metal
cluster in the quantum regime are studied. The zero dimensionality of the
clusters used and the associated quantized energy spectra are manifest in
well-defined steps in the current voltage characteristic (IVC). Record high
current rectification ratios of 10000 for tunneling through such clusters are
demonstrated at room temperature. We are able to account for all of the
experimentally observed features by modeling our double barrier structures
using a combination of discrete states and charging effects for tunneling
through quantum dots.Comment: 8 pages and 3 figures. Accepted for publication in Applied Physics
Letters in 15 march 200
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