1,477 research outputs found
Transport properties of single channel quantum wires with an impurity: Influence of finite length and temperature on average current and noise
The inhomogeneous Tomonaga Luttinger liquid model describing an interacting
quantum wire adiabatically coupled to non-interacting leads is analyzed in the
presence of a weak impurity within the wire. Due to strong electronic
correlations in the wire, the effects of impurity backscattering, finite bias,
finite temperature, and finite length lead to characteristic non-monotonic
parameter dependencies of the average current. We discuss oscillations of the
non-linear current voltage characteristics that arise due to reflections of
plasmon modes at the impurity and quasi Andreev reflections at the contacts,
and show how these oscillations are washed out by decoherence at finite
temperature. Furthermore, the finite frequency current noise is investigated in
detail. We find that the effective charge extracted in the shot noise regime in
the weak backscattering limit decisively depends on the noise frequency
relative to , where is the Fermi velocity, the
Tomonaga Luttinger interaction parameter, and the length of the wire. The
interplay of finite bias, finite temperature, and finite length yields rich
structure in the noise spectrum which crucially depends on the
electron-electron interaction. In particular, the excess noise, defined as the
change of the noise due to the applied voltage, can become negative and is
non-vanishing even for noise frequencies larger than the applied voltage, which
are signatures of correlation effects.Comment: 28 pages, 19 figures, published version with minor change
PIH76 Children’s Medication In The Nordic Countries – Survey on National Administrative Register Data
Digitalitzat per Artypla
The tunnel magnetoresistance in chains of quantum dots weakly coupled to external leads
We analyze numerically the spin-dependent transport through coherent chains
of three coupled quantum dots weakly connected to external magnetic leads. In
particular, using the diagrammatic technique on the Keldysh contour, we
calculate the conductance, shot noise and tunnel magnetoresistance (TMR) in the
sequential and cotunneling regimes. We show that transport characteristics
greatly depend on the strength of the interdot Coulomb correlations, which
determines the spacial distribution of electron wave function in the chain.
When the correlations are relatively strong, depending on the transport regime,
we find both negative TMR as well as TMR enhanced above the Julliere value,
accompanied with negative differential conductance (NDC) and super-Poissonian
shot noise. This nontrivial behavior of tunnel magnetoresistance is associated
with selection rules that govern tunneling processes and various high-spin
states of the chain that are relevant for transport. For weak interdot
correlations, on the other hand, the TMR is always positive and not larger than
the Julliere TMR, although super-Poissonian shot noise and NDC can still be
observed
MATHEMATICAL MODELS PREDICTING LEUKOPENIA AND NEUTROPENIA IN PATIENTS WITH CHRONIC HEPATITIS C IN THE BACKGROUND INTERFERONCONTAINING SCHEMES
Currently in the Russian Federation or chronic hepatitis C (CHC) are still relevant Interferon-based regimens. The purpose of this study is to investigate the influence of baseline characteristics and prognosis of the patient HCV genotype 1 for the development of leukopenia (LP) and neutropenia (NP). We investigated factors such as sex, age, body mass index (BMI), viral load, genotype of Interleukin-28 B (IL-28B), the initial level of leukocytes and neutrophils, alanine aminotransferase (ALT), fibrosis, duration of infection, presence of previous therapy. Absolute values of leukocytes and neutrophils were analyzed on 4, 12, 24, 48 weeks of therapy, and at 4, 12, 24 weeks after antiviral treatment with protease inhibitors (PI) 1 and 2 generation. Prognostic criteria were identified, indicating the possible development of the LP and NP expressed during treatment with interferon: female gender, low initial load, TT-genotype of IL-28B, the initial level of white blood cells and neutrophils below 5,7×109/L and 3,4×109/L, respectively. Mathematical models predicting the onset of LP and NP, formalized in the form of decision trees were also constructed. These models have shown the greatest potential for practical use in view of highest accuracy and reliability
Andreev reflection in the fractional quantum Hall effect
We study the reflection of electrons and quasiparticles on point-contact
interfaces between fractional quantum Hall (FQH) states and normal metals
(leads), as well as interfaces between two FQH states with mismatched filling
fractions. We classify the processes taking place at the interface in the
strong coupling limit. In this regime a set of quasiparticles can decay into
quasiholes on the FQH side and charge excitations on the other side of the
junction. This process is analogous to an Andreev reflection in
normal-metal/superconductor (N-S) interfaces.Comment: 10 pages, 5 embedded EPS figures. Final version as published in Phys.
Rev. B 56, 2012 (1997
Electron transport in a quantum wire with realistic Coulomb interaction
Electron transport in a quantum wire with leads is investigated with actual
Coulomb interaction taken into account. The latter includes both the direct
interaction of electrons with each other and their interaction via the image
charges induced in the leads. Exact analytical solution of the problem is found
with the use of the bosonization technique for one-dimensional electrons and
three-dimensional Poisson equation for the electric field. The Coulomb
interaction is shown to change significantly the electron density distribution
along the wire as compared with the Luttinger liquid model with short-range
interactions. In DC and low frequency regimes, the Coulomb interaction causes
the charge density to increase strongly in the vicinity of the contacts with
the leads. The quantum wire impedance shows an oscillating behavior versus the
frequency caused by the resonances of the charge waves. The Coulomb interaction
produces a frequency dependent renormalization of the charge wave velocity.Comment: 10 two-colomn revtex pages, 6 postscript figures; one figure changed,
some typos corrected, to be published in Phys.Rev.
Probing Mechanical Properties of Graphene with Raman Spectroscopy
The use of Raman scattering techniques to study the mechanical properties of
graphene films is reviewed here. The determination of Gruneisen parameters of
suspended graphene sheets under uni- and bi-axial strain is discussed and the
values are compared to theoretical predictions. The effects of the
graphene-substrate interaction on strain and to the temperature evolution of
the graphene Raman spectra are discussed. Finally, the relation between
mechanical and thermal properties is presented along with the characterization
of thermal properties of graphene with Raman spectroscopy.Comment: To appear in the Journal of Materials Scienc
Interactions and Disorder in Multi-Channel Quantum Wires
Recent experiments have revealed that the temperature dependence of the
conductance of quasi-ballistic quantum wires bears clear features of the
Luttinger-liquid state. In this paper, the conductance of an N-channel quantum
wire is calculated within the model of N coupled Luttinger liquids and under
the assumption of weak disorder. It is shown that as the number of channels
increases, a crossover from the Luttinger-liquid to the Fermi-liquid behavior
occurs. This crossover manifests itself in the 1/N decrease of the scaling
exponent of the temperature dependence. An exact expression for the scaling
exponent for the case of N coupled Luttinger chains is obtained, and the large
N limit is studied for the case of a quantum wire. The case of N=2 for
electrons with spin is analyzed in detail, and a qualitative agreement with the
experiment is achieved.Comment: 9 pages, REVTex with 1 Postscript figur
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