2,814 research outputs found
Coulomb drag between one-dimensional conductors
We have analyzed Coulomb drag between currents of interacting electrons in
two parallel one-dimensional conductors of finite length attached to
external reservoirs. For strong coupling, the relative fluctuations of electron
density in the conductors acquire energy gap . At energies larger than
, where
is the impurity scattering rate, and for , where is the
fluctuation velocity, the gap leads to an ``ideal'' drag with almost equal
currents in the conductors. At low energies the drag is suppressed by coherent
instanton tunneling, and the zero-temperature transconductance vanishes,
indicating the Fermi liquid behavior.Comment: 5 twocolumn pages in RevTex, added 1 eps-Figure and calculation of
trans-resistanc
Fractional charge in transport through a 1D correlated insulator of finite length
Transport through a one channel wire of length confined between two leads
is examined when the 1D electron system has an energy gap : induced by the interaction in charge mode (: charge velocity in the
wire). In spinless case the transformation of the leads electrons into the
charge density wave solitons of fractional charge entails a non-trivial low
energy crossover from the Fermi liquid behavior below the crossover energy to the insulator one with the
fractional charge in current vs. voltage, conductance vs. temperature, and in
shot noise. Similar behavior is predicted for the Mott insulator of filling
factor .Comment: 5 twocolumn pages in RevTex, no figure
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
State of infantile mortality in Chernigov area.
State and dynamics of perinatal and infant mortality rate in Chernigov region over the 2001-2010 period were studied. It is shown that the level of perinatal mortality and mortinatality should be analysed separately over 2 periods: 2001-2006 and 2007-2010, as in 2007 Ukraine turned to determination of perinatal period, live birth - and mortinatality according to WHO criteria. It is identified that over the 2001-2006 period there were no considerable changes of perinatal mortality level in Chernigov region. Over the 2007-2010 period this index dropped by 14 %, while in Ukraine – only by 6,3 %. During 2001-2006 mortinatality in this area was lower than in Ukraine, however it had a tendency to increase (by 10,6%); in subsequent years this resulted in exceeding of national values. Level of mortinatality rate in Chernigov region over the 2001-2010 period dropped by 28,6%, while in Ukraine – by 19,5%. It is identified that decrease in level of mortinatality occurred due to the decline of both neonatal and postneonatal mortality rate. Ranking of region areas by the levels of perinatal mortality, mortinatality, infant mortality, including neonatal and postneonatal mortality was conducted. It is found that perinatal states, inborn anomalies and accidents are the main causes of infant mortality both in Chernigov region and in Ukraine as a whole. Over the 2004-2010 period proportion of perinatal states in the structure of infant mortality rate increased by 14,8 %
Zero-Point Fluctuations and the Quenching of the Persistent Current in Normal Metal Rings
The ground state of a phase-coherent mesoscopic system is sensitive to its
environment. We investigate the persistent current of a ring with a quantum dot
which is capacitively coupled to an external circuit with a dissipative
impedance. At zero temperature, zero-point quantum fluctuations lead to a
strong suppression of the persistent current with decreasing external
impedance. We emphasize the role of displacement currents in the dynamical
fluctuations of the persistent current and show that with decreasing external
impedance the fluctuations exceed the average persistent current.Comment: 4 pages, 2 eps figure
Density of states and zero Landau level probed through capacitance of graphene
We report capacitors in which a finite electronic compressibility of graphene
dominates the electrostatics, resulting in pronounced changes in capacitance as
a function of magnetic field and carrier concentration. The capacitance
measurements have allowed us to accurately map the density of states D, and
compare it against theoretical predictions. Landau oscillations in D are robust
and zero Landau level (LL) can easily be seen at room temperature in moderate
fields. The broadening of LLs is strongly affected by charge inhomogeneity that
leads to zero LL being broader than other levels
Modulation of radio frequency signals by ULF waves
The ionospheric plasma is continually perturbed by ultra-low frequency (ULF; 1&ndash;100 mHz) plasma waves that are incident from the magnetosphere. In this paper we present a combined experimental and modeling study of the variation in radio frequency of signals propagating in the ionosphere due to the interaction of ULF wave energy with the ionospheric plasma. Modeling the interaction shows that the magnitude of the ULF wave electric field, <B>e</B>, and the geomagnetic field, <B>B</B><sub>0</sub>, giving an <B>e</B>&times;<B>B</B><sub>0</sub> drift, is the dominant mechanism for changing the radio frequency. We also show how data from high frequency (HF) Doppler sounders can be combined with HF radar data to provide details of the spatial structure of ULF wave energy in the ionosphere. Due to spatial averaging effects, the spatial structure of ULF waves measured in the ionosphere may be quite different to that obtained using ground based magnetometer arrays. The ULF wave spatial structure is shown to be a critical parameter that determines how ULF wave effects alter the frequency of HF signals propagating through the ionosphere
Conductance of a Mott Quantum Wire
We consider transport through a one-dimensional conductor subject to an
external periodic potential and connected to non-interacting leads (a "Mott
quantum wire"). For the case of a strong periodic potential, the conductance is
shown to jump from zero, for the chemical potential lying within the
Mott-Hubbard gap, to the non-interacting value of 2e^2/h, as soon as the
chemical potential crosses the gap edge. This behavior is strikingly different
from that of an optical conductivity, which varies continuously with the
carrier concentration. For the case of a weak potential, the perturbative
correction to the conductance due to Umklapp scattering is absent away from
half-filling.Comment: 4 pages, RevTex, 1 ps figure included; published versio
- …