1,111 research outputs found
High-temperature excess current and quantum suppression of electronic backscattering in a 1-D system
We consider the electronic current through a one-dimensional conductor in the
ballistic transport regime and show that the quantum oscillations of a weakly
pinned single scattering target results in a temperature- and bias-voltage
independent excess current at large bias voltages. This is a genuine effect on
transport that derives from an exponential reduction of electronic
backscattering in the elastic channel due to quantum delocalization of the
scatterer and from suppression of low-energy electron backscattering in the
inelastic channels caused by the Pauli exclusion principle. We show that both
the mass of the target and the frequency of its quantum vibrations can be
measured by studying the differential conductance and the excess current. We
apply our analysis to the particular case of a weakly pinned C60 molecule
encapsulated by a single-wall carbon nanotube and find that the discussed
phenomena are experimentally observable.Comment: 4 pages, 4 figure
The Influence of Electro-Mechanical Effects on Resonant Electron Tunneling Through Small Carbon Nano-Peapods
The influence of a fullerene molecule trapped inside a single-wall carbon
nanotube on resonant electron transport at low temperatures and strong
polaronic coupling is theoretically discussed. Strong peak to peak fluctuations
and anomalous temperature behavior of conductance amplitudes are predicted and
investigated. The influence of the chiral properties of carbon nanotubes on
transport is also studied.Comment: 17 pages, 3 figures. Replaced with published version. Important
changes. Open access: http://stacks.iop.org/1367-2630/10/04304
Coherent and sequential photoassisted tunneling through a semiconductor double barrier structure
We have studied the problem of coherent and sequential tunneling through a
double barrier structure, assisted by light considered to be present All over
the structure, i,e emitter, well and collector as in the experimental evidence.
By means of a canonical transformation and in the framework of the time
dependent perturbation theory, we have calculated the transmission coefficient
and the electronic resonant current. Our calculations have been compared with
experimental results turning out to be in good agreement. Also the effect on
the coherent tunneling of a magnetic field parallel to the current in the
presence of light, has been considered.Comment: Revtex3.0, 8figures uuencoded compressed tar-fil
Theory of Thermoelectric Power in High-Tc Superconductors
We present a microscopic theory for the thermoelectric power (TEP) in high-Tc
cuprates. Based on the general expression for the TEP, we perform the
calculation of the TEP for a square lattice Hubbard model including all the
vertex corrections necessary to satisfy the conservation laws. In the present
study, characteristic anomalous temperature and doping dependences of the TEP
in high-Tc cuprates, which have been a long-standing problem of high-Tc
cuprates, are well reproduced for both hole- and electron-doped systems, except
for the heavily under-doped case. According to the present analysis, the strong
momentum and energy dependences of the self-energy due to the strong
antiferromagnetic fluctuations play an essential role in reproducing
experimental anomalies of the TEP.Comment: 5 pages, 8 figures, to appear in J. Phys. Soc. Jpn. 70 (2001) No.10.
Figure 2 has been revise
Giant lasing effect in magnetic nanoconductors
We propose a new principle for a compact solid-state laser in the 1-100 THz
regime. This is a frequency range where attempts to fabricate small size lasers
up till now have met severe technical problems. The proposed laser is based on
a new mechanism for creating spin-flip processes in ferromagnetic conductors.
The mechanism is due to the interaction of light with conduction electrons; the
interaction strength, being proportional to the large exchange energy, exceeds
the Zeeman interaction by orders of magnitude. On the basis of this
interaction, a giant lasing effect is predicted in a system where a population
inversion has been created by tunneling injection of spin-polarized electrons
from one ferromagnetic conductor to another -- the magnetization of the two
ferromagnets having different orientations. Using experimental data for
ferromagnetic manganese perovskites with nearly 100% spin polarization we show
the laser frequency to be in the range 1-100 THz. The optical gain is estimated
to be of order 10^7 cm^{-1}, which exceeds the gain of conventional
semiconductor lasers by 3 or 4 orders of magnitude. A relevant experimental
study is proposed and discussed.Comment: 4 pages, 3 figure
Analytical expressions for the charge-charge local-field factor and the exchange-correlation kernel of a two-dimensional electron gas
We present an analytical expression for the static many-body local field
factor of a homogeneous two-dimensional electron gas, which
reproduces Diffusion Monte Carlo data and embodies the exact asymptotic
behaviors at both small and large wave number . This allows us to also
provide a closed-form expression for the exchange and correlation kernel
, which represents a key input for density functional studies of
inhomogeneous systems.Comment: 5 pages, 3 figure
Noise in a Quantum Point Contact due to a Fluctuating Impurity Configuration
We propose a theoretical model for the low-frequency noise observed in a
quantum point contact (QPC) electrostatically defined in the 2D electron gas at
a GaAs-AlGaAs interface. In such contacts electron scattering by soft impurity-
or boundary potentials coherently splits an incoming wave function between
different transverse modes. Interference between these modes have been
suggested to explain observed non-linearities in the QPC-conductance. In this
study we invoke the same mechanism and the time-dependent current due to soft
dynamical impurity scattering in order to analyze the low-frequency
(telegraph-like) noise which has been observed along with a nonlinear
conductance. For the simplified case of a channel with two extended (current
carrying) modes, a simple analytical formula for the noise intensity is
derived. Generally we have found qualitative similarities between the noise and
the square of the transconductance. Nevertheless, incidentally there may be
situations when noise is suppressed but transconductance enhanced.Comment: 9 revte
Diffusion Thermopower at Even Denominator Fractions
We compute the electron diffusion thermopower at compressible Quantum Hall
states corresponding to even denominator fractions in the framework of the
composite fermion approach. It is shown that the deviation from the linear low
temperature behavior of the termopower is dominated by the logarithmic
temperature corrections to the conductivity and not to the thermoelectric
coefficient, although such terms are present in both quantities. The enhanced
magnitude of this effect compared to the zero field case may allow its
observation with the existing experimental techniques.Comment: Latex, 12 pages, Nordita repor
Influence of Long-Range Coulomb Interactions on the Metal-Insulator Transition in One-Dimensional Strongly Correlated Electron Systems
The influence of long-range Coulomb interactions on the properties of
one-dimensional (1D) strongly correlated electron systems in vicinity of the
metal-insulator phase transition is considered. It is shown that unscreened
repulsive Coulomb forces lead to the formation of a 1D Wigner crystal in the
metallic phase and to the transformation of the square-root singularity of the
compressibility (characterizing the commensurate-incommensurate transition) to
a logarithmic singularity. The properties of the insulating (Mott) phase depend
on the character of the short-wavelength screening of the Coulomb forces. For a
sufficiently short screening length the characteristics of the charge
excitations in the insulating phase are totally determined by the Coulomb
interaction and these quasipartic les can be described as quasiclassical
Coulomb solitons.Comment: 14 pages, LaTeX, G{\"o}teborg preprint APR 94-3
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