73,036 research outputs found
Modelling of Electroluminescence in Polymers Using a Bipolar Charge Transport Model
Electroluminescence (EL) in polymeric materials is thought to occur due to the energy dissipation process from the recombination of opposite polarity charge carriers. It is considered as an indication of storage and transport of charge carriers in cable insulation subject to electrical stresses and may indicate the change in charge movement due to aging or degradation processes. Under ac electric fields, the interaction of opposite polarity charge carriers at the interface of polymer/conductor is enhanced compared with dc conditions, and seems to contribute a lot to the electroluminescence rather than the charge behaviours in the bulk of polymers. The dynamics of charge carriers both at the interface of polymer/conductor and in the bulk of polymers is investigated through a simulation work using a bipolar charge transport model. Figure 1 compares experimental electroluminescence results with simulated data from the recombination of injected charge carriers. The paper will give more details on EL model and comparison under various waveforms and frequencies
Absence of Josephson coupling between certain superconductors
It is generally believed that superconductivity can occur in materials
irrespective of whether the charge carriers in the material are electrons or
holes. Here we point out that Josephson tunneling would not occur between
superconductors with charge carriers of opposite sign. Consequently,
observation of Josephson tunneling between two superconductors implies that
their charge carriers have the same sign. We propose that this has profound
implications for the understanding of superconductivity and in particular is
consistent with the theory of hole superconductivity
Differential Step Response of Unipolar Space-Charge-Limited Current in Solids
The small signal step response of unipolar space‐charge‐limited current in solids is analyzed for planar structures and for media in which the drift velocity of the charge carriers is either proportional to the electric field (thermal charge carriers) or is independent of the electric field (hot charge carriers). Results are reported in analytical and graphical form. Their features are discussed in terms of the underlying physical phenomena, as well as in the perspective of experimental applications. Cylindrical and spherical structures are not accessible to closed‐form solutions by the approach
Quantum transport of slow charge carriers in quasicrystals and correlated systems
We show that the semi-classical model of conduction breaks down if the mean
free path of charge carriers is smaller than a typical extension of their
wavefunction. This situation is realized for sufficiently slow charge carriers
and leads to a transition from a metallic like to an insulating like regime
when scattering by defects increases. This explains the unconventional
conduction properties of quasicrystals and related alloys. The conduction
properties of some heavy fermions or polaronic systems, where charge carriers
are also slow, present a deep analogy.Comment: 4 page
Magnetoresistance based determination of basic parameters of minority charge carriers in solid matter
Magnetoresistance as a tool of basic parameters determination of minority
charge carriers and the ratio of minority charge carriers conductivity to
majority ones in solid matter has been considered within the framework of the
phenomenological two-band model. The criterion of the application of this model
has been found. As examples of these equations usage the conductor,
semiconductor and superconductor have been introduced. From the obtained
temperature dependences of the aforementioned values in superconductor, a
supposition of a deciding role of minority charge carriers in the emergence of
superconductivity state has been made.Comment: 7 pages, 3 figures, 2 table
Zero modes on cosmic strings in an external magnetic field
A classical analysis suggests that an external magnetic field can cause
trajectories of charge carriers on a superconducting domain wall or cosmic
string to bend, thus expelling charge carriers with energy above the mass
threshold into the bulk. We study this process by solving the Dirac equation
for a fermion of mass and charge , in the background of a domain wall
and a magnetic field of strength . We find that the modes of the charge
carriers get shifted into the bulk, in agreement with classical expectations.
However the dispersion relation for the zero modes changes dramatically --
instead of the usual linear dispersion relation, , the new
dispersion relation is well fit by where
for a thin wall in the weak field limit, and for a thick
wall of width . This result shows that the energy of the charge carriers on
the domain wall remains below the threshold for expulsion even in the presence
of an external magnetic field. If charge carriers are expelled due to an
additional perturbation, they are most likely to be ejected at the threshold
energy .Comment: 9 pages, 4 figure
Optical conductivity of polaronic charge carriers
The optical conductivity of charge carriers coupled to quantum phonons is
studied in the framework of the one-dimensional spinless Holstein model. For
one electron, variational diagonalisation yields exact results in the
thermodynamic limit, whereas at finite carrier density analytical
approximations based on previous work on single-particle spectral functions are
obtained. Particular emphasis is put on deviations from weak-coupling,
small-polaron or one-electron theories occurring at intermediate coupling
and/or finite carrier density. The analytical results are in surprisingly good
agreement with exact data, and exhibit the characteristic polaronic excitations
observed in experiments on manganites.Comment: 23 pages, 11 figure
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