2,363 research outputs found
High-frequency oscillations in low-dimensional conductors and semiconductor superlattices induced by current in stack direction
A narrow energy band of the electronic spectrum in some direction in
low-dimensional crystals may lead to a negative differential conductance and
N-shaped I-V curve that results in an instability of the uniform stationary
state. A well-known stable solution for such a system is a state with electric
field domain. We have found a uniform stable solution in the region of negative
differential conductance. This solution describes uniform high-frequency
voltage oscillations. Frequency of the oscillation is determined by antenna
properties of the system. The results are applicable also to semiconductor
superlattices.Comment: 8 pages, 3 figure
Superlattice with hot electron injection: an approach to a Bloch oscillator
A semiconductor superlattice with hot electron injection into the miniband is
considered. The injection changes the stationary distribution function and
results in a qualitative change of the frequency behaviour of the differential
conductivity. In the regime with Bloch oscillating electrons and injection into
the upper part of the miniband the region of negative differential conductivity
is shifted from low frequencies to higher frequencies. We find that the dc
differential conductivity can be made positive and thus the domain instability
can be suppressed. At the same time the high-frequency differential
conductivity is negative above the Bloch frequency. This opens a new way to
make a Bloch oscillator operating at THz frequencies.Comment: RevTeX, 8 pages, 2 figures, to be published in Phys. Rev. B, 15
Januar 200
Prediction for new magnetoelectric fluorides
We use symmetry considerations in order to predict new magnetoelectric
fluorides. In addition to these magnetoelectric properties, we discuss among
these fluorides the ones susceptible to present multiferroic properties. We
emphasize that several materials present ferromagnetic properties. This
ferromagnetism should enhance the interplay between magnetic and dielectric
properties in these materials.Comment: 12 pages, 4 figures, To appear in Journal of Physics: Condensed
Matte
Exciton spin decay modified by strong electron-hole exchange interaction
We study exciton spin decay in the regime of strong electron-hole exchange
interaction. In this regime the electron spin precession is restricted within a
sector formed by the external magnetic field and the effective exchange fields
triggered by random spin flips of the hole. Using Hanle effect measurements, we
demonstrate that this mechanism dominates our experiments in CdTe/(Cd,Mg)Te
quantum wells. The calculations provide a consistent description of the
experimental results, which is supported by independent measurements of the
parameters entering the model.Comment: 5 pages, 3 figure
Spin Josephson effect in ferromagnet/ferromagnet tunnel junctions
We consider the tunnel spin current between two ferromagnetic metals from a
perspective similar to the one used in superconductor/superconductor tunnel
junctions. We use fundamental arguments to derive a Josephson-like spin tunnel
current . Here the phases are
associated with the planar contribution to the magnetization,
. The crucial step in our
analysis is the fact that the -component of the spin is canonically
conjugate to the phase of the planar contribution: . This is
analogous to the commutation relation in superconductors, where
is the phase associated to the superconducting order parameter and
is the Cooper pair number operator. We briefly discuss the experimental
consequences of our theoretical analysis.Comment: LaTex, seven pages, no figures; version to appear in Europhys. Lett.;
in order to make room for a more extended microscopic analysis, the
phenomenological discussion contained in v2 was remove
- …