817 research outputs found
Tailoring Chirp in Spin-Lasers
The usefulness of semiconductor lasers is often limited by the undesired
frequency modulation, or chirp, a direct consequence of the intensity
modulation and carrier dependence of the refractive index in the gain medium.
In spin-lasers, realized by injecting, optically or electrically,
spin-polarized carriers, we elucidate paths to tailoring chirp. We provide a
generalized expression for chirp in spin-lasers and introduce modulation
schemes that could simultaneously eliminate chirp and enhance the bandwidth, as
compared to the conventional (spin-unpolarized) lasers.Comment: 4 pages, 3 figure
Piezomagnetic Quantum Dots
We study the influence of deformations on magnetic ordering in quantum dots
doped with magnetic impurities. The reduction of symmetry and the associated
deformation from circular to elliptical quantum confinement lead to the
formation of piezomagnetic quantum dots. The strength of elliptical deformation
can be controlled by the gate voltage to change the magnitude of magnetization,
at a fixed number of carriers and in the absence of applied magnetic field. We
reveal a reentrant magnetic ordering with the increase of elliptical
deformation and suggest that the piezomagnetic quantum dots can be used as
nanoscale magnetic switches.Comment: 4 pages, 3 figure
Magnetoanisotropic Andreev Reflection in Ferromagnet/Superconductor Junctions
Andreev reflection spectroscopy of ferromagnet/superconductor (FS) junctions
is an important probe of spin polarization. We theoretically investigate
spin-polarized transport in FS junctions in the presence of Rashba and
Dresselhaus interfacial spin-orbit fields and show that Andreev reflection can
be controlled by changing the magnetization orientation. We predict a giant in-
and out-of-plane magnetoanisotropy of the junction conductance. If the
ferromagnet is highly spin polarized---in the half-metal limit---the
magnetoanisotropic Andreev reflection depends universally on the spin-orbit
fields only. Our results show that Andreev reflection spectroscopy can be used
for sensitive probing of interfacial spin-orbit fields in FS junction.Comment: Pages 6-10 contain supplemental materia
Probing topological transitions in HgTe/CdTe quantum wells by magneto-optical measurements
In two-dimensional topological insulators, such as inverted HgTe/CdTe quantum
wells, helical quantum spin Hall (QSH) states persist even at finite magnetic
fields below a critical magnetic field , above which only quantum
Hall (QH) states can be found. Using linear-response theory, we theoretically
investigate the magneto-optical properties of inverted HgTe/CdTe quantum wells,
both for infinite two-dimensional and finite-strip geometries, and possible
signatures of the transition between the QSH and QH regimes. In the absorption
spectrum, several peaks arise due to non-equidistant Landau levels in both
regimes. However, in the QSH regime, we find an additional absorption peak at
low energies in the finite-strip geometry. This peak arises due to the presence
of edge states in this geometry and persists for any Fermi level in the QSH
regime, while in the QH regime the peak vanishes if the Fermi level is situated
in the bulk gap. Thus, by sweeping the gate voltage, it is possible to
experimentally distinguish between the QSH and QH regimes due to this
signature. Moreover, we investigate the effect of spin-orbit coupling and
finite temperature on this measurement scheme.Comment: 14 pages, 13 figure
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