310 research outputs found
Pecularities of Hall effect in GaAs/{\delta}<Mn>/GaAs/In\timesGa1-\timesAs/GaAs (\times {\approx} 0.2) heterostructures with high Mn content
Transport properties of GaAs/{\delta}/GaAs/In\timesGa1-\timesAs/GaAs
structures containing InxGa1-xAs (\times {\approx} 0.2) quantum well (QW) and
Mn delta layer (DL) with relatively high, about one Mn monolayer (ML) content,
are studied. In these structures DL is separated from QW by GaAs spacer with
the thickness ds = 2-5 nm. All structures possess a dielectric character of
conductivity and demonstrate a maximum in the resistance temperature dependence
Rxx(T) at the temperature {\approx} 46K which is usually associated with the
Curie temperature Tc of ferromagnetic (FM) transition in DL. However, it is
found that the Hall effect concentration of holes pH in QW does not decrease
below TC as one ordinary expects in similar systems. On the contrary, the
dependence pH(T) experiences a minimum at T = 80-100 K depending on the spacer
thickness, then increases at low temperatures more strongly than ds is smaller
and reaches a giant value pH = (1-2)\cdot10^13 cm^(-2). Obtained results are
interpreted in the terms of magnetic proximity effect of DL on QW, leading to
induce spin polarization of the holes in QW. Strong structural and magnetic
disorder in DL and QW, leading to the phase segregation in them is taken into
consideration. The high pH value is explained as a result of compensation of
the positive sign normal Hall effect component by the negative sign anomalous
Hall effect component.Comment: 19 pages, 6 figure
Review of scientific topics for Millimetron space observatory
This paper describes outstanding issues in astrophysics and cosmology that
can be solved by astronomical observations in a broad spectral range from far
infrared to millimeter wavelengths. The discussed problems related to the
formation of stars and planets, galaxies and the interstellar medium, studies
of black holes and the development of the cosmological model can be addressed
by the planned space observatory Millimetron (the "Spectr-M" project) equipped
with a cooled 10-m mirror. Millimetron can operate both as a single-dish
telescope and as a part of a space-ground interferometer with very long
baseline.Comment: The translation of the original article in Physics Uspekhi
http://ufn.ru/ru/articles/2014/12/c
Structural and transport properties of GaAs/delta<Mn>/GaAs/InxGa1-xAs/GaAs quantum wells
We report results of investigations of structural and transport properties of
GaAs/Ga(1-x)In(x)As/GaAs quantum wells (QWs) having a 0.5-1.8 ML thick Mn
layer, separated from the QW by a 3 nm thick spacer. The structure has hole
mobility of about 2000 cm2/(V*s) being by several orders of magnitude higher
than in known ferromagnetic two-dimensional structures. The analysis of the
electro-physical properties of these systems is based on detailed study of
their structure by means of high-resolution X-ray diffractometry and
glancing-incidence reflection, which allow us to restore the depth profiles of
structural characteristics of the QWs and thin Mn containing layers. These
investigations show absence of Mn atoms inside the QWs. The quality of the
structures was also characterized by photoluminescence spectra from the QWs.
Transport properties reveal features inherent to ferromagnetic systems: a
specific maximum in the temperature dependence of the resistance and the
anomalous Hall effect (AHE) observed in samples with both "metallic" and
activated types of conductivity up to ~100 K. AHE is most pronounced in the
temperature range where the resistance maximum is observed, and decreases with
decreasing temperature. The results are discussed in terms of interaction of
2D-holes and magnetic Mn ions in presence of large-scale potential fluctuations
related to random distribution of Mn atoms. The AHE values are compared with
calculations taking into account its "intrinsic" mechanism in ferromagnetic
systems.Comment: 15 pages, 9 figure
Neutrino conversions in random magnetic fields and from the Sun
The magnetic field in the convective zone of the Sun has a random small-scale
component with the r.m.s. value substantially exceeding the strength of a
regular large-scale field. For two Majorana neutrino flavors two
helicities in the presence of a neutrino transition magnetic moment and nonzero
neutrino mixing we analyze the displacement of the allowed ()-parameter region reconciled for the SuperKamiokande(SK) and
radiochemical (GALLEX, SAGE, Homestake) experiments in dependence on the r.m.s.
magnetic field value , or more precisely, on a value assuming the
transition magnetic moment . In contrast to RSFP in
regular magnetic fields we find an effective production of electron
antineutrinos in the Sun even for small neutrino mixing through cascade
conversions , in a random magnetic field that would be a
signature of the Majorana nature of neutrino if will be
registered. Basing on the present SK bound on electron antineutrinos we have
also found an excluded area in the same -plane and
revealed a strong sensitivity to the random magnetic field correlation length
.Comment: LaTex 36 pages including 14 PostScript figure
The Design Optimization and Experimental Investigation of the 4.4 μm Raman Laser Basedon Hydrogen-filled Revolver Silica Fiber
Optical properties of hollow-core revolver fibers are numerically investigated depending on various parameters: the hollow-core diameter, the capillary wall thickness, the values of the minimum gap between the capillaries, the number of capillaries in the cladding and the type of glass (silica and chalcogenide). Preliminary, similar calculations are made for simple models of hollow-core fibers. Based on the obtained results, the optimal design of the revolver fiber for Raman laser frequency conversion (1.56 μm → 4.4 μm in 1H2) was determined. As a result, efficient ns-pulsed 4.42 μm Raman laser based on 1H2-filled revolver silica fiber is realized. Quantum efficiency as high as 36 % is achieved and output average power as high as 250 mW is demonstrated
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