6,299 research outputs found
Pressure and temperature driven phase transitions in HgTe quantum wells
We present theoretical investigations of pressure and temperature driven
phase transitions in HgTe quantum wells grown on CdTe buffer. Using the 8-band
\textbf{kp} Hamiltonian we calculate evolution of energy band structure
at different quantum well width with hydrostatic pressure up to 20 kBar and
temperature ranging up 300 K. In particular, we show that in addition to
temperature, tuning of hydrostatic pressure allows to drive transitions between
semimetal, band insulator and topological insulator phases. Our realistic band
structure calculations reveal that the band inversion under hydrostatic
pressure and temperature may be accompanied by non-local overlapping between
conduction and valence bands. The pressure and temperature phase diagrams are
presented.Comment: 9 pages, 8 figures + Supplemental material (5 pages
Temperature-driven single-valley Dirac fermions in HgTe quantum wells
We report on temperature-dependent magnetospectroscopy of two HgTe/CdHgTe
quantum wells below and above the critical well thickness . Our results,
obtained in magnetic fields up to 16 T and temperature range from 2 K to 150 K,
clearly indicate a change of the band-gap energy with temperature. The quantum
well wider than evidences a temperature-driven transition from
topological insulator to semiconductor phases. At the critical temperature of
90 K, the merging of inter- and intra-band transitions in weak magnetic fields
clearly specifies the formation of gapless state, revealing the appearance of
single-valley massless Dirac fermions with velocity of
ms. For both quantum wells, the energies extracted from
experimental data are in good agreement with calculations on the basis of the
8-band Kane Hamiltonian with temperature-dependent parameters.Comment: 5 pages, 3 figures and Supplemental Materials (4 pages
Manganese catalysts to obtain olefins from C1-C4 alkanes
Oxidative transformations of C1-C4 alkanes into olefins on oxide manganese catalysts were under study. We also studied oxidative coupling of methane (OCM) into ethylene on deposited and applied on the silicon dioxide catalysts. We studied the influence of chemical composition of catalyst and promotors on the OCM. Adding a little amount of ethane and propane hydrocarbons to methane allows increasing the concentration of ethylene in gases and significantly increasing productivity in ethylene. The study also shows the impact of the amount of manganese and promotors applied on SiO2 on the yield of olefins during the conversion of C3-C4 alkanes
Statistical Moments and Scintillation Level of Scattered Electromagnetic Waves in the Magnetized plasma
Statistical characteristics of scattered ordinary and extraordinary electromagnetic waves in the magnetized plasma are considered using the smooth perturbation method. Diffraction effects and polarization coefficients are taken into account. Second order statistical moments of scattered radiation are obtained for arbitrary correlation function of electron density fluctuations. Broadening of the spatial power spectrum and displacement of its maximum, wave phase structure function and the angle-of-arrivals are obtained for three-dimensional spectral function containing anisotropic Gaussian and power-law spectral functions. Scintillation level of scattered radiation is analyzed for different parameters characterizing anisotropic plasma irregularities for the ionospheric F-region. The spectral widths (first and second moments) of the power spectrum and scintillation periods are calculated for “frozen-in” drifting elongated plasma irregularities using the experimental data
Modeling of contact interaction of a heated plane rigid elliptical punch with a transversally isotropic elastic half-space
On the base of a rigorous mathematical model, the problem of the contact interaction of a heated flat punch of an elliptical section with a transversely isotropic elastic half-space is investigated. It is assumed that the half-space surface is the isotropy plane of a transversely isotropic material, and also that there is a smooth (without friction) contact. Expressions of contact stresses and displacements of a heated flat elliptical punch are found explicitly. In the form of a simple inequality, a condition for separating the elastic material from the surface of a flat elliptical punch is obtained. Numerical calculations are carried out. Contact interaction of a heated flat punch is studied taking into account the separation of material from the punch
Temperature-dependent magnetospectroscopy of HgTe quantum wells
We report on magnetospectroscopy of HgTe quantum wells in magnetic fields up
to 45 T in temperature range from 4.2 K up to 185 K. We observe intra- and
inter-band transitions from zero-mode Landau levels, which split from the
bottom conduction and upper valence subbands, and merge under the applied
magnetic field. To describe experimental results, realistic
temperature-dependent calculations of Landau levels have been performed. We
show that although our samples are topological insulators at low temperatures
only, the signature of such phase persists in optical transitions at high
temperatures and high magnetic fields. Our results demonstrate that
temperature-dependent magnetospectroscopy is a powerful tool to discriminate
trivial and topological insulator phases in HgTe quantum wells
HERBARIUM SPECIMENS OF WILD CHILEAN POTATO SPECIES BELONGING TO THE SECTION <i> PETOTA </i> DUMORT. GENUS <i> SOLANUM </i> L. IN THE VIR HERBARIUM
A revision of herbarium specimens of Chilean potato species belonging to the section Petota Dumort. genus Solanum L. was conducted. The VIR herbarium [WIR] has 25 specimen sheets of five species: Solanum leptostigma Juz., S. maglia Schlechtd., S. molinae Juz., S. ochoanum Lechn., S. zykinii Lechn. Authentic materials from S.V. Yuzepczuk and V.S. Lehnovich have been identified, namely syntypes of S. molinae , S. ochoanum and S. zykinii. The neotypification of S. leptostigma was done
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