205 research outputs found
Laser-induced persistent photovoltage on the surface of a ternary topological insulator at room temperature
Using time- and angle-resolved photoemission, we investigate the ultrafast
response of excited electrons in the ternary topological insulator (BiSb)Te to fs-infrared pulses. We demonstrate that at the
critical concentration =0.55, where the system becomes bulk insulating, a
surface voltage can be driven at room temperature through the topological
surface state solely by optical means. We further show that such a photovoltage
persists over a time scale that exceeds 6 s, i.e, much longer than
the characteristic relaxation times of bulk states. We attribute the origin of
the photovoltage to a laser-induced band-bending effect which emerges near the
surface region on ultrafast time scales. The photovoltage is also accompanied
by a remarkable increase in the relaxation times of excited states as compared
to undoped topological insulators. Our findings are relevant in the context of
applications of topological surface states in future optical devices.Comment: 5 pages, 4 figure
Ultrafast spin polarization control of Dirac fermions in topological insulators
Three-dimensional topological insulators (TIs) are characterized by
spin-polarized Dirac-cone surface states that are protected from backscattering
by time-reversal symmetry. Control of the spin polarization of topological
surface states (TSSs) using femtosecond light pulses opens novel perspectives
for the generation and manipulation of dissipationless surface spin currents on
ultrafast timescales. Using time-, spin-, and angle-resolved spectroscopy, we
directly monitor for the first time the ultrafast response of the spin
polarization of photoexcited TSSs to circularly-polarized femtosecond pulses of
infrared light. We achieve all-optical switching of the transient out-of-plane
spin polarization, which relaxes in about 1.2 ps. Our observations establish
the feasibility of ultrafast optical control of spin-polarized Dirac fermions
in TIs and pave the way for novel optospintronic applications at ultimate
speeds.Comment: 9 pages, 4 figure
Implementing environmental culture in the language learning laboratory
© Canadian Center of Science and Education. The article deals with the description of the experimental work aimed at testing the effectiveness of the pedagogical conditions used in the environmental education of senior pupils by means of a foreign language. It is worth mentioning that during the experiment under the detection of the formation of the environmental education of senior pupils were identified the indicators by which we understand the environmental characteristics of the personality traits. The results were derived from the methods used in the process of the experiment, such as: conversation, testing, verification of empirical skills, analysis and synthesis. On the whole the difference in the results of the experimental groups significantly allows us to state the effectiveness of pedagogical conditions of the environmental education of senior pupils by means of a foreign language
Double Fe-impurity charge state in the topological insulator BiSe
The influence of individual impurities of Fe on the electronic properties of
topological insulator BiSe is studied by Scanning Tunneling Microscopy.
The microscope tip is used in order to remotely charge/discharge Fe impurities.
The charging process is shown to depend on the impurity location in the
crystallographic unit cell, on the presence of other Fe impurities in the close
vicinity, as well as on the overall doping level of the crystal. We present a
qualitative explanation of the observed phenomena in terms of tip-induced local
band bending. Our observations evidence that the specific impurity neighborhood
and the position of the Fermi energy with respect to the Dirac point and bulk
bands have both to be taken into account when considering the electron
scattering on the disorder in topological insulators.Comment: 10 pages, accepted for publication in Applied Physics Letters, minor
bugs were correcte
Photoemission of BiSe with Circularly Polarized Light: Probe of Spin Polarization or Means for Spin Manipulation?
Topological insulators are characterized by Dirac cone surface states with
electron spins aligned in the surface plane and perpendicular to their momenta.
Recent theoretical and experimental work implied that this specific spin
texture should enable control of photoelectron spins by circularly polarized
light. However, these reports questioned the so far accepted interpretation of
spin-resolved photoelectron spectroscopy. We solve this puzzle and show that
vacuum ultraviolet photons (50-70 eV) with linear or circular polarization
probe indeed the initial state spin texture of BiSe while circularly
polarized 6 eV low energy photons flip the electron spins out of plane and
reverse their spin polarization. Our photoemission calculations, considering
the interplay between the varying probing depth, dipole selection rules and
spin-dependent scattering effects involving initial and final states explain
these findings, and reveal proper conditions for light-induced spin
manipulation. This paves the way for future applications of topological
insulators in opto-spintronic devices.Comment: Submitted for publication (2013
Anisotropic effect of warping on the lifetime broadening of topological surface states in angle-resolved photoemission from Bi2 Te3
We analyze the strong hexagonal warping of the Dirac cone of Bi2Te3 by angle-
resolved photoemission. Along Γ¯¯¯M¯¯¯, the dispersion deviates from a linear
behavior meaning that the Dirac cone is warped outwards and not inwards. We
show that this introduces an anisotropy in the lifetime broadening of the
topological surface state which is larger along Γ¯¯¯K¯¯¯. The result is not
consistent with an explanation by nesting properties. Based on the
theoretically predicted modifications of the ground-state spin texture of a
strongly warped Dirac cone, we propose spin-dependent scattering processes as
explanation for the anisotropic scattering rates. These results could help
paving the way for optimizing future spintronic devices using topological
insulators and controlling surface-scattering processes via external gate
voltages
Co-Circulation of Coronaviruses among Rodents and Insectivores
Coronaviruses (family Coronaviridae, genera Alphacoronavirus and Betacoronavirus) are the causative agents of respiratory, intestinal and neurological diseases in humans and animals. Natural reservoirs of coronaviruses include bats, rodents and insectivores, however, the circulation of coronaviruses among rodents and insectivores in the Russian Federation has been unexplored. The aim of the study was to investigate the diversity of coronaviruses among rodents and insectivores co-inhabiting natural biotopes. Materials and methods. Rodents (68 specimens) and shrews of the genus Sorex (23 specimens) were caught in a limited forest area not exceeding 1.5 sq. km, in the vicinity of Novosibirsk. All samples were screened using reverse transcription polymerase chain reaction followed by sequencing. Results and discussion. Four distinct coronaviruses have been detected in four species of small mammals. Rodent-borne coronaviruses were classed within subgenera Embecovirus, genus Betacoronavirus, and demonstrated host-associated phylogenetic clustering. The level of homology between the new RNA isolates from red-backed vole (Myodes rutilus), root vole (Microtus oeconomus) and field mouse (Apodemus agrarius) is 85.5–87.7 %. The nucleotide sequences of Siberian coronavirus isolates are closely related (>93 % homology) to previously published sequences in each of the carrier groups found in Europe and China, which suggests their common evolutionary origin. The coronavirus identified in the common shrew (Sorex araneus) belongs to the genus Alphacoronavirus, but is significantly different (>36 % difference) from earlier identified strains included in the genus. It has been shown that different coronaviruses co-circulate in a limited area among rodents and insectivores
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