154 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
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
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
Eye Hydrodynamics after Combined Treatment of Primary Open-Angle Glaucoma and Complicated Cataract
Aim: To study hydrodynamics of the eye after combined treatment – a combination of laser activation of trabecula and cataract phacoemulsification – in a comparative aspect.Material and methods. The study included 65 patients (65 eyes) with initial and advanced stages (I–II stages) of primary open-angle glaucoma (POAG) and complicated cataract. Among the patients there were 38 women (58.5 %) and 27 men (41.5 %), the average age was 68.8 ± 8.2 years. The follow-up period is 12 months after the treatment. The patients were divided into two groups: the main one – 33 patients (33 eyes) who underwent combined treatment – YAG-laser activation of trabecula (YAG-LAT) and phacoemulsification of cataract with intraocular lens (IOL) implantation, the control group – 32 patients (32 eyes) who underwent only phacoemulsification.Initially, the average intraocular pressure (IOP) (P0) in the main and control groups was 20.72 ± 3.39 mm Hg and 21.02 ± 3.55 mm Hg respectively. The average number of antihypertensive drugs used in the study group was 1.53 ± 0.64, in the control group – 1.34 ± 0.55.Results. There were no intraand postoperative complications. By the end of the follow-up period, a significant decrease in the average IOP level compared to its preoperative value by 29.2 % was determined in the main group, and 9.8 % in the control. The average number of antihypertensive drugs used in the study group decreased from 1.53 ± 0.64 to 0.67 ± 0.59 (p < 0.05), in the control group of patients, on the contrary, the average number of antihypertensive agents increased from 1.34 ± 0.55 to 1.91 ± 0.70 (p < 0.05).Conclusion. In the long-term postoperative period after combined treatment (YAG-LAT + phaco), IOP normalization was achieved in 96.9 % of cases, as well as a significant increase in visual acuity of patients. The developed method of treatment is safe, has a minimal risk of complications and can be used for the treatment of patients with initial stages of POAG in combination with complicated cataracts with increased IOP level, inefficiency of antihypertensive therapy
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
Application of synchrotron radiation to study the surface atomic structure of 2D materials
In this paper, the current state of X-ray photoelectron diffraction and holography methods are considered. A brief overview of surface research methods is given. The photoelectron diffraction method is attractive for use because of its sensitivity to the chemical environment, as well as its large depth of analysis (units of nanometers). The paper presents the application of methods for studying the atomic structure of bismuth chalcogenides Bi2X3 (X: Se,Te). The results of the holography were verified by theoretical modeling of diffraction patterns using the EDAC algorithm. © 2020 American Institute of Physics Inc. All rights reserved.The reported study was funded by RFBR, project number 19-29-12061 and was carried out within the state assignment of Ministry of Science and Higher Education of the Russian Federation (theme “Spin” No. АААА-А18-118020290104-2). L.V.Yashina acknowledges the support of her experimental work by RSF, grant 19-42-06303. We thank HZB for the allocation of synchrotron radiation beamtime
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