160 research outputs found
Circular photon drag effect in bulk tellurium
The circular photon drag effect is observed in a bulk semiconductor. The
photocurrent caused by a transfer of both translational and angular momenta of
light to charge carriers is detected in tellurium in the mid-infrared frequency
range. Dependencies of the photocurrent on the light polarization and on the
incidence angle agree with the symmetry analysis of the circular photon drag
effect. Microscopic models of the effect are developed for both intra- and
inter-subband optical absorption in the valence band of tellurium. The shift
contribution to the circular photon drag current is calculated. An observed
decrease of the circular photon drag current with increase of the photon energy
is explained by the theory for inter-subband optical transitions. Theoretical
estimates of the circular photon drag current agree with the experimental data.Comment: 8 pages, 4 figure
Terahertz radiation due to random grating coupled surface plasmon polaritons
We report on terahertz (THz) radiation under electrical pumping from a
degenerate semiconductor possessing an electron accumulation layer. In InN, the
random grating formed by topographical defects provides high-efficiency
coupling of surface plasmon polaritons supported by the accumulation layer to
the THz emission. The principal emission band occupies the 2-6 THz spectral
range. We establish a link between the shape of emission spectra and the
structural factor of the random grating and show that the change of slope of
power dependencies is characteristic for temperature-dependent plasmonic
mechanisms. The super-linear rise of a THz emission intensity on applied
electric power provides advantage of such materials in emission yield.Comment: 4 pages, 4 figure
Neotypification of Pleurocapsa fuliginosa and epitypification of P. minor (Pleurocapsales): resolving a polyphyletic cyanobacterial genus
Strains with complete morphological match to Pleurocapsa fuliginosa and P. minor were isolated from Oahu (Hawaii, USA), with another strain matching P. minor isolated from a wet rock face in Utah (USA). Phylogenetically these baeocyte and pseudofilament producing strains fell in a single well-supported clade among a number of pleurocapsalean strains. They were sister to a clade of baeocyte-producing strains that lack the ability to form pseudofilaments and likely belong in an as-yet-to- be-described genus. Strains putatively named Pleurocapsa are scattered throughout the Pleurocapsales and Chroococcales, indicating a need for clear definition of the genus so that revisionary work and alpha-level taxonomy can move forward. To satisfy this need, P. fuliginosa HA4302-MV1 and P. minor HA4230-MV1 were chosen as neotype and epitype, respectively, establishing the genus based on molecular sequence data. In addition to the distinctive morphology of the genus, all Pleuro- capsa species for which 16S-23S ITS regions are available have an unusually long, branched D5 helix at the termination of the ITS region. The sister clade of strains that lack the ability to form pseudofilaments also possess an unusually long and branched D5 helix as well, suggesting that this feature of the ITS region may be a family-level synapomorphy
Opto-Electronic Characterization of Three Dimensional Topological Insulators
We demonstrate that the terahertz/infrared radiation induced photogalvanic
effect, which is sensitive to the surface symmetry and scattering details, can
be applied to study the high frequency conductivity of the surface states in
(Bi1-xSbx)2Te3 based three dimensional (3D) topological insulators (TI). In
particular, measuring the polarization dependence of the photogalvanic current
and scanning with a micrometre sized beam spot across the sample, provides
access to (i) topographical inhomogeneity's in the electronic properties of the
surface states and (ii) the local domain orientation. An important advantage of
the proposed method is that it can be applied to study TIs at room temperature
and even in materials with a high electron density of bulk carriers.Comment: 6 pages, 4 figure
Spin photocurrents and circular photon drag effect in (110)-grown quantum well structures
We report on the study of spin photocurrents in (110)-grown quantum well
structures. Investigated effects comprise the circular photogalvanic effect and
so far not observed circular photon drag effect. The experimental data can be
described by an analytical expression derived from a phenomenological theory. A
microscopic model of the circular photon drag effect is developed demonstrating
that the generated current has spin dependent origin.Comment: 6 pages, 3 figure
CRIS – service for input, storage and analysis of the biodiversity data of the cryptogams
Here we describe Cryptogamic Russian Information System (CRIS), a web service cataloguing the biodiversity of cryptogams: cyanobacteria, fungi (including lichens), and bryophytes. CRIS incorporates a wide spectrum of data types, allowing for greater ease of use. It is possible to print the labels for herbarium collections, to input literature references, media files, etc., using CRIS which has a flexible interface and specific technical abilities. Currently, CRIS contains ~ 90,000 herbarium records, including 67,861 records of bryophytes, 12,486 records of lichens and 3,800 records of cyanobacteria. Data analysis of the different taxonomic groups is provided below. Perspectives and directions for the future development of CRIS are discussed
Helicity-dependent photocurrents in graphene layers excited by mid-infrared radiation of a CO-laser
We report the study of the helicity driven photocurrents in graphene excited
by mid-infrared light of a CO-laser. Illuminating an unbiased monolayer
sheet of graphene with circularly polarized radiation generates -- under
oblique incidence -- an electric current perpendicular to the plane of
incidence, whose sign is reversed by switching the radiation helicity. We show
that the current is caused by the interplay of the circular Hall effect
and the circular photogalvanic effect. Studying the frequency dependence of the
current in graphene layers grown on the SiC substrate we observe that the
current exhibits a resonance at frequencies matching the longitudinal optical
phonon in SiC
- …