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

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

Fast detector of the ellipticity of infrared and terahertz radiation based on HgTe quantum well structures

We report a fast, room temperature detection scheme for the polarization ellipticity of laser radiation, with a bandwidth that stretches from the infrared to the terahertz range. The device consists of two elements, one in front of the other, that detect the polarization ellipticity and the azimuthal angle of the ellipse. The elements respectively utilise the circular photogalvanic effect in a narrow gap semiconductor and the linear photogalvanic effect in a bulk piezoelectric semiconductor. For the former we characterized both a HgTe quantum well and bulk Te, and for the latter, bulk GaAs. In contrast with optical methods our device is an easy to handle all-electric approach, which we demonstrated by applying a large number of different lasers from low power, continuous wave systems to high power, pulsed sources.Comment: 7 pages, 5 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

Impurity breakdown and terahertz luminescence in n-GaN epilayers under external electric field

We report on the observation and experimental studies of impurity breakdown and terahertz luminescence in n-GaN epilayers under external electric field. The terahertz electroluminescence is observed in a wide range of doping levels (at noncompensated donor density from 4.5×10[sup 16] to 3.4×10[sup 18] cm[sup −3]). Spectra of terahertz luminescence and photoconductivity are studied by means of Fourier transform spectrometry. Distinctive features of the spectra can be assigned to intracenter electron transitions between excited and ground states of silicon and oxygen donors and to hot electron transitions to the donor states.Peer reviewe

Characterization of Microbialites and Microbial Mats of the Laguna Negra Hypersaline Lake (Puna of Catamarca, Argentina)

Microbial carbonates provide an invaluable tool to understand biogeochemical processes in aqueous systems, especially in lacustrine and marine environments. Lakes are strongly sensitive to climatically driven environmental changes, and microbialites have recently been shown to provide a record of these changes. Unraveling physicochemical and microbiological controls on carbonates textures and geochemistry is necessary to correctly interpret these signals and the microbial biosphere record within sedimentary carbonates. The Laguna Negra is a high-altitude hypersaline Andean lake (Puna of Catamarca, Argentina), where abundant carbonate precipitation takes place and makes this system an interesting example that preserves a spectrum of carbonate fabrics reflecting complex physical, chemical, and biological interactions. The extreme environmental conditions (high UV radiation, elevated salinity, and temperature extremes) make the Laguna Negra a good analogue to some Precambrian microbialites (e.g., Tumbiana Fm., Archean, Australia). In addition, the discovery of ancient evaporating playa-lake systems on Mars’ surface (e.g., ShalbatanaVallis, Noachian, Mars) highlights the potential of Laguna Negra to provide insight into biosignature preservation in similar environments, in both terrestrial and extraterrestrial settings, given that microbial processes in the Laguna Negra can be studied with remarkable detail.Fil: Boidi, Flavia Jaquelina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Mlewski, Estela Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Gomez, Fernando Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Gérard, Emmanuelle. Centre National de la Recherche Scientifique; Franci

Atmospheric electrification in dusty, reactive gases in the solar system and beyond

Detailed observations of the solar system planets reveal a wide variety of local atmospheric conditions. Astronomical observations have revealed a variety of extrasolar planets none of which resembles any of the solar system planets in full. Instead, the most massive amongst the extrasolar planets, the gas giants, appear very similar to the class of (young) Brown Dwarfs which are amongst the oldest objects in the universe. Despite of this diversity, solar system planets, extrasolar planets and Brown Dwarfs have broadly similar global temperatures between 300K and 2500K. In consequence, clouds of different chemical species form in their atmospheres. While the details of these clouds differ, the fundamental physical processes are the same. Further to this, all these objects were observed to produce radio and X-ray emission. While both kinds of radiation are well studied on Earth and to a lesser extent on the solar system planets, the occurrence of emission that potentially originate from accelerated electrons on Brown Dwarfs, extrasolar planets and protoplanetary disks is not well understood yet. This paper offers an interdisciplinary view on electrification processes and their feedback on their hosting environment in meteorology, volcanology, planetology and research on extrasolar planets and planet formation