Transport in three-dimensional topological insulators: theory and experiment

This article reviews recent theoretical and experimental work on transport due to the surface states of three-dimensional topological insulators. The theoretical focus is on longitudinal transport in the presence of an electric field, including Boltzmann transport, quantum corrections and weak localization, as well as longitudinal and Hall transport in the presence of both electric and magnetic fields and/or magnetizations. Special attention is paid to transport at finite doping, to the $\pi$-Berry phase, which leads to the absence of backscattering, Klein tunneling and half-quantized Hall response. Signatures of surface states in ordinary transport and magnetotransport are clearly identified. The review also covers transport experiments of the past years, reviewing the initial obscuring of surface transport by bulk transport, and the way transport due to the surface states has increasingly been identified experimentally. Current and likely future experimental challenges are given prominence and the current status of the field is assessed.Comment: Review article to appear in Physica

Spin-helical transport in normal and superconducting topological insulators

In a topological insulator (TI) the character of electron transport varies from insulating in the interior of the material to metallic near its surface. Unlike, however, ordinary metals, conducting surface states in TIs are topologically protected and characterized by spin helicity whereby the direction of the electron spin is locked to the momentum direction. In this paper we review selected topics regarding recent theoretical and experimental work on electron transport and related phenomena in two-dimensional (2D) and three-dimensional (3D) TIs. The review provides a focused introductory discussion of the quantum spin Hall effect in HgTe quantum wells as well as transport properties of 3DTIs such as surface weak antilocalization, the half-integer quantum Hall effect, s + p-wave induced superconductivity, superconducting Klein tunneling, topological Andreev bound states and related Majorana midgap states. These properties of TIs are of practical interest, guiding the search for the routes towards topological spin electronics.Comment: Invited Topical Review on electron transport in 2D and 3D topological insulators, with focus on the quantum spin-Hall effect, weak antilocalization, half-integer quantum Hall effect, s- and p-wave induced superconductivity and superconducting Klein tunneling; 18 pages, 14 figures; accepted for publication in Physica Status Solidi

Planar Hall effect from the surface of topological insulators

A prominent feature of topological insulators (TIs) is the surface states comprising of spin-nondegenerate massless Dirac fermions. Recent technical advances have made it possible to address the surface transport properties of TI thin films by tuning the Fermi levels of both top and bottom surfaces. Here we report our discovery of a novel planar Hall effect (PHE) from the TI surface, which results from a hitherto-unknown resistivity anisotropy induced by an in-plane magnetic field. This effect is observed in dual-gated devices of bulk-insulating Bi2−x Sb x Te3 thin films, where the field-induced anisotropy presents a strong dependence on the gate voltage with a characteristic two-peak structure near the Dirac point. The origin of PHE is the peculiar time-reversal-breaking effect of an in-plane magnetic field, which anisotropically lifts the protection of surface Dirac fermions from backscattering. The observed PHE provides a useful tool to analyze and manipulate the topological protection of the TI surface

Persistence of Topological Order and Formation of Quantum Well States in Topological Insulators Bi2(Se,Te)3 under Ambient Conditions

The topological insulators represent a unique state of matter where the bulk is insulating with an energy gap while the surface is metallic with a Dirac cone protected by the time reversal symmetry. These characteristics provide a venue to explore novel quantum phenomena in fundamental physics and show potential applications in spintronics and quantum computing. One critical issue directly related with the applications as well as the fundamental studies is how the topological surface state will behave under ambient conditions (1 atmosphere air and room temperature). In this paper, we report high resolution angle-resolved photoemission measurements on the surface state of the prototypical topological insulators, Bi2Se3, Bi2Te3 and Bi2(Se0.4Te2.6), upon exposing to ambient conditions. We find that the topological order persists even when the surface is exposed to air at room temperature. However, the surface state is strongly modified after such an exposure. Particularly, we have observed the formation of two-dimensional quantum well states near the surface of the topological insulators after the exposure which depends sensitively on the original composition, x, in Bi2(Se3-xTex). These rich information are crucial in utilizing the surface state and in probing its physical properties under ambient conditions.Comment: 15 Pages, 4 Figure

Population dynamic of bony fishes in the southern part of the Caspian Sea

This study was conducted to determine growth parameters, catch and fishing effort trends, stock assessment and Acceptable Biological Catch (ABC) of bony fishes in the Iranian coastal waters of Caspian Sea in the years 2010-2011 and 2011-2012. According to the result, the numbers of beach seines were 131 and 128 and their fishing efforts were observed 50184 and 42255 beach seining during 2010-11 and 2011-12, respectively. The catch per unit of effort CPUE) was calculated 182.9 and 205.6 kg/haul during two sampling periods, respectively. The total catches (including illegal fishing) were also obtained 16601.5 mt and 17034.1 mt during 2010-11 and 2011-12, respectively. The highest proportion of catch was belonged to kutum and golden grey mullet (86% and 88%, respectively) in two fishing seasons aforementioned above. Growth parameters of kutum were estimated as K=0.21/yr, L_∞ = 60.0 cm, t-0 = 0/yr. The Growth parameters were K=0.18/yr, L_∞ = 61.1 cm, t-0 = -0.14/yr for golden gray mullet and were K=0.12/yr, L_∞ = 73.6 cm, t-0 = 0.92/yr for common carp. Based on catch-at-age data, in the years 2010-2011 and 2011-2012, the total biomass, from the biomass-based cohort analysis were estimated 41700mt and 34400 mt for kutum and 14600 mt and 14400 mt for golden grey mullet, respectively. The reference points of F0.1 and F35% were 0.41/yr and 0.34/yr for kutum and 0.36/yr and 0.33/yr for golden grey mullet, respectively. Stock enhancement plays an important role in recovery of kutum stocks in the Iranian coastal waters of Caspian Sea. There is a significantly negative correlation between fingerlings released and condition factor (CF) and recruitment and CF. The different trends for fingerlings, recruitments and CF suggest that CF may be partly density-dependent, declining at high population sizes due to intra-specific competition. Therefore, more research should be conducted to determine the desirable level of artificial propagation. Food consumed by fish species, Rutilus frisii kutum, Rutilus rutilus caspicus, Cyprinus carpio, Liza auratus and Liza saliens were included Foraminifera, Porifera, Annelida, Mollusca, Arthropoda, filamentous algae, fish eggs and detritus.The results showed that Rutilusfrisii kutum generally feed on Balanus and Cerastorderma. The main food item for Cyprinuscarpio, Liza auratus and Liza salienswas detritus. Based on available models, the ABCs were estimated as 6600-7400 mt for kutum and 2200-2800 mt for golden grey mullet (with precautionary approach 6600 mt and 2200 mt for kutum and mullet, respectively) in 2011-12. Two species (kutum and golden grey mullet) are vulnerable to environmental factors, and these factors should be considered in the stock assessment and management of the fish. For two species, the ABC with a lower andmore accurate value based onmore information, should be selectedfor the implementation of a precautionary management approach

Use of plant-based sorbents and mycodegradation for the elimination of endocrine disrupting chemicals from soil: A novel facile and low-cost method

Soil contamination is a worldwide emergency that requires prompt, economical and eco-compatible solutions. This work explored an innovative approach consisting of sequential adoption of plant-based adsorbents and mycodegradation to remediate a multi-contaminated soil. Wood biochar (BC) and hydrochar (HC) samples, and spent coffee grounds (CG) were used to remove from the soil two well-known endocrine disrupting chemicals (EDCs), 4-tert-octylphenol (OP) and bisphenol A (BPA), and two suspected EDCs, the fungicide boscalid and the herbicide metribuzin, each at a concentration of 1 mg L−1. The adsorbents were spread on a layer of tissue–non-tissue and overlaid to the soil. After 2, 4 and 7 d of exposure to the polluted soil, the adsorbents were removed. The percentages of OP, BPA, boscalid and metribuzin adsorbed in just 2 d onto BC were, respectively, 80, 62, 34 and 50%. whereas they were lower on HC and much lower on CG. At the two successive times, the amounts of EDCs removed increased, following the same trend OP > BPA > metribuzin > boscalid for all materials and all samplings. The materials removed from the soil after 7 d were inoculated with the fungi Trametes versicolor and Pleurotus eryngii, separately, and incubated for 7 and 14 days. After 7 d, the maximum degradation was observed for OP in any material, being averagely 70 and 74% by T. versicolor and P. eryngii, respectively. After 14 d, averagely, and with slight differences among treatments, P. eryngii degraded 83, 75, 68 and 63% of OP, BPA, boscalid and metribuzin, respectively, while T. versicolor was slightly less effective. Plant assays clearly showed a noticeable reduction of soil phytotoxicity after the remediation treatment with the adsorbents, especially BC. The overall results obtained encourage to study in deep this strategy that allows both the remediation of soil and the elimination of pollutants with a very facile and inexpensive procedure

Incommensurate structure of GdBaCo2O5+δ (δ∼0.38)

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