Transport and thermoelectric properties of the LaAlO3_3/SrTiO3_3 interface

The transport and thermoelectric properties of the interface between SrTiO$_3$ and a 26-monolayer thick LaAlO$_3$-layer grown at high oxygen-pressure have been investigated at temperatures from 4.2 K to 100 K and in magnetic fields up to 18 T. For $T>$ 4.2 K, two different electron-like charge carriers originating from two electron channels which contribute to transport are observed. We probe the contributions of a degenerate and a non-degenerate band to the thermoelectric power and develop a consistent model to describe the temperature dependence of the thermoelectric tensor. Anomalies in the data point to an additional magnetic field dependent scattering.Comment: 7 pages, 4 figure

Probing the surface states in Bi2Se3 using the Shubnikov-de Haas effect

Shubnikov-de Haas (SdH) oscillations are observed in Bi2Se3 flakes with high carrier concentration and low bulk mobility. These oscillations probe the protected surface states and enable us to extract their carrier concentration, effective mass and Dingle temperature. The Fermi momentum obtained is in agreement with angle resolved photoemission spectroscopy (ARPES) measurements performed on crystals from the same batch. We study the behavior of the Berry phase as a function of magnetic field. The standard theoretical considerations fail to explain the observed behavior.Comment: 6 pages, 8 figures. Accepted to Physical Review

Stress Inducible Overexpression of AtHDG11 Leads to Improved Drought and Salt Stress Tolerance in Peanut (Arachis hypogaea L.)

Peanut is an important oilseed and food legume cultivated as a rain-fed crop in semi-arid tropics. Drought and high salinity are the major abiotic stresses limiting the peanut productivity in this region. Development of drought and salt tolerant peanut varieties with improved yield potential using biotechnological approach is highly desirable to improve the peanut productivity in marginal geographies. As abiotic stress tolerance and yield represent complex traits, engineering of regulatory genes to produce abiotic stress-resilient transgenic crops appears to be a viable approach. In the present study, we developed transgenic peanut plants expressing an Arabidopsis homeodomain-leucine zipper transcription factor (AtHDG11) under stress inducible rd29A promoter. A stress-inducible expression of AtHDG11 in three independent homozygous transgenic peanut lines resulted in improved drought and salt tolerance through up-regulation of known stress responsive genes (LEA, HSP70, Cu/Zn SOD, APX, P5CS, NCED1, RRS5, ERF1, NAC4, MIPS, Aquaporin, TIP, ELIP) in the stress gene network, antioxidative enzymes, free proline along with improved water use efficiency traits such as longer root system, reduced stomatal density, higher chlorophyll content, increased specific leaf area, improved photosynthetic rates, and increased intrinsic instantaneous WUE. Transgenic peanut plants displayed high yield compared to non-transgenic plants under both drought and salt stress conditions. Holistically, our study demonstrates the potentiality of stress-induced expression of AtHDG11 to improve the drought, salt tolerance in peanut

Josephson supercurrent through a topological insulator surface state

Topological insulators are characterized by an insulating bulk with a finite band gap and conducting edge or surface states, where charge carriers are protected against backscattering. These states give rise to the quantum spin Hall effect without an external magnetic field, where electrons with opposite spins have opposite momentum at a given edge. The surface energy spectrum of a threedimensional topological insulator is made up by an odd number of Dirac cones with the spin locked to the momentum. The long-sought yet elusive Majorana fermion is predicted to arise from a combination of a superconductor and a topological insulator. An essential step in the hunt for this emergent particle is the unequivocal observation of supercurrent in a topological phase. Here, we present the first measurement of a Josephson supercurrent through a topological insulator. Direct evidence for Josephson supercurrents in superconductor (Nb) - topological insulator (Bi2Te3) - superconductor e-beam fabricated junctions is provided by the observation of clear Shapiro steps under microwave irradiation, and a Fraunhofer-type dependence of the critical current on magnetic field. The dependence of the critical current on temperature and length shows that the junctions are in the ballistic limit. Shubnikov-de Haas oscillations in magnetic fields up to 30 T reveal a topologically non-trivial two-dimensional surface state. We argue that the ballistic Josephson current is hosted by this surface state despite the fact that the normal state transport is dominated by diffusive bulk conductivity. The lateral Nb-Bi2Te3-Nb junctions hence provide prospects for the realization of devices supporting Majorana fermions

Mechanical properties of equal channel angular extruded magnesium boride (MgB2) powder in tubes (PITs)

The MgB2 PITs, prepared by filling Fe tubes with MgB2 as a core, were processed through different number of passes at room temperature via Routes A, B-A, C and BC. The mechanical properties of the PITs were measured in terms of density and hardness. The extent of the compaction was also studied through shear punch test. The shape of the compacts remains circular even after four passes via Route C & B-C. Higher density and hardness along with higher USS is observed from the PITs of Route C compared to Route BC. The PITs processed through Route A and Route BA did not show sufficient compaction to carryout the density measurements. Thus, the current study shows that Route C is the optimal route; to attain good mechanical proper-ties in ECAE processed MgB2 PITs with Fe tube

Multipass equal channel angular extrusion of MgB2 powder in tubes

In the current study multipass equal channel angular extrusion (ECAE) is adopted for the first time to study the applicability of the process to compact magnesium boride (MgB2) Powder in tubes (PITs). The influence of number of ECAE passes on MgB2 PITs was also analyzed in terms of microstructure, density and mechanical properties. MgB2 PITs with iron tube were processed up to six ECAE passes. X-ray analysis of the compacts showed no other phases, other than MgO, in MgB2 compacts even after large mechanical working and annealing. Simple shear stresses predominant in ECAE constantly rendered compaction of the hard brittle MgB2 powders. (c) 2007 Elsevier B.V. All rights reserved

MnCo2O4 nanosphere synthesis for electrochemical applications

The present work addresses the important need of new materials to improve energy storage materials. The synthesis of MnCo2O4 nanospheres by employing solvothermal method at different incubation times was carried out. The effects of reaction time on structural, morphological, and electrochemical studies were briefly investigated. The X-ray diffraction result unveils the formation of cubic-structured MnCo2O4 nanospheres with Fd3m (2 2 7) space group. The appearance of two Raman peaks at 480 and 662 cm−1 was greatly attributed to the stretching vibration mode of M–O (M = Mn, Co), and substantiates the formation of MnCo2O4. The presence of functional group and characteristics group was analyzed by Fourier-transform infrared spectroscopy. The scanning electron microscope image clearly indicated different sizes of nanoparticles due to the effect of solvothermal reaction period. The energy storage behavior of MnCo2O4 nanospheres was studied by employing the cyclic voltammetric and charge–discharge cycles. The results confirmed the pseudocapacitive nature of MnCo2O4 nanoparticles (RF3) with porous, spherical nanostructure with larger radius than others and contribute to better specific capacitance of 252 F g−1 at current density of 1 A g−1 which could be considered as a potential candidate for pseudocapacitive electrode for energy storage devices. Keywords: Cubic, MnCo2O4, Nanospheres, PVP, Fd3m (2 2 7) space group, Energy storag