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A comparative study of the properties of topological insulator Bi2Te2Se (BTS) crystals grown by the vertical Bridgeman method is described. Two defect mechanisms that create acceptor impurities to compensate for the native n-type carriers are compared: Bi excess, and light Sn doping. Both methods yield low carrier concentrations and an n-p crossover over the length of the grown crystal boules, but lower carrier concentrations and higher resistivities are obtained for the Sn-doped crystals, which reach carrier concentrations as low as 8×1014 cm-3. Further, the temperature dependent resistivities for the Sn-doped crystals display strongly activated behavior at high temperatures, with a characteristic energy of half the bulk band gap. The (001) cleaved Sn-doped BTS crystals display high quality Shubnikov de Haas (SdH) quantum oscillations due to the topological surface state electrons. Angle resolved photoelectron spectroscopy (ARPES) characterization shows that the Fermi energy (EF) for the Sn-doped crystals falls cleanly in the surface states with no interference from the bulk bands, which the Dirac point for the surface states lies approximately 60meV below the top of the bulk valence band maximum, and allows for a determination of the bulk and surface state carrier concentrations as a function of Energy near EF. Electronic structure calculations that compare Bi excess and Sn dopants in BTS demonstrate that Sn acts as a special impurity, with a localized impurity band that acts as a charge buffer occurring inside the bulk band gap. We propose that the special resonant level character of Sn in BTS gives rise to the exceptionally low carrier concentrations and activated resistivities observed. [ABSTRACT FROM AUTHOR]

Since their prediction and subsequent discovery, topological semimetals (TSMs) have established a new research area, which includes the prediction of new semimetal phases, the realization of new materials types, and the exploration of their properties as well as potential for incorporation into devices. In their contribution, Xu I et al. i predicted that the noncentrosymmetric superconductor YCoC SB 2 sb (reported Tc = 4.2 K) is a TSM in its normal state.[42] The authors show based on first principles calculations that YCoC SB 2 sb should host multiple Weyl nodes as well as Fermi arcs on its surface. In this collection, Muechler I et al. i showed with first principles calculations that this 7 K superconductor is a nodal line semimetal.[43] NaAlSi crystallizes in the same crystal structure as the nodal line semimetal ZrSiS,[[44]] but here, the band inversion stems from different orbitals. In this light, Negishi I et al. i studied thin films of the Perovskite-type iridates SrIrO SB 3 sb and CaIrO SB 3 sb , which are known to be Dirac line node semimetals.[52] The authors substitute Sn on the Ir position and found that while in the Strontium iridate, this causes a transition from a semimetallic state to a weakly ferromagnetic insulating state, no clear signature of such a transition is seen in the calcium iridate. [Extracted from the article]

We report the synthesis of MgB[sub 2] with bulk superconducting properties by conventional solid state methods at temperatures as low as 550 °C. Mg deficiencies of the type Mg[sub 1-x]B[sub 2] were tested. T[sub c] was found to decrease by about 1 K at large x, though the amount of nonstoichiometry, if any, is likely to be very small. For specific processing conditions, indications of the 25–30 K transition often seen in thin films were seen in the bulk materials. The lower temperature transition may be associated with the grain boundaries. These results indicate that it should be possible to fabricate MgB[sub 2] with bulk properties in in situ thin films at temperatures of 600 °C or less. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Examines thermoelectric properties of semiconductor materials. Room-temperature Seebeck coefficient; Thermal conductivity; Sensitivity of transport properties to chemical doping and nonstoichiometry.

Presents a study which measured the real and imaginary parts of the dielectric function of racemic and chiral CE8. Alignment of the molecules in the samarium carbide phase; Determination of the change in the density of states at low frequencies; Values of the direct current electrical conductivities.

Presents a study which examined copper oxide superconductors using nuclear magnetic resonance and nuclear quadrupole resonance. Experimental procedures; Results of spin-lattice relaxation; Conclusion.

Neutron time-of-flight spectroscopy has been employed to study the crystal-field interaction in the pyrochlore titanate Ho[sub 2]Ti[sub 2]O[sub 7]. The crystal-field parameters and corresponding energy-level scheme have been determined from a profile fit to the observed neutron spectra. The ground state is a well separated E[sub g] doublet with a strong Ising-like anisotropy, which can give rise to frustration in the pyrochlore lattice. Using the crystal-field parameters determined for the Ho compound as an estimate of the crystal-field potential in other pyrochlore magnets, we also find the Ising type behavior for Dy. In contrast, the almost planar anisotropy found for Er and Yb prevents frustration, because of the continuous range of possible spin orientations in this case. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Discusses a study which investigated the dielectric properties of polycrystalline ceramics of (Ta[sub2]O[sub5])[sub1-x](SiO[sub2])[subx]. Background on the materials; Methods used; Results.

Reports on the measurement of the temperature dependent dielectric constants in the vicinity of room temperature for bulk ceramics. List of starting materials for ceramic synthesis; Information on the investigations of the Pb-Nb-Mg-Ti-O phase diagram; Summary of dielectric data for pyrochlore based oxides Pb-Nb-Mg-Ti-O.

Presents a study that examined epitaxial thin films of copper-oxide-based isotropic metallic oxide and superconducting heterostructures. Analysis of the crystalline properties and interfaces of the samples; Factors to consider when using copper-oxide-based isotropic metallic oxide materials as a normal-metal barrier; Investigation of the texture of the thin films.

Studies the structure and magnetic properties of epitaxial ferrite multilayer films. Determination of crystal orientation and rocking curve widths; Structural characterization of buffer films; Grain sizes of ferrite films grown on top of buffered substrates.

Local modes caused by defects play a significant role in the thermal transport properties of thermoelectrics. Of particular interest are charge-neutral defects that suppress thermal conductivity, without significantly reducing electrical transport. Here, we report a temperature dependent Raman study that identifies such a mode in a standard thermoelectric material, Bi2Te2Se. One of the modes observed, whose origin has been debated for decades, was shown most likely to be an antisite defect induced local mode. The anomalous temperature independent broadening of the local mode is ascribed to the random arrangement of Se atoms. The temperature renormalization of all modes is well explained by an anharmonic model-Klemens's model. [ABSTRACT FROM AUTHOR]

High quality hexagon plate-like Na3Bi crystals with large (001) plane surfaces were grown from a molten Na flux. The freshly cleaved crystals were analyzed by low temperature scanning tunneling microscopy and angle-resolved photoemission spectroscopy, allowing for the characterization of the three-dimensional (3D) Dirac semimetal (TDS) behavior and the observation of the topological surface states. Landau levels were observed, and the energy-momentum relations exhibited a linear dispersion relationship, characteristic of the 3D TDS nature of Na3Bi. In transport measurements on Na3Bi crystals, the linear magnetoresistance and Shubnikov-de Haas quantum oscillations are observed for the first time. [ABSTRACT FROM AUTHOR]

We demonstrate the van der Waals epitaxy of the topological insulator compound Bi2Te3 on the ferromagnetic insulator Cr2Ge2Te6. The layers are oriented with (001)Bi2Te3}||(001)Cr2Ge2Te6 and (110)Bi2Te3||(100)Cr2Ge2Te6. Cross-sectional transmission electron microscopy indicates the formation of a sharp interface. At low temperatures, bilayers consisting of Bi2Te3 on Cr2Ge2Te6 exhibit a large anomalous Hall effect (AHE). Tilted field studies of the AHE indicate that the easy axis lies along the c-axis of the heterostructure, consistent with magnetization measurements in bulk Cr2Ge2Te6. The 61K Curie temperature of Cr2Ge2Te6 and the use of near-stoichiometric materials may lead to the development of spintronic devices based on the AHE. [ABSTRACT FROM AUTHOR]

Cr2Ge2Te6 is proposed as an insulating ferromagnetic substrate for the growth of tetradymite-type topological insulators, based on a refined characterization of its transport, magnetic, optical, and calculated electronic properties. It is found to be a soft ferromagnet with no visible magnetic domains over relatively large length scales and to be highly insulating with an indirect band gap and low carrier concentration. Further we present the fabrication of Bi2Te3-Cr2Ge2Te6 heterostructure samples by chemical vapor deposition and show that crystals of the two phases are oriented such that the hexagonal Te planes are aligned at their interfaces. [ABSTRACT FROM AUTHOR]

Measurement of the low temperature specific heat of LaCoO3 single crystals reveals a previously unobserved Schottky anomaly with an energy level splitting, 0.5 meV, that is associated with the first excited spin state of the Co3+ ion. These states persist well below 2 K and have a g-factor around 3.5, consistent with the high-spin spin-orbit triplet, implying the existence of a low density (approximately 0.1% of the sites) of finite-spin Co ions even in the T=0 limit. We propose that these states are trapped at defects and are consistent with the magnetic excitons observed in earlier work. [ABSTRACT FROM AUTHOR]

We report the fabrication of field-effect transistors on single crystals of the highly anisotropic organic semiconductor tetramethyltetraselenafulvalene. We find maximum mobilities of 0.2 cm[sup 2]/V s at room temperature. We observe an exponential decrease of mobility with decreasing temperature with an activation energy 160±30 meV, independent of sample quality or fabrication method. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The reactivity of MgB[sub 2] with powdered forms of common substrate and electronic materials is reported. Reaction temperatures between 600 and 800 °C, encompassing the range commonly employed in thin-film fabrication, were studied. The materials tested for reactivity were ZrO[sub 2], yttria stabilized zirconia, MgO, Al[sub 2]O[sub 3], SiO[sub 2], SrTiO[sub 3], TiN, TaN, AlN, Si, and SiC. At 600 °C, MgB[sub 2] reacted only with SiO[sub 2] and Si. At 800 °C, however, reactions were observed for MgB[sub 2] with Al[sub 2]O[sub 3], SiO[sub 2], Si, SiC, and SrTiO[sub 3]. The T[sub c] of MgB[sub 2] decreased in the reactions with SiC and Al[sub 2]O[sub 3]. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Here we describe the results of an atomic resolution study of the structure and composition of both the interior of the grains, and the grain boundaries in polycrystalline MgB[sub 2]. We find that there is no oxygen within the bulk of the grains but significant oxygen enrichment at the grain boundaries. The majority of grain boundaries contain BO[sub x] phases smaller than the coherence length, while others contain larger areas of MgO sandwiched between BO[sub x] layers. Such results naturally explain the differences in connectivity between the grains observed by other techniques. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The Mössbauer effect of the 37.2 keV γ transition of 121Sb has been employed to study the electronic configuration of Sb ions in BaPb1-xSbxO3 superconducting materials. The isomer shift is constant as a function of Sb content and falls in the region correspoding to the Sb(V) valence state. The isomer shift of 7 mm/s is the lowest value yet observed for an Sb(V)O6 chromophore and indicates a high degree of covalency, corresponding to significant 5sm 5pn hybridization. The mixed valence state of an equal amount of Sb(III) and Sb(V) has not been observed. [ABSTRACT FROM AUTHOR]

Presents an abstract of the study 'Synthesis and Physical Properties of RNi[sub2]B[sub2]C and Related Materials,' by R.J. Cava.

Presents an abstract of the study 'Easy-Axis Transition in SmMn[sub2]Ge[sub2],' by R.B. van Dover, E.M. Gyorgy et al., published in the 'Journal of Applied Physics.'

Presents an abstract of a study on magnetoresistance in layered magnetic compounds. Factors that consist the structural phase transition that accompanies the magnetic transition; Function of arc-grown single crystals.