M. B. Babanly

Atom-specific spin mapping and buried topological states in a homologous series of topological insulators

A topological insulator is a state of quantum matter that, while being an insulator in the bulk, hosts topologically protected electronic states at the surface. These states open the opportunity to realize a number of new applications in spintronics and quantum computing. To take advantage of their peculiar properties, topological insulators should be tuned in such a way that ideal and isolated Dirac cones are located within the topological transport regime without any scattering channels. Here we report ab-initio calculations, spin-resolved photoemission and scanning tunnelling microscopy experiments that demonstrate that the conducting states can effectively tuned within the concept of a homologous series that is formed by the binary chalcogenides (Bi(2)Te(3), Bi(2)Se(3) and Sb(2)Te(3)), with the addition of a third element of the group IV.

Disentanglement of Surface and Bulk Rashba Spin Splittings in Noncentrosymmetric BiTeI

BiTeI has a layered and non-centrosymmetric structure where strong spin-orbit interaction leads to a giant spin splitting in the bulk bands. Here we present high-resolution angle-resolved photoemission (ARPES) data in the UV and soft x-ray regime that clearly disentangle the surface from the bulk electronic structure. Spin-resolved UV-ARPES measurements on opposite, nonequivalent surfaces show identical spin structures, thus clarifying the surface state character. Soft x-ray ARPES data clearly reveal the spindle-torus shape of the bulk Fermi surface, induced by the spin-orbit interaction. PACS numbers: 71.20.Nr, 71.70.Ej, 79.60.Bm 1 ar X iv :1 20 4. 21 96 v1 [ co nd -m at .m tr lsc i] 1 0 A pr 2 01 2 The breaking of inversion symmetry and its influence on the spin structure of surface states under action of spin–orbit interaction (SOI) has been extensively studied in recent years [1, 2]. The main finding is that the surface states become spin-split according to the Rashba model [3] resulting in two spin-polarized concentric Fermi contours. The lack of inversion symmetry in the bulk crystal structure is expected to induce a spin splitting with a more complex bandand spin-structure. Combined with strong SOI the Fermi surface can take the shape of a torus [4]. For non-centrosymmetric superconductors such as for example CePt3Si [5] this peculiar band structure is expected to result in topologically protected spin polarized edge states reminiscent of Majorana modes [6]. Recently, an ARPES and spin-resolved ARPES study by Ishizaka et al. [7] proposed that the semiconductor BiTeI features a very large spin-splitting, arising from the broken inversion symmetry in the crystal bulk and a strong SOI. Theoretical work based on the perturbative k ·p formalism linked the unusually large spin splitting in BiTeI to the negative crystal field splitting of the top valence bands [8]. Optical transition measurements [9] are in accordance with the giant bulk spin-splitting of the gap defining valence and conduction bands predicted by first principle calculations [7, 8]. In addition it was shown in recent theoretical work that BiTeI can become a topological insulator under action of hydrostatic pressure [10], and thus is closely related to non-centrosymmetric topological superconductors. The present study provides first band mapping of a system without bulk inversion symmetry and giant SOI by the example of BiTeI, featuring a three-dimensional Rashba splitting of the bulk bands. Further it is shown that the Rashba-split state observed for this material in the UV photon energy regime is not a quantum well state [7] but rather a surface state, using a simple symmetry argument based on spin-resolved ARPES (SARPES) measurements, which is confirmed by first principle calculations. All measurements were performed at the Swiss Light Source of the Paul-Scherrer-Institut. The SARPES data was measured with the Mott polarimeter at the COPHEE endstation [11] of the Surface and Interface Spectroscopy beamline at a photon energy of 24 eV. The spin-integrated data at photon energies 20-63 eV were taken at the high-resolution ARPES endstation at the same beamline. The soft x-ray ARPES data were taken at the SX-ARPES endstation of the ADRESS beamline at photon energies of 310-850 eV. All spin-integrated measurements were performed at a sample temperature of 11 K and a base pressure lower than 10−10 mbar, the SARPES data was taken at 20 K.

Observation of a highly spin-polarized topological surface state in GeBi2Te4

, the newly discovered three-dimensional topological insulator, has been studied by means of the state of the art spin- andangle-resolved photoemission spectroscopy. It has been revealed that the disorder in the crystal hasa minor effect on the surface state spin polarization and it exceeds 75% near the Dirac point in thebulk energy gap region (∼180 meV). This new finding for GeBi

The EMF Method with Solid-State Electrolyte in the Thermodynamic Investigation of Ternary Copper and Silver Chalcogenides

Design and optimization of technology of creating new multicomponent inorganic materials, in particular, chalcogenides of metals are perspective functional materials in modern electronic techniques, are based on results of thermodynamic calculations. In turn, to ensure high accuracy of similar calculations is needs reliable dates on fundamental thermodynamic characteristics of corresponding phases. However, the analysis of literature data shows that unlike binary system, the thermodynamic properties of ternary and multicomponent systems are studied quite insufficiently. In our opinion, elimination of this blank wide application of electromotive forces method (EMF) one of the most exact experimental methods of chemical thermodynamics appreciably can promote. This method is applied with the big success to the thermodynamic studying of liquid binary and ternary metal systems, which more than 70 % of the available information is concerning to EMF method. Wide application of EMF method for studying of liquid metal systems is caused not only that the specified systems are the most suitable objects of investigation by this method, but also that the mathematical apparatus of chemical thermodynamics allows to calculate strictly integrated thermodynamic functions (ITF) homogeneous binary and ternary system on the basis of values partial thermodynamic functions (PTF) one of components in wide compositions area [M.Babanly et.al, 1992; Morachevskii et.al., 2003; Wagner, 1952]. Unfortunately, specific features and conditions of application EMF method to the heterogeneous systems have not been considered in long time. In the 80th years of last century we have undertaken attempts of elimination of this blank and have developed conditions of application EMF method to heterogeneous metal and semi-conductor systems [M.Babanly, 1985, 1992]. In this chapter we offer the rational method of calculation integral thermodynamic functions of intermediate phases in the ternary heterogeneous systems from PTF of one of components by using of the phase diagram and thermodynamic functions of some boundary binary phases and elementary components. The EMF method with liquid electrolyte has been realized on an example over 30 systems of Thallium-Metal-Chalcogen and have been obtained complexes interconsistency thermodynamic data for the many ternary chalcogenides of thallium [M.Babanly et.al, 1992].

Thermodynamic study of the Ag-As-Se and Ag-S-I systems using the EMF method with a solid Ag4RbI5 electrolyte

The EMF method with a solid Ag4RbI5 superionic conductor was used to study the Ag-As-Se and Ag-S-I systems in the composition ranges of Ag2Se-As2Se3-Se and Ag2S-AgI-S, accordingly. Their solid-phase equilibrium diagrams are constructed or specified. The existence of ternary AgAs3Se5, AgAsSe2, Ag3AsSe3, Ag7AsSe6, Ag3SI compounds is confirmed. The standard partial and integral thermodynamic formation functions and also standard entropies were calculated for these compounds for the first time.

New thallium neodymium tellurides

The phase equilibria in the composition region Tl2Te-Tl2Te3-Nd2Te3-NdTe of the Tl-Nd-Te system have been studied by differential thermal analysis and x-ray diffraction, and the 500-K section of its phase diagram has been mapped out. The ternary compounds identified are Tl9NdTe6, Tl4NdTe3, Tl6Nd4Te9, Tl4Nd6Te11, Tl2NdTe3, TlNdTe3, and TlNd3Te6. X-ray powder diffraction data indicate that the compounds Tl9NdTe6 and Tl4NdTe3 are structural analogs of Tl5Te3 and have tetragonal cell parameters a = 8.855 Å, c = 13.010 Å and a = 8.858 Å, c = 12.998 Å, respectively (sp. gr. I4/mcm, Z = 4). Tl9NdTe6 and Tl4NdTe3 are phases of variable composition (δ-phase), and their fields cover most of the Tl2Te-Tl5Te3-Tl4NdTe3 composition triangle. The structure of Tl5Te3 and its ternary analogs is discussed, and the conclusion is drawn that, in spite of the broad field of the δ-phase, Tl9NdTe6 and Tl4NdTe3 are daltonides, i.e., distinct chemical compounds.

Manipulating the Topological Interface by Molecular Adsorbates: Adsorption of Co-Phthalocyanine on Bi2Se3.

Topological insulators are a promising class of materials for applications in the field of spintronics. New perspectives in this field can arise from interfacing metal-organic molecules with the topological insulator spin-momentum locked surface states, which can be perturbed enhancing or suppressing spintronics-relevant properties such as spin coherence. Here we show results from an angle-resolved photemission spectroscopy (ARPES) and scanning tunnelling microscopy (STM) study of the prototypical cobalt phthalocyanine (CoPc)/Bi2Se3 interface. We demonstrate that that the hybrid interface can act on the topological protection of the surface and bury the Dirac cone below the first quintuple layer.

Multiple coexisting Dirac surface states in three-dimensional topological insulator PbBi6Te10

By means of angle-resolved photoemission spectroscopy (ARPES) measurements, we unveil the electronic band structure of three-dimensional PbBi6Te10 topological insulator. ARPES investigations evidence multiple coexisting Dirac surface states at the zone-center of the reciprocal space, displaying distinct electronic band dispersion, different constant energy contours, and Dirac point energies. We also provide evidence of Rashba-like split states close to the Fermi level, and deeper M- and V-shaped bands coexisting with the topological surface states. The experimental findings are in agreement with scanning tunneling microscopy measurements revealing different surface terminations according to the crystal structure of PbBi6Te10. Our experimental results are supported by density functional theory calculations predicting multiple topological surface states according to different surface cleavage planes.

Phase diagram of the Sb–Te–I system and thermodynamic properties of SbTeI

Abstract The Sb–Te–I system was investigated by using differential thermal analysis, X-ray diffraction analysis and electromotive force measurements with an antimony electrode. A number of polythermal sections and the projection of the liquidus surface were constructed. The fields of the primary crystallization, as well as the types and coordinates of nonand monovariant equilibriums were determined. It is shown that the quasi-binary sections SbI3–Sb2Te3, SbI3–Te, and SbI3–TeI4 triangulate the Sb–Te–I system, leading to four independent subsystems. From the electromotive force measurements, the partial molar functions of antimony as well as the standard integral thermodynamic functions of SbTeI were calculated. The latter were found to have the following values: ΔG0f,298 = −55.77 ± 1.7 kJ · mol−1; ΔH0f,298 = −55.72 ± 1.39 kJ · mol−1; S0298 = 153.5 ± 2.8 J · K−1 · mol−1.

A thermodynamic study of Cu—Tl—S system by EMF method with Cu4RbCl3I2 solid electrolyte

AbstractThe Cu—Tl—S system was studied by the EMF method with Cu4RbCl3I2 solid Cu+-conducting electrolyte within the temperature range from 300 to 390 K. The earlier plotted solid-phase equilibrium diagram of this system was confirmed, the partial copper molar functions