Using time-resolved multi-dimensional angle-resolved photoelectron spectroscopy (ARPES) we explore the angular momentum transfer of low energy polarized photons to two prototype topological insulators, Bi2Te2Se and Bi2Se3. Our comparative study is based on the analysis of circular dichroism in the photoemission yield of photoexcited Dirac states, and reveals that the spin vector of in-gap Dirac electrons in Bi2Te2Se presents a more pronounced out-of-plane component compared to that of Bi2Se3. We show that the multi-dimensional ARPES approach can be effectively used to observe the spin texture of photoexcited topological insulators, and to unambiguously disentangle experimental geometry and matrix element effects.

Surface electronic properties of Bi2Se3 and Bi2Se3 topological insulators are known to evolve with varying surface termination. In this work, the (111) surface of Bi2Se3 has been studied with a comprehensive combination of experimental and computational (density functional theory) methods. It has been demonstrated that with proper preparation conditions the system can be forced into a new stable surface termination - a sub-monolayer of bismuth acquired through selective Se desorption - which has not been explored yet.

We observed waveforms and images of THz radiation from Bi 2 Te 3 /Te striped structures with a laser terahertz emission microscope (LTEM). The results indicate that THz emission from Te is stronger than that from Bi 2 Te 3 and the amplitude of polarized THz wave in parallel to the striped lines is larger than that in perpendicular.

We observed waveforms and images of THz radiation from BizTe(3)/Te striped structures with a laser terahertz emission microscope (LTEM). The results indicate that THz emission from Te is stronger than that from Bi2Te3 and the amplitude of polarized THz wave in parallel to the striped lines is larger than that in perpendicular.

Hardness testing is an efficient means for monitoring the change in mechanical properties of irradiated materials. The evaluation of the indentation load-displacement data is commonly based on the Oliver-Pharr method, which estimates the projected contact area between the indenter tip and the material surface using Sneddon's elastic contact solution. This simplified method can lead to significant errors when the indented elastic-plastic material exhibits extensive pile-up around the indenter, which is typical for a material with a smaller strain-hardening exponent n and a smaller yield strength-to-elastic modulus ratio sigma(y)/E. Since both these mechanical properties are influenced by the neutron irradiation, one must be careful with the interpretation of measured indentation hardness. In this study, a finite element simulation was used to investigate the effect of pile-up on indentation hardness evaluation. Load-displacement curves, contact areas evaluated by both Oliver-Pharr method and finite element nodes in contact and the corresponding hardnesses were obtained for the 15Ch2MFA (15Cr2MoV) tempered bainitic steel in non-irradiated and neutron-irradiated state. The Oliver-Pharr method underestimates the true contact area, and therefore overestimates hardness by factor of 1.32 and 1.40 for non-and neutron-irradiated state, respectively. Despite this discrepancy, the Oliver-Pharr method as well as direct observation of the contact area are able to indicate the increase of hardness due to neutron-irradiation (15% vs. 8% increase in hardness).

Twin-roll cast aluminum strips based on EN AW3003 alloy with a small addition of Zr and Cr further processed by constrained groove pressing (CGP) were studied in this work. Vickers microhardness measurements were used to investigate an inhomogeneous distribution of microhardness as a result of an inhomogeneous strain distribution imposed by CGP. Results are consistent with the finite element method simulations of the total equivalent plastic strain which predicts higher accumulated strain in areas close to the edges of CGP dies. Microhardness saturates after two CGP cycles due to a dynamic recovery. Electron backscatter diffraction, light optical microscopy and transmission electron microscopy were used to study grain and dislocation structure and to compare domains with higher and lower microhardness. The sample after 3 CGP cycles exhibits an unusual mechanical behavior. Domains with higher microhardness exhibit a higher degree of recovery with a lower dislocation density than domains with lower microhardness.

Using femtosecond time-and angle-resolved photoemission spectroscopy, we explore the out-of-equilibrium dynamics of surface fermions in the topological system Bi2Te2Se. We show that the presence of localized states from defects at the surface is one of the key material parameters undergirding the long relaxation time of photoexcited Dirac electrons lying in the projected band gap of the bulk-insulating pristine compound. Doping this ternary compound with Sn substituting on Bi sites, while desirably increasing the resistivity at low temperatures decreases decay times of the excited homologous Dirac electrons. On the basis of these observations, we argue that long relaxation times can be ultimately controlled by a charge transfer to the surface.

Despite intensive investigations of Bi2Se3 in past few years, the size and nature of the bulk energy band gap of this well-known 3D topological insulator still remain unclear. Here we report on a combined magneto-transport, photoluminescence and infrared transmission study of Bi2Se3, which unambiguously shows that the energy band gap of this material is direct and reaches E g = (220 ± 5) meV at low temperatures.

Despite intensive investigations of Bi 2 Se 3 in past few years, the size and nature of the bulk energy band gap of this well-known 3D topological insulator still remain unclear. Here we report on a combined magneto-transport, photoluminescence and infrared transmission study of Bi 2 Se 3 , which unambiguously shows that the energy band gap of this material is direct and reaches E g = (220 ± 5) meV at low temperatures.

Bismuth selenide – the prominent topological insulator – has been recently reported as a material exhibiting an extraordinary strong Faraday rotation. This effect has been identified as due to interband excitations in bulk promoting electrons from the valence to the conduction band, in which the electron gas is partially spin-polarized due to the Zeeman effect. In this work, we test the Faraday rotation in Bi2 Se3 in high magnetic fields, when the conduction band electrons reach their full spin polarization. We find that the Faraday angle becomes in this regime almost independent of the applied magnetic field. This contrasts with the Faraday effect observed in this system at low magnetic fields, where the Faraday angle scales linearly with B and may thus be described by a conventional Verdet law.

The Faraday effect is a representative magneto-optical phenomenon, resulting from the transfer of angular momentum between interacting light and matter in which time-reversal symmetry has been broken by an externally applied magnetic field. Here we report on the Faraday rotation induced in the prominent 3D topological insulator Bi 2 Se 3 due to bulk interband excitations. The origin of this non-resonant effect, extraordinarily strong among other non-magnetic materials, is traced back to the specific Dirac-type Hamiltonian for Bi 2 Se 3 , which implies that electrons and holes in this material closely resemble relativistic particles with a non-zero rest mass.

Bulk-related conduction electron spin resonance and conduction hole spin resonance were investigated in Bi2Se3, a three-dimensional topological insulator. Electrons in the conduction band and holes in the valence band both have spin 1/2. The effective g-factors for conduction electrons are equal to 27.3 +/- 0.15 for magnetic field parallel to the c axis and 19.48 +/- 0.07 for magnetic field perpendicular to the c axis, whereas for conduction holes 29.90 +/- 0.09 for magnetic field parallel and 18.96 +/- 0.04 for magnetic field perpendicular to the c axis, respectively. Nonparabolicity effects were not observed in the investigated low carrier concentration range, below 8 x 10(17) cm(-3). Large g-factors, higher by an order of magnitude than the free electron value, are due to strong spin-orbit interactions in Bi2Se3. The striking similarity of the spin resonances due to conduction electrons and holes confirms the peculiar symmetry between the conduction and valence bands of Bi2Se3, both having similar effective masses and spin character.

The aim of this work was to obtain PbTe material in the desired way in order to control the combined impact of lattice disorder, nanoscale precipitates and reduced grain sizes on the thermoelectric properties of this material. To achieve this, PbTe ingot doped with Ag was obtained by the Bridgman method, followed by ball-milling, cold pressing and sintering. In order to estimate crystallites diameters grain size measurements were carried out using the optical microscopy. Studies of electrical and thermoelectric properties of fine-grained material were performed. In order to analyze the morphology and the composition scanning electron microscopy and energy-dispersive X-ray spectroscopy were performed. Energy-dispersive X-ray spectroscopy analysis also revealed presence of Ag-Te precipitates.

The elastic finite element computations of the indentation process with the Berkovich indenter are performed to examine the effect of cubic crystal and indenter orientation on indentation moduli of anisotropic material. Three metals with a cubic crystal lattice and various degree of elastic anisotropy from 1 to 9 are studied: tungsten, AISI 304 steel and beta-brass. Differences in anisotropy ratios expressed by the Young moduli on the one side and by the indentation moduli on the other side are quantified.

L. Ohnoutek, M. Hakl, M. Veis, B. A. Piot, C. Faugeras, G. Martinez, M. V. Yakushev, 4 R. W. Martin, Č. Drašar, A. Materna, G. Strzelecka, A. Hruban, M. Potemski, and M. Orlita 1, ∗ Institute of Physics, Charles University, Ke Karlovu 5, CZ-121 16 Praha 2, Czech Republic Laboratoire National des Champs Magnétiques Intenses, CNRS-UJF-UPS-INSA, 25, avenue des Martyrs, 38042 Grenoble, France Department of Physics, SUPA, Strathclyde University, G4 0NG Glasgow, UK Ural Federal University and Institute of Solid State Chemistry of RAS, Ekaterinburg, 620002, Russia Institute of Applied Physics and Mathematics, Faculty of Chemical Technology, University of Pardubice, Studentská 84, 532 10 Pardubice, Czech Republic Institute of Electronic Materials Technology, ul. Wolczynska 133, PL 01-919 Warsaw, Poland (Dated: December 4, 2015)

Nuclear magnetic resonance (NMR) and transport measurements have been performed at high magnetic fields and low temperatures in a series of n-type Bi2Se3 crystals. In low-density samples, a complete spin polarization of the electronic system is achieved, as observed from the saturation of the isotropic component of the Bi-209 NMR shift above a certain magnetic field. The corresponding spin splitting, defined in the phenomenological approach of a 3D electron gas with a large (spin-orbit-induced) effective g factor, scales as expected with the Fermi energy independently determined by simultaneous transport measurements. Both the effective electronic g factor and the "contact" hyperfine coupling constant are precisely determined. The magnitude of this latter reveals a nonnegligible s character of the electronic wave function at the bottom of the conduction band. Our results show that the bulk electronic spin polarization can be directly probed via NMR and pave the way for future NMR investigations of the electronic states in Bi-based topological insulators.

This paper provides a useful guide how to characterize material anisotropy by nanoindentation. Hardness and indentation modulus of austenitic stainless steel (grade A304) were characterized by instrumented indentation at the grain scale (at low indentation load and depth of penetration). We applied the grid indentation method on an area containing several grains with different crystallographic orientation which was simultaneously characterized by electron back-scatter diffraction. Hardness and indentation modulus dependencies on crystallographic orientation were then evaluated and compared with single crystal Young’s modulus and finite element simulations.