Q-dependent light scattering by electrons in LaB6

The inelastic light scattering by intraband electronic excitations in metallic lanthanum hexaboride has been studied in the temperature range of 10-300 K. General agreement has been obtained between the measured spectra and the spectra calculated within the band theory taking into account the renormalization of electron energies owing to electron-phonon scattering. The electron-phonon coupling constant λ and electron relaxation frequency Γ have been estimated. The dependence of the electron self-energies on the direction and magnitude of the wave vector has been revealed, implying the anisotropic electron-phonon interaction or the contribution from other electron scattering mechanisms. © 2013 Pleiades Publishing, Ltd

Raman evidence for nonadiabatic effects in optical phonon self-energies of transition metals

We report a Raman study of the effect of temperature on the self-energies of optical phonons in a number of transition metals with hexagonal-close-packed structure. Anisotropic softening of phonon energies and narrowing of phonon linewidths with increasing temperature are observed. These effects are reproduced in the calculations of phonon spectral functions based on ab initio electronic structures and with carrier scattering by phonons taken into account. The combined observations and results of simulations indicate a relation between observed anomalies and the renormalization of the electron spectrum due to electron-phonon interaction. It is emphasized that the temperature dependence of the phonon energies resembles anharmonic behavior but is actually an electron-induced effect. © 2016 American Physical Society

Multipeak quasielastic light scattering and high-frequency electronic excitations in honeycomb Li2RuO3

We measured the temperature dependence of low-frequency Raman spectra in Li2RuO3 and observed multipeak quasielastic scattering in the Ru honeycomb polarizations below and above the magnetostructural transition temperature. We attribute this scattering to the fluctuations of the energy density in the spin system. High-frequency electronic light scattering was observed at 2150cm-1. Its intensity increased significantly below the transition temperature, confirming substantial modification of the electronic structure due to removal of degeneracy in the t2g manifold of Ru4+ ions. © 2020 American Physical Society.This research was carried out within the state assignment of the Ministry of Science and Higher Education of the Russian Federation (No. AAAA-A18-118020190098-5, topic Electron and No. AAAA-A18-118020190095-4, topic Quantum) and was partially supported by grants from the Russian Foundation for Basic Research (Projects No. 19-52-18008 and No. 20-32-70019)

Application of Speckle Dynamics and Raman Light Scattering to Study the Fracture Features of Pipe Steel at High-cycle Fatigue

Despite a long history of research and a large number of publications, currently there are no methods for assessing and calculating the residual life of structural elements with their multi-cycle fatigue that would meet the requirements of engineering practice. In this regard, the role of physical methods to record the features of accumulation of local fatigue damage without stopping the operation or testing of various objects for fatigue increases. In the article two laser methods are used to study the origin of fatigue crack. Earlier, after testing for high-cycle fatigue of polished steel specimen with a Charpy notch, two zones of different sizes with different roughness were found near the notch. The first zone of 50x100 μm was located directly on the top of the notch. It consisted of inhomogeneities up to 10 μm in diameter and about 100 nm in height. In the center of the zone a macro-crack was discovered. The second zone with a diameter of 500-700 microns had a form of a hole (tie) with a depth of about 1 micron. Its center was located at a distance of 250-300 microns from the top of the notch. The aim of the work was to determine the formulation of inhomogeneities in a small zone and the sequence of the two zones’ occurrence. By using Raman microscopy, it is shown that the inhomogeneities are pieces of iron carbide. By the peculiarities of speckle image changes it is shown that the formation of two zones begins almost simultaneously. After the origination of a macro crack with a length of about 100 microns, a new plasticity zone at its top begins to form. Possible formation mechanisms of two zones are discussed. The disadvantages of the speckle method and the direction of further research are considered. © PNRPU.The authors thank I. S. Kamentsev, N.. Drukarenko, I. Tikhonova for help with sample preparation and fatigue testing. The work was carried out on the equipment of centers for collective use " Plastometry" of Institute of Engineering Science of Ural Branch of RAS and " Nanomaterials and Nanotechnology" of Ural Federal University with partial funding RFBR grant № 16-08-01077_a and act 211 of Government of the Russian Federation, agreement No. 02.A03.21.0006

Atomic and electronic structure of a copper/graphene interface as prepared and 1.5 years after

We report the results of X-ray spectroscopy and Raman measurements of as-prepared graphene on a high quality copper surface and the same materials after 1.5 years under different conditions (ambient and low humidity). The obtained results were compared with density functional theory calculations of the formation energies and electronic structures of various structural defects in graphene/Cu interfaces. For evaluation of the stability of the carbon cover, we propose a two-step model. The first step is oxidation of the graphene, and the second is perforation of graphene with the removal of carbon atoms as part of the carbon dioxide molecule. Results of the modeling and experimental measurements provide evidence that graphene grown on high-quality copper substrate becomes robust and stable in time (1.5 years). However, the stability of this interface depends on the quality of the graphene and the number of native defects in the graphene and substrate. The effect of the presence of a metallic substrate with defects on the stability and electronic structure of graphene is also discussed.Comment: 18 pages, 6 figures, accepted to Appl. Surf. Sc

Raman spectra of lead chalcogenide single crystals

Raman spectra of single crystals of lead chalcogenides (PbTe, PbSe, PbS) were studied at room temperature and ambient pressure. The structure of spectra for all compounds is rather similar showing the bands in one-and two-phonon range. Possible spectra identification is discussed

Raman study of coupled electronic and phononic excitations in LuB12

Electronic Raman scattering and optical phonon self-energies are studied on single crystals of LuB12with different isotopic composition in the temperature region 10–650 K and at pressures up to 10 GPa. The shape and energy position of the spectral peaks depend on the magnitude of the probed wave vector, temperature, and symmetry of excitations. We simulated experimental spectra using electronic structure obtained in the density functional theory and taking into account the electron-phonon scattering. The emergence of a broad continuum in the spectra is identified with the inelastic scattering of light from the electronic intraband excitations. Their coupling to non-fully symmetric phonon modes is the source of both the Fano interference and temperature-dependent phonon self-energies. In addition, long wavelength vibrations of the boron atoms are in nonadiabatic regime, so the electronic contribution to their self-energies provides a temperature dependence that is similar to the anharmonic contribution. Comparison of calculation and experiment allowed us to determine the coupling constant λ = 0.32, which gives correct critical temperature of the transition to the superconducting state. © 2017 Elsevier B.V

Raman study of coupled electronic and phononic excitations in LuB12

Electronic Raman scattering and optical phonon self-energies are studied on single crystals of LuB12with different isotopic composition in the temperature region 10–650 K and at pressures up to 10 GPa. The shape and energy position of the spectral peaks depend on the magnitude of the probed wave vector, temperature, and symmetry of excitations. We simulated experimental spectra using electronic structure obtained in the density functional theory and taking into account the electron-phonon scattering. The emergence of a broad continuum in the spectra is identified with the inelastic scattering of light from the electronic intraband excitations. Their coupling to non-fully symmetric phonon modes is the source of both the Fano interference and temperature-dependent phonon self-energies. In addition, long wavelength vibrations of the boron atoms are in nonadiabatic regime, so the electronic contribution to their self-energies provides a temperature dependence that is similar to the anharmonic contribution. Comparison of calculation and experiment allowed us to determine the coupling constant λ = 0.32, which gives correct critical temperature of the transition to the superconducting state. © 2017 Elsevier B.V

Structural, Optical and Electronic Properties of the Wide Bandgap Topological Insulator Bi1.1Sb0.9Te2S

Successful applications of a topological insulator (TI) in spintronics require its bandgap to be wider then in a typical TI and the energy position of the Dirac point in the dispersion relations to be away from the valence and conduction bands. In this study we grew Bi1.1Sb0.9Te2S crystals and examined their elemental composition, structural, optical and electronic properties as well as the electronic band structure. The high structural quality of the grown crystals was established by X-ray diffraction and Raman spectroscopy. Angular resolved photoelectron spectroscopy demonstrated a near parabolic character of the valence and conduction bands and a direct bandgap of 0.36 eV. The dispersion relations also revealed a Dirac cone, confirming the topological insulator nature of this material, with the position of the Dirac point being 100 meV above the valence band maximum. Far infrared reflectivity spectra revealed a plasma edge and two phonon dips. Fitting these spectra with theoretical functions based on the Drude-Lorentz model allows determination of the high frequency dielectric constant (41.3), plasma frequency (936 cm−1) and the frequencies of two infrared phonons (177.7 cm−1 and 77.4 cm−1). © 2021 Elsevier B.V.The reported study was funded by RFBR, project number 19-29-12061 . The part of optical research was carried out within the state assignment of Ministry of Science and Higher Education of the Russian Federation (theme "Spin" No AAAA-A18-118020290104-2 and No AAAA-A19-119081990020-8 and theme "Electron" No AAAAA18-118020190098-5 ). The study was also supported by the Russian Science Foundation (Project No. 17-12-01047 ) in the part of the crystal growth and state assignment of ISP SB RAS ( 0306–2019-0007 ) and IGM SB RAS. The Raman measurements were partially supported by the grant of the Russian Foundation for Basic Research (Project No. 19-52-18008 ). This work is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) through project-ID 258499086 – SFB 1170 (A01), the Würzburg-Dresden Cluster of Excellence on Complexity and Topology in Quantum Matter–ct.qmat Project-ID 390858490 – EXC 2147