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In this article, we compare the excitation wavelength dependence of the polarization anisotropy (ρ) of an internal field induced Raman scattering signal in individual bare InAs and InAs/GaSb core-shell nanowires. The measured value of ρ of the Raman scattering intensity for InAs/GaSb core-shell nanowires has a minimum at ∼500 nm, while for the bare InAs nanowire, the value of ρ monotonically increases over the same range of wavelengths. We have modeled the scattering intensities of both systems by considering the joint role of Raman tensor components and confinement of electromagnetic radiation inside the nanowire at two orthogonal polarization configurations of the electromagnetic radiation. The theoretical results allow us to understand that the observed behavior of ρ is related to the nanowire geometry and to the difference in the wavelength dependence of the dielectric constants of InAs and GaSb. This work shows the possibility of manipulating the polarization anisotropy by selecting suitable diameters and materials for the core and the shell of the nanowire. We also report a six-fold increase in Raman scattering intensity due to the GaSb shell on InAs nanowires. [ABSTRACT FROM AUTHOR]

Abstract: An internal field induced resonant intensity enhancement of Raman scattering of phonon excitations in InAs nanowires is reported. The experimental observation is in good agreement with the simulated results for the scattering of light under varying incident wavelengths, originating from the enhanced internal electric field in an infinite dielectric cylinder. Our analysis demonstrates the combined effect of the first higher lying direct band gap energy (E 1) and the refractive index of the InAs nanowires in the internal field induced Raman scattering. Furthermore, the difference in the relative contribution of electro-optic effect and deformation potential in Raman scattering of nanowires and bulk InAs over a range of excitation energies is discussed by comparing the intensity ratio of their LO and TO phonon modes. [Copyright &y& Elsevier]

Half-metallic ferromagnetic full Heusler alloy NiFeMnSn is a promising material in spintronic device fabrication as it carries high spin polarization and high Curie temperature (Tc = 405 K). Understanding electronic excitations in a spin-polarized band structure is essential for the further use of this material in spin-based devices and to optimize the spin-dependent electronic structure in related compounds. In this Letter, we report electronic Raman scattering of NiFeMnSn with spectral signatures at a higher wavenumber than expected from the calculated phonon modes of the system. Temperature-dependent Raman spectroscopy demonstrates a non-monotonic behavior of the Raman shift with temperature across Tc. The orbital resolved electronic density of states and electronic band structure for both spin channels of the system, as obtained from the first principles density functional theory calculations, suggest that the observed Raman signatures originate from the Fe d orbital and its splitting due to the crystal field near the Fermi level. Furthermore, a strong magnetic field dependence of the spectral profile is observed. The study not only exhibits electronic Raman scattering in a Heusler alloy compound, which was unexplored to date, but also establishes Raman scattering as a promising probe to study the orbital-resolved partial density of states in the band structure near the Fermi level of a Heusler alloy. [ABSTRACT FROM AUTHOR]

Single crystals of the iron-pnictide compound BaFe 2 (As 1 − x P x) 2 for x ∼ 0.23, with a doping concentration near quantum criticality and enhanced nematic fluctuating state in the doping-temperature phase diagram, have been studied. Transport measurements confirm the presence of a magneto-structural transition at 60 K from the tetragonal to the orthorhombic phase, followed by a superconducting transition below 16 K. Micro-Raman spectra of the compound exhibit a phonon mode at 211 cm−1 and two broad modes (BMs) at 515 cm−1 and 635 cm−1, which corresponds to an energy difference of 15 meV. The temperature dependent Raman measurements reveal that the intensity of these BMs drop over the temperature range between 80 K and 300 K. In the non-superconducting state, strong anisotropic behaviour is observed for these BMs in polarization dependent Raman scattering. Electronic structure calculations for doped and undoped BaFe 2 As 2 show that while Fe d x z and d y z orbitals do not split in the tetragonal phase, the splitting energy is 13.5 meV in the orthorhombic phase of the doped system, which is reasonably close to the experimentally observed value of the energy separation of the BMs. We believe that the reported BMs are consistent with the signature of electronic Raman scattering involving the crystal field levels of d -orbitals of Fe2＋ due to local breaking of the C 4 symmetry in the doped system. • Local symmetry breaking in tetragonal phase of P doped BaFe 2 As 2 near quantum critical point. • Signature of crystal field splitting using temperature dependent micro Raman spectroscopy. • Calculation of Fe d orbitals split energies in local orthorhombic phase using DFT. [ABSTRACT FROM AUTHOR]

Abstract: The formation of strained layers and a non-monotonic evolution of strain in high energy (100MeV) silver ion (Ag7+) irradiated undoped semi-insulating GaAs are observed and analyzed using Raman scattering and high resolution X-ray diffraction (HRXRD) measurements. At low fluence, compressively strained layers are formed, whereas, with increase in fluence both compressive and tensile strains appear as observed from HRXRD measurements. Further, at low fluence, the change in compressive strain with increase in fluence is found to be sharper than what is observed at higher fluence, thereby suggesting a critical fluence value, beyond which there is a simultaneous generation and annihilation of vacancy type defects. The initial blue shift and subsequent relative red shift beyond above critical fluence in the Raman peak also qualitatively reveal non-monotonic evolution of strain in this case. Finally, we demonstrate the sensitivity of Raman spectroscopy in detecting the decrease in lattice ordering in the crystal in the low fluence regime, below the detection limit of Rutherford back-scattering channeling (c-RBS) measurements. [Copyright &y& Elsevier]

Highlights: [•] PCA of Raman data discriminates molecular structure of HEWL protein and fibrils. [•] SD of scores in PCA plots determines variability in the structure within a species. [•] Overall structure significantly differs for fibrils grown at different pH values. [•] Overall structure of fibrils grown at different pH values in Cu(II) has similarity. [•] Presence of Cu(II), inhibits the formation β-sheet component in HEWL fibrils. [ABSTRACT FROM AUTHOR]