X-ray absorption spectroscopy and optical reflectance measurements have been carried out to elucidate the evolution of the electronic structure in (Mg1−xAlx)B2 for x = 0.0, 0.1, 0.2, 0.3, and 0.4. The important role of B 2p σ hole states to superconductivity has been identified, and the decrease in the hole carrier number is quantitatively determined. The rate of the decrease in the hole concentration agree well with the theoretical calculations. On the other hand, while the evolution of the electronic structure is gradual through the doping range, Tc suppression is most significant at x = 0.4. These results suggest that the superstructure in (Mg1−xAlx)B2, in addition to the σ holes, can affect the lattice dynamics and contributes to the Tc suppression effect. Other possible explanations like the topological change of the σ band

We report the magneto-optical (MO) properties of compressively strained La0.7Sr0.3MnO3 (LSMO) thin films epitaxially grown on a LaAlO3 substrate. The magnetic force microscope images show the stripe magnetic domains, characteristic of films with the perpendicular magnetic anisotropy (PMA). The optical reflectance and transmittance of the samples were measured over a broad energy range from the far infrared through the ultraviolet. To extract the optical constants of the films, we analyzed all of the layers of this thin-film structure using a Drude-Lorentz model. From the parameters obtained, we compute the optical constants, such as frequency-dependent optical conductivity and the diagonal components of the dielectric tensor. Moreover, the MO polar Kerr spectra of the samples were measured in an applied magnetic field of 1.5T between 0.74 and 5.8eV. The off-diagonal components of the dielectric tensor were then calculated by analyzing Kerr rotation, ellipticity, and the determined diagonal elements of the dielectric tensor. These functions yield information about the spin-dependent electronic structures of the LSMO thin films. We observed several MO-active transitions above 2eV. These bands arise from the Mn-d(t2g) to Mn-d(eg) in the majority-spin channel and the onset of O-2p to Mn-d(eg) and O-2p to Mn-d(t2g) transitions in the minority-spin channel, in accord with the band-structure calculations. Most interestingly, their peak position and intensity are dependent on the film thickness, suggesting possible applications for tailoring MO responses in these PMA thin films.

We report on a systematic study of the thickness dependence of the optical properties of La0.7Sr0.3MnO3 thin films epitaxially grown on a LaAlO3 substrate. The x-ray powder-diffraction data indicate that the c-axis lattice constant is enhanced with decreasing the film thickness due to the compressive strain in the film plane produced by lattice mismatch. Magnetization curves show a decrease of the Curie temperature (TC) for decreasing thickness of films. Optical reflectance and transmittance measurements provide evidence that the position of Mn-O stretching mode shifts toward low frequency and the energy of the charge-transfer transition between O 2p and Mn 3d states increases with the decrease of film thickness. Most importantly, an analysis of the small-polaron absorption in the mid-infrared region shows that the polaron binding energy increases with decreasing the film thickness, suggesting that the strain dependence of TC mainly results from the strain-induced electron–phonon coupling.

X-ray absorption spectroscopy and optical reflectance measurements have been carried out to elucidate the evolution of the electronic structure in (Mg1-xAlx) B-2 for x=0.0, 0.1, 0.2, 0.3, and 0.4. The important role of B 2psigma hole states to superconductivity has been identified, and the decrease in the hole carrier number is quantitatively determined. The rate of the decrease in the hole concentration agrees well with the theoretical calculations. On the other hand, while the evolution of the electronic structure is gradual through the doping range, T-c suppression is most significant at x=0.4. These results suggest that the superstructure in (Mg1-xAlx)B-2, in addition to the sigma holes, can affect the lattice dynamics and contributes to the T-c suppression effect. Other possible explanations like the topological change of the sigma band Fermi surface are also discussed.

Highly optically active nonlinear bio-photonic crystalline and semicrystalline structures in living cells were studied by a novel multimodal nonlinear microscopy. Numerous biological structures, including stacked membranes and aligned protein structures are highly organized on a nanoscale and have been found to exhibit strong optical activities through second-harmonic generation (SHG) interactions, behaving similarly to man-made nonlinear photonic crystals. The microscopic technology used in this study is based on a combination of different imaging modes including SHG, third-harmonic generation, and multiphoton-induced fluorescence. With no energy release during harmonic generation processes, the nonlinear-photonic-crystal-like SHG activity is useful for investigating the dynamics of structure-function relationships at subcellular levels and is ideal for studying living cells, as minimal or no preparation is required.