Optical properties of SrTiO_3 at high temperatures

Picosecond nonlinear optical properties of SrTiO3 composite films doped with gold and nickel nanoparticles

Nanoparticles composite thin films formed by nanometer-sized gold and nickel particles embedded in SrTiO₃ matrices were fabricated on MgO single-crystal substrates by co-depositing the metal and ceramic targets using the pulsed laser deposition technique. The linear optical absorption properties were measured from 350 to 800 nm, and the absorption peak due to the surface plasmon resonance of Au metal particles was observed around 557 nm. The ultra-fast third-order nonlinear optical properties of the films were determined by a single-beam z-scan method at a wavelength of 532 nm with laser duration of 55 ps. The nonlinear refractive index n₂ and the nonlinear absorption coefficient β were determined, respectively, and the figure of merit χ⁽³⁾/α (with χ⁽³⁾ being the third-order nonlinear susceptibility and α the linear optical absorption coefficient) was discussed. Whether gold or nickel, metal particles have little effect on the figure of merit, but significantly affect the ratio of the real part to the imaginary part of χ⁽³⁾ [Reχ⁽³⁾/Imχ⁽³⁾]. The obtained Reχ⁽³⁾/Imχ⁽³⁾ of Au/SrTiO₃ is 1.43, which is more than 3 times as large as that of Ni/SrTiO₃.

Probing the spin pumping mechanism: exchange coupling with exponential decay in Y3Fe5O12/barrier/Pt heterostructures

It is widely believed that the mechanism for spin pumping in ferromagnet-nonmagnet bilayers is the exchange interaction between the ferromagnet and nonmagnetic material. We observe 1000-fold exponential decay of spin pumping from thin Y3Fe5O12 films to Pt across insulating barriers, from which exponential decay lengths of 0.16, 0.19, and 0.23 nm are extracted for oxide barriers having band gaps of 4.91, 3.40, and 2.36 eV, respectively. This archetypal signature of quantum tunneling through a barrier underscores the importance of exchange coupling for spin pumping and reveals its dependence on the characteristics of the barrier material.

Study of the dielectric properties near the band gap by VEELS: gap measurement in bulk materials

Measuring the band gap of bulk materials by valence electron energy loss spectroscopy (VEELS) is not straightforward. Mathematical procedures used to recover the single scattering distribution from raw data introduce artefacts in the signal, which complicate the gap measurement. In this work, we propose a method to overcome this and measure the direct band gap energy with an accuracy of +/-0.1eV. The method is tested on six crystalline wide-band gap materials: MgO, Ga(2)O(3), SrTiO(3), ZnO, BN and GaN.