Optical studies of manganites, superconductors and laser materials - études optiques des manganite, supraconducteurs et matériaux laser

非弹性光散射、光致发光和红外干涉等光学技术对于发展基础科学和解释固体中的微观相互作用是非常有用的。我们利用这些技术来更好地理解：A)-最近在锰氧化物R(1-x)A(X)MnO_3(R=稀土，A=Ba，Sr，Ca)中发现的巨磁电阻，其中随着磁场的施加，观察到了异常大的电阻率变化。一方面，从基本的观点来看，这种材料是有趣的，因为电荷、自旋和晶格离子是强耦合的，导致了许多物理现象和当前对凝聚态感兴趣的相变。另一方面，它们在磁记录介质传感器和自旋极化电子设备中具有潜力。B)-高临界温度超导体，例如R(2-x)Ce(X)CuO4，其特点是没有电阻，在T_c以下完全抗磁。它们是重要的材料，通常用于无损耗的电流传输、高磁场产生和检测非常弱磁场的设备。C)-通过掺杂稀土离子(如：NdYVO4和Yb：Y2SiO5)获得的固体激光器和光学存储器等稀土基光学器件。在前者材料中，稀土离子(Pr，NdSm……)是一家公司。光散射和红外光谱是我们用来探测离子振动和4f稀土电子能级的工具。这些能级被用作局部探测器来检测电子-电子、电子-离子和离子-离子之间的各种电和磁相互作用。然后，利用量子力学的形式，我们对各种电和磁相互作用进行了建模。这些相互作用是作为温度、外加磁场、流体静压和掺杂的函数来调节和修改的。在这些材料中，我们在小区域中检测到相分离，在这些区域中，不同和对比的特征占优势。对其性质的基本了解将使这些材料在高科技、光学和电子学中得到应用。

Optical techniques such as inelastic light scattering, photoluminescence and infrared interferometry are very useful to develop fundamental science and to explain microscopic interactions in solids. We use these techniques to better understand the mechanisms and microscopic properties of: a)-recently discovered colossal magnetoresitance in manganites R(1-x)A(x)MnO3 (R = rare earth and A=Ba, Sr, Ca) where an unusually large change of resistivity is observed  following the application of magnetic field. Such materials are on one hand interesting from a fundamental viewpoint since charge, spin and lattice ions are strongly coupled giving rise to numerous physical phenomena and phase transitions of current interest in condensed matter. On the other hand, they offer potential in magnetic recording media sensors and spin polarized electronics. b)-high critical temperature superconductors, e.g. R(2-x)Ce(x)CuO4, characterized by absence of resistance and perfect diamagnetism prevalence below Tc. They are important materials typically for current transport without losses, for high magnetic field generation and for devices that detect very weak magnetic fields. c)-rare earth based optical devices such as solid state lasers and optical memories obtained by doping oxides with rare earth ions (e.g. Nd: YVO4 and Yb:Y2SiO5).In the former materials, rare earth ions (Pr, Nd, Sm...) are incorporated. Light scattering and infrared spectroscopy constitute our tools to detect the ions vibrations and the energy levels of the 4f rare earth electrons. These levels are used as local probes to detect the various electrical and magnetic interactions between electron-electron, electron-ion and ion-ion. Using quantum mechanics formalism, we then model the various electrical and magnetic interactions. These interactions are tuned and modified as a function of temperature, applied magnetic field, hydrostatic pressure, and doping. In these materials, we detect phase separation in small domains where different and contrasted characteristics prevail. A basic comprehension of their properties would allow applications of these materials in high technology optics and electronics.