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

光学技术如非弹性光散射、光致发光和红外干涉测量法对发展基础科学和解释固体中的微观相互作用非常有用。我们使用这些技术来更好地理解以下机制和微观性质：a)-最近发现的锰矿中巨大的磁电阻R(1-x) a (x)MnO3 (R =稀土和a =Ba, Sr, Ca)，其中在施加磁场后观察到异常大的电阻率变化。这些材料一方面从基本观点来看是有趣的，因为电荷、自旋和晶格离子是强耦合的，引起了凝聚态物质中许多当前感兴趣的物理现象和相变。另一方面，它们在磁记录介质传感器和自旋极化电子器件中提供了潜力。b)-高临界温度超导体，如R(2-x)Ce(x)CuO4，其特征是在Tc以下无电阻和完美的抗磁性。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)-基于稀土的光学器件，如固态激光器和通过掺杂稀土离子的氧化物（例如Nd: YVO4和Yb:Y2SiO5）获得的光学存储器。在前一种材料中加入了稀土离子（Pr, Nd, Sm…）。光散射和红外光谱构成了我们探测离子振动和4f稀土电子能级的工具。这些能级被用作局部探针来探测电子-电子、电子-离子和离子-离子之间的各种电和磁相互作用。利用量子力学的形式，我们建立了各种电和磁相互作用的模型。这些相互作用作为温度、外加磁场、静水压力和掺杂的函数被调整和修改。在这些材料中，我们在不同和对比特征占上风的小域中检测相分离。对其性质的基本理解将使这些材料在高科技光学和电子领域的应用成为可能。

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.