Spin and charge in electrochemically doped oxides

过渡金属氧化物的物理学是当代凝聚态物质研究中最引人入胜和非常重要的课题之一。这些系统的物理性质是由几个自由度、电荷、自旋和电子的轨道状态的组合和竞争控制的。这种相互作用产生了丰富多样的基态。技术上重要的是，例如，高温超导铜和具有巨大磁阻的锰矿石。在这些体系中负责物理性质的一个重要参数是载流子的密度，它决定了过渡金属的氧化状态。在迄今为止报道的大多数实验研究中，载流子密度是通过通过固态反应部分取代阳离子或通过在受控氧气氛下通过热处理改变氧含量来调节的。因此，这些系统中的物理性质受到空间效应和无序性的很大影响。本研究计划的中心目标是研究过渡金属氧化物，其中电荷载流子密度是通过电化学调节和控制的。该方法是基于在晶格中提取和插入轻碱性金属离子，直接改变过渡金属的价态。它允许制备具有新物理性质的特殊氧化态。锂基过渡金属氧化物也被用作最先进的可充电电源。因此，深入了解这些系统的结构和电子特性也具有很高的技术价值。

The physics of transition metal oxides is one of the most fascinating and very important topics in contemporary condensed matter research. The physical properties of these systems are controlled by the combination and competition of several degrees of freedom, the charge, the spin and the orbital state of the electrons. This interplay gives rise to a rich variety of ground states. Technologically important are, e.g., the high temperature superconducting cuprates and the manganites with colossal magnetoresistance. One important parameter responsible for the physical properties in these Systems is the density of charge carriers which determines the oxidization state of the transition metal. In most experimental studies reported to date the charge carrier density is adjusted either by a partial substitution of the cations via a solid state reaction or by a modification of the oxygen content via a thermal treatment under a controlled oxygen athmosphere. Therefore the physics in these systems is considerably influenced by steric effects and disorder. The central objective of this research program is the study of transition metal oxides in which the charge carrier density is adjusted and controlled via electrochemistry. This method is based on the extraction and insertion of light alcaline metal ions in the crystal lattice which directly changes the valence of the transition metal. It allows the preparation of extraordinary oxidization states with new physical properties. Lithium based transition metal oxides are also used as state-of-the-art rechargable power sources. Therefore a deep understanding of the structural and electronic properties of these Systems is also of high technological interest.