The electronic structure of strongly correlated electron systems

强相关电子系统展示了一些最有趣的物理特性，未来可能应用于电子设备、可持续能源、生物医学设备、交通运输，甚至量子计算。由过渡金属和稀土化合物（如氧化物）制成的材料通常表现出极端特性，如高温超导性、高热电功率、高介电常数、巨磁电阻等等。这些材料不同于传统的半导体，如硅或简单的金属，如铝，其中电子在原子之间移动的电荷在决定应用中起着重要作用。另一方面，过渡金属氧化物通常是电绝缘体和磁性的，因为电子之间的相互排斥作用很强。然而，化学取代可以将这种磁性绝缘体转变为高温超导体（诺贝尔奖1988），并导致其性质的其他戏剧性变化。支配它们行为的基本物理学仍然是现代科学研究中最大的智力挑战之一。这里，自旋和轨道自由度以及它们与电子的电荷自由度的相互作用起着至关重要的作用。需要新的对这些自由度敏感并适用于薄膜、界面和异质结构等纳米尺度结构的实验方法。

Strongly correlated electron systems exhibit some of the most interesting physical properties for possible future applications in electronic devices, sustainable energy, biomedical devices, transportation and perhaps even quantum computing. Materials made of transition metal and rare earth compounds such as the oxides are examples often exhibiting extreme properties such as high temperature superconductivity, high thermoelectric power, high dielectric constants, collassal magneto resistance and many more. These materials are different from conventional semiconductors like Si or simple metals like Al in which the charge of the electrons moving in amongst atoms plays the important role in determining the applications. Transition metal oxides on the other hand often are electrical insulators and magnetic because of the strong repulsive interaction between the electrons. However chemical substitution can turn such magnetic insulators into high temperature superconductors ( Nobel Prize 1988 ) and cause other dramatic changes in their properties. The basic physics governing their behaviour remains one of the biggest intellectual challenges of modern scientific research. Here the spin and orbital degrees of freedom and their interplay with the charge degrees of freedom of electrons play essential roles. New experimental methods are needed which are sensitive to these degrees of freedom and applicable to nanometer scale structures such as in thin films, interfaces and heterostructures.