Microwave spectroscopy of unconventional metals, superconductors and insulators

20世纪初，人们了解了非相互作用电子的量子行为后，半导体电子学发生了革命，目前社会正在从中获益。世界各地的许多研究人员都希望，当我们理解了一个更困难的量子问题——强相互作用电子系统的行为——时，电子材料领域将出现第二次革命。在这个阶段，挑战是根本性的：了解重要的电子特性是如何在相互作用的电子系统中出现的，并利用这些材料，使它们以受控的方式产生所需的特性。这些材料中的许多都表现出不同寻常的超导形式，在这种状态下，所有的电阻都消失了。例子包括铜高温超导体；所谓的“重费米子”物质，其中的电子似乎比正常情况重100到1000倍；以及最近发现的铁基超导体。目前，这些材料的超导机制还没有被很好地理解。此外，非超导态是不寻常的金属，对我们理解固体中的电子构成了一些最大的挑战。

Society is currently reaping the benefits of the revolution in semiconductor electronics that occurred after the quantum behaviour of noninteracting electrons was understood in the early 20th century. It is the hope of many researchers around the world that there will be a second revolution in electronic materials when we understand a far more difficult quantum problem - the behaviour of systems of strongly interacting electrons. At this stage the challenges are fundamental: to understand how the important electronic properties emerge in systems of interacting electrons, and to harness these materials so that they produce the desired properties in a controlled way. Many of these materials display unusual forms of superconductivity, a state of matter in which all electrical resistance vanishes. Examples include the cuprate high temperature superconductors; the so-called "heavy fermion" materials, in which electrons appear to be 100 to 1000 times heavier than normal; and the recently discovered iron-based superconductors. At present, the mechanism responsible for superconductivity is not well understood in any of these materials. In addition, the nonsuperconducting states are unusual metals that pose some of the greatest challenges to our understanding of electrons in solids.