Ultra-Sensitive Measurements of Electronic Structure and Correlations in Magnetic Fields up to 25 Tesla

虽然很多教科书上的凝聚态物理都是用不相互作用的电子来描述的，无论是在简单的金属中还是在简单的绝缘体中，但在这两类之间的界面上，概念上出现了大量新的物理学，比如过渡金属氧化物。我们提出了一个研究计划来研究这些相关材料的电子结构。我们主要的实验技术（所谓的de Haas-van Alphen效应）实际上就是让电子绕圈运动。这是通过施加一个大磁场来实现的：就像一个条形磁铁固定在传统的电视屏幕上会使产生电视图像的电子偏转一样，一个更大的磁场会使电子绕一个紧密的圆圈运行。金属中的电子也是如此，只不过它们的轨道不再是圆形的。我们无法用肉眼看到一块金属的内部，但利用复杂的量子干涉效应，我们仍然可以推断出这些轨道的形状（以及金属内部电子的质量，有趣的是，金属内部电子的质量可能与金属外部电子的质量不同）。这些效应相当微妙，人们需要非常大的磁场、非常低的温度和非常灵敏的探测系统来观察它们。我们打算制造一个比头发丝还小的传感器，并使用世界上最强的磁铁，包括即将在剑桥安装的磁铁，来提高我们测量信号的大小。我们将使用这个新的装置，连同我们现有的装置，来研究过去几年出现的一些最有趣的材料——其中包括那些尚未解释的超导体，以及如果你挤压它们就会开始导电的绝缘体。

While much of textbook condensed matter physics is described in terms of non-interacting electrons, either in simple metals or in simple insulators, a whole host of new physics arises in materials conceptually at the interface between those two classes such as transition metal oxides. We propose a research programme to investigate the electronic structure of such correlated materials.Our main experimental technique (the so-called de Haas-van Alphen effect) involves quite literally sending electrons around in a circle. This is achieved by applying a large magnetic field: just as a bar magnet held to a conventional TV screen will deflect the electrons that create the TV image, a larger magnetic field will cause the electrons to orbit in a tight circle. The same happens to electrons in metals - except that their orbits are then no longer circular. We cannot look inside a piece of metal with our own eyes, but using sophisticated quantum interference effects, we can still infer the shape of these orbits (as well as the mass of the electrons inside the metal which, intriguingly, can differ from the electron mass outside it). These effects are rather subtle, and one needs very large magnetic fields, very low temperatures, and very sensitive detection systems to observe them. We propose to build a sensor smaller than a human hair, and use the world's strongest magnets including one that is soon to be installed in Cambridge, to boost our signal size for these measurements. We will use this new setup, along with our existing one, to work on some of the most intriguing materials that have emerged in the past few years - amongst those yet unexplained superconductors, and insulators that start to conduct if you squeeze them.