High resolution differential heat capacity measurements of cuprate superconductors and other correlated electron systems

当许多元素、合金或金属间化合物被冷却到一定的过渡温度以下时，它们的电阻就会突然消失，成为被称为超导体的完美导体。其中一些超导体可以携带大电流（每平方厘米导体超过一百万安培），而功耗可以忽略不计。合金，特别是NbTi和金属间化合物，特别是Nb3Sn，自20世纪50年代末以来一直用于产生强磁场。超导的另一个有用和迷人的应用是生产微型SQUID（超导量子干涉装置），它对通过一平方厘米的磁通量（小于地球磁场的十亿分之一）非常敏感。1986年，诺贝尔奖得主贝德诺茨和穆勒发现了一类新的铜超导体。这些材料含有氧化铜层，其超导温度比以前的材料高得多，远高于液氮的沸点。他们的发现引发了巨大的研究活动，旨在了解这种意想不到的高转变温度的起源，并掌握这些包含至少四种元素的复杂材料，以便它们可以用于实际设备。最著名的化合物之一，钇钡铜氧化物，现在已经发展到可以生产千米长的超导带的阶段，以及在液氮温度下工作的SQUID设备。尽管世界上许多高度敬业的科学家付出了巨大的努力，但在理解铜超导性和在有用的设备中利用其特性方面，仍有许多工作要做。在过去的15年中，英国研究工作的亮点之一是J.W. Loram博士和他的同事在测量几种典型铜系统的热容量方面的独特实验工作。本提案旨在扩展这项工作，帮助解决几个重要和有争议的理论问题，同时获得有关这些化合物中超导性强度的有用经验知识。这项实验技术还将应用于另一类不寻常的电子材料，即重费米子化合物，大量的实验技术将传授给年轻的研究人员。

When many elements, alloys or intermetallic compounds are cooled below a certain transition temperature their electrical resistance suddenly disappears, they become perfect conductors known as superconductors. Some of these superconductors can carry large currents (exceeding one million amps per square centimetre of conductor) with negligible power dissipation. Alloys, especially NbTi and intermetallic compounds, especially Nb3Sn have been used since the late 1950s for generating high magnetic fields. Another useful and fascinating application of superconductivity is the production of miniature SQUID (superconducting quantum interference devices) that are uniquely sensitive to magnetic flux / less than a billionth of the Earth's magnetic field passing through a square centimetre.In 1986 the Nobel Prize winners Bednorz and Muller discovered a new class of cuprate superconductors. These contain copper oxide layers and are superconducting up to much higher temperatures than previous materials, well above the boiling point of liquid nitrogen. Their discovery triggered tremendous research activity aimed at understanding the origin of such unexpectedly high transition temperatures and at mastering these complex materials, that contain at least four elements, so that they can be used in practical devices. One of the best-known compounds, yttrium barium copper oxide has now been developed to the stage where km lengths of superconducting tape can be produced, as well as SQUID devices, working at liquid nitrogen temperatures.Despite intensive efforts by many highly committed scientists throughout the world there is still much to be done, both in understanding cuprate superconductivity and in harnessing their properties in useful devices. One of the highlights of the U.K. research effort over the past 15 years has been the unique experimental work Dr. J.W. Loram and colleagues in measuring the heat capacity of a several typical cuprate systems. The present proposal seeks to extend this work, helping to resolve several important and controversial theoretical questions, and at the same time obtaining useful empirical knowledge regarding the strength of the superconductivity in these compounds.The experimental technique will also be applied to another class of unusual electronic materials known as heavy fermion compounds, and substantial experimental know-how will be passed on to younger researchers.