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

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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.