Normal state properties of cuprates superconductors under high pressure

The microscopic origin of superconductivity in cuprate high temperature superconductors remains a major unresolved problem in condensed mater physics. Key to solving this fundamental physics problem is to understand the normal state out of which the superconductivity develops. This normal state has many properties which are different from conventional metals, and its nature evolves markedly as the electron concentration (hole-doping) of the material is varied. In certain ranges of doping and temperature, other phases are found to compete or exist alongside the superconductivity. These are known as the pseudogap and charge density wave phases. Determining how these phases interact with the superconductivity has been a major subject of enquiry. It is thought that fluctuations of these phases can enhance/cause superconductivity or instead, statically ordered phases destroy/diminish superconductivity.
Tuning of the cuprate materials through their different phases is usually achieved using charge doping. In this project, we will instead use hydrostatic pressure and uniaxial stress to tune the materials. It is known that hydrostatic pressure can make very large changes in the superconducting critical temperature although there is little understanding of its exact mechanism. It is possible that part of its effect results from charge transfer but there is also a less well understood structural element. For example, for most cuprates, the highest superconducting transition temperature is only reach under high hydrostatic pressure.
Here we will study the normal state transport properties: electrical resistivity, Hall effect, thermoelectric power and Shubnikov de-Haas effect of cuprate superconductors such as YBa2Cu3O6+x and Tl2Ba2CuO6+x, in order to understand the mechanism of how pressure effects the superconducting critical temperature. New high pressure / strain apparatus will be developed to achieve these aims. Experiments will be conducted in superconducting magnetics in Bristol (up to 16T) and at high magnetic field facilities (EMFL facilities in Nijmegen and Toulouse, and NHMFL Tallahassee).

The Institute of Physics has estimated that physics-dependent businesses directly contribute 8.5% to the UK's economic output, employ more than a million people and generated exports amounting to more than £100bn in 2009. They go on to say: "It is important for businesses to have access to a range of highly skilled (and motivated) individuals capable of thinking 'outside of the box', particularly physics-trained postgraduates due to the highly numerate, analytical and problemsolving skills that are acquired during their training." If funded, the graduates of this CDT will have such skills and motivation. We would hope that this would significantly contribute towards satisfying the UK's need for trained scientists, particularly in the field of condensed matter physics. The impact would go further than this. By working more closely with industry and other partner organisations, we would reshape the conventional PhD programme to improve the experience for all.

In addition to the training aspect of the CDT there would be an important research impact. The Universities of Bristol and Bath have many world-leading researchers across the condensed matter field. By working with the high-quality students that we hope to recruit into the programme we will produce significant cutting edge research in condensed matter. The research would bear on some of the grand challenges facing condensed matter physics such as: understanding the emergence of new phenomena far from equilibrium; the nanoscale design of functional materials such as graphene; and harnessing quantum Physics for new technologies. Ultimately, this would contribute to improvements in many technologies, for example, energy or data storage technology.