Normal and superconducting state electronic structure of iron based superconductors

Completed

Not Energy Related(Not Energy)
Other Power and Storage Technologies(Electric power conversion)
Other Power and Storage Technologies(Electricity transmission and distribution)

Basic and strategic applied research

PHYSICAL SCIENCES AND MATHEMATICS (Physics)

Not Cross-cutting

Professor A Carrington
Physics
University of Bristol

Standard

EPSRC

01 September 2010

31 August 2014

48 months

£557,003

Materials sciences

South West

NC : Physical Sciences

Professor A Carrington, Physics, University of Bristol

Superconductivity is a fascinating phenomenon giving rise to quantum coherence over vast distances (several hundred kilometres of wire). It also has many valuable practical applications - basically anything which uses electricity can in principle benefit from superconducting technology. The most obvious applications are lossless power transmission cables, very high efficiency power transformers and generators. These applications have been promised since the early days of superconductivity atthe start of the 20th century, but are only now becoming practical 20 years after the discovery of materials which superconduct above the boiling point of liquid nitrogen (77 Kelvin).The discovery and refinement of new superconducting materials benefits immensely from improving our understanding of their fundamental physics - most importantly the reason for the formation of the coherent superconducting state. Despite more than twenty years of research there is still no consensus as to the mechanism of high temperature superconductivity in the famous copper oxide (cuprate) materials. The discovery just over one year ago of high temperature superconductivity in material containing the element iron was very surprising as the magnetism normally associated with iron is highly detrimental to the formation of the superconducting state. These materials are of great interest from a point of view of both the fundamental physics and potential applications. The former stems from severalkey similarities (and differences) with the cuprate superconductors - perhaps making these materials the 'Rosetta stone' that can be used to understand how electronic mechanisms can produce a high temperature superconducting state. The latter from the fact that some materials continue to superconduct even when subjected to the world most intense magnetic fields in excess of 60T.The research in this proposal aims to further our understanding of high temperature superconductivity and inparticular iron-based superconductors by pursuing two related research paths. One path will address the nature of the superconductivity itself. By measuring the influence of temperature on the density of superconducting electrons, through measurement of properties such as the magnetic penetration depth (i.e., the fundamental ability of a superconductor to screen out an applied magnetic field) we can learn the microscopic properties of the electrons which carry the superconducting current. Theother path will be to study the properties of the 'normal' metal state. By applying large magnetic field, the superconductivity can be suppressed (effectively turned off) and then we can study the non-superconducting normal metallic state of the materials. In sufficiently high field, characteristic periodic oscillations of the magnetisation as a function of field (the de Haas-van Alphen effect) reveal the exact momenta of the electrons that carry current and how this momentum variesas a function of direction. This determination of the 'electronic structure' of a metal is akin to knowing its DNA. By studying how this normal state electronic structure varies in the different materials and how this influences the superconducting properties it will be possible to build up a theoretical picture of the mechanism of high temperature superconductivity

24/12/09