Review: “An elusive factor of 2: The ongoing quest for a room temperature superconductor”
Tuesday 06 January, 2015
Superconductors can be described as materials that exhibit zero electrical resistance and the latter is dependent on temperature. At high temperature the atoms within a material have more thermal vibration and therefore will not allow electrons to flow as easily when an electrical current is applied. However, when the material is cooled down to a certain (critical) temperature (0-120 K) electrons spontaneously pair up making them effectively immune to thermal vibrations and the complete disappearance of resistance to their flow. However, the defining characteristic of superconductors is that they expel magnetic fields from their interior after transition from the normal to superconducting state (Meissner effect), and this responsible for phenomenon like magnetic levitation.
Image: A representation of a laser driven lattice distortion
On December 1, Dr. Stephen Clark took us on a journey exploring the world of superconductivity from its discovery in 1911 to the current challenges it faces in the 21st century. He explained that superconductivity was discovered by chance during the quest to reach low temperatures and liquefying “permanent” gases such as helium, nitrogen, hydrogen.
Over the following decades, other elements of the periodic table –as well as compounds and alloys- were found to be superconductors at different critical temperatures. In the 1980’s, a new class of superconductors arrived: the cuprate-perovskite ceramics of the type ABO3, where B is copper (Cu), O being oxygen and A can be rare-earth elements likelanthanum (La),barium (Ba),or yttrium (Y) for example. These materials are known as high critical temperature superconductors as superconductivity can be reached at 90K rather than 0-23K. Today, we can find materials in this class with critical temperatures around 120-130K which have received a great deal of attention because they can be maintained in the superconducting state with liquid nitrogen (77 K) and are therefore simpler to use and cheaper than conventional superconductors.
Where do we find superconductors being used? In fact they are very useful in our daily lives. We find superconducting magnetsused in most hospitals such as NMR, MRI, as wellin analytical chemistry instruments likemass spectrometers, particle accelerators, etc. However, many more application could come in the future with room temperature superconductors. For example, Stephen Clark explained that everyday computing processing power has stayed in the gigahertz range due to the limitations of current transistor technology whilethe creation ofsupertransistorscould instead reachterahertzfrequencies. Other examples include the storage devices, electric power transmission and cables with zero power loss. The importance and usefulness of close to room temperature superconducting materials is attested to by the thousands of academic papers published in this field every year.
In working towards the close to room temperature goal Stephen Clark and his collaborators are taking a different route from many. They are currently working on forcing materials to exhibit superconductivity through the use of lasers that can selectively cool the specific degree of freedom of the material that is crucial to it superconductivity, rather than cooling the entire material.
Stephen Clark is Career Development Fellow in Quantum Networks at Keble College and Senior Researcher at the Department of Atomic and Laser Physics, Clarendon Laboratory, University of Oxford. The major themes for his research revolve around non-equilibrium phenomena in many-body systems ranging from ultra-cold atoms to strongly correlated electron materials. Stephen is a key member of the ASC Networks Cluster.