Mark Ellerby
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Mark Ellerby (CMMP) - Research

Our research interests mainly concern the properties of intercalated materials and electronic liquids. This research involves a variety of experimental and computational techniques, including low temperature transport studies, magnetometry, neutron and X-ray scattering. Examples of some of our current research projects are given below.

Superconducting Graphite Intercalates

Low dimensionality is generally considered as a necessary ingredient for high superconducting transition temperatures. Surprisingly, perhaps, systems based on graphite have received relatively little attention in this context. Introducing metal atoms between the carbon layers can tune the interlayer spacing and charging of the graphite host through a variety of electronic ground states. One such ground state is superconductivity, which is not present in pure graphite. Here we report the discovery of superconductivity in the intercalation compounds C6Yb and C6Ca, with transition temperatures of 6.5 and 11.5 K, respectively. These critical temperatures are unprecedented in graphitic systems and have not been explained by a simple phonon mechanism for the superconductivity. This discovery has already stimulated several proposals for the superconducting mechanism that range from coupling by way of the intercalant phonons through to acoustic plasmons. It also points towards the potential of superconductivity in systems such as carbon nanotubes.

Electronic Solutions

Electronic Solutions are formed when a metal dissolves in a polar solvent without chemical reaction, the prototypical solvent being liquid ammonia. This process reversibly releases excess electrons into the liquid, creating a solution of fundamental particles! The presence of these electrons results in liquids that are truly extraordinary, and which have a unique combination of properties which are yet to be exploited. For example; very low density, very low viscosity, a deep pseudoeutectic (giving the lowest temperature liquid metals), a concentration driven metal-nonmetal transition, liquid-liquid phase separation, highly conducting glassy phases, high electrical conductivity, and exceptionally high redox reactivity.
Our recent neutron and X-ray scattering experiments on these liquids have illucidated the structure and dynamics of these extraordinary liquids, including the solvation of the electron (polaraons and bipolarons) and the mechanisms of electron delocalisation. In addition, we have used these liquids as solvents for carbon nanostructures (fullerides) - and shown how C60 is solvated (Dr Christopher Howard).

University College London - Department of Physics and Astronomy - Gower Street - London - WC1E 6BT - Telephone: +44 (0)20 7679 7155 - Copyright © 1999-2005 UCL

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