'Metals without electrons' seems like a paradox, for the very notion of a metal, we learn, relies on electrons becoming delocalized from their atomic hosts to form a conduction sea. Yet including the effects of quantum mechanics and inter-particle interactions one often finds that the 'particles' which characterize a strongly correlated quantum fluid can be very different from the initial ingredients in the problem.
In bringing atoms together to form a crystalline solid, for example, one finds that the low energy properties are best described in terms of a gas of weakly interacting Bose particles – phonons – which are the quanta of the lattice vibrations.
It should therefore be a surprise that we can very often think of the electrons in a metal simply as a non interacting gas of electrons. The reason this works so well was first formulated by Landau in the 1950s in his Fermi-liquid theory. He showed that really this picture is describing electron-like 'quasiparticles' which share many of the properties of electrons but are in fact complex many-body approximations to eigenstates of the system. These approximate eigenstates become an increasingly better approximation as the temperature (or other relevant energy-scale) is reduced.
Recent years have seen tremendous advances in material science which has resulted in the discovery of many new types of complex metals. Among them include the various oxide metals such as high temperature cuprate superconductors, the ruthenates, the manganate CMR materials, as well as f electron alloys such as UBe13 picture above. Many of these seem to lie outside Landau's Fermi liquid paradigm: the electron-like quasiparticle does not appear to describe their properties. It seems that we need a new picture of the correlated quantum fluid to describe these new materials. Our research is focused towards this endeavour.
For some general information on current topics in physics of strongly correlated electron systems, see
- Quantum Matter - the challenge to theory
An invited talk given at the Institute of Physics Einstein Centenial Meeting (Physics - a century after Einstein)
- New states of correlated electrons
The Future Conference.
Contemporary Physics 40, 95-115 (1999)
Current research work by the group in this area includes the theory of quantum critical points, and spin-charge separation in Luttinger liquids.