Collective Quantum Phenomena

This is a diverse group, whose work focusses on two complementary areas: collective quantum phenomena, and mesoscopic quantum phenomena. The group is led by Prof Simons, Khmelnitskii, Cooper, Dr Lamacraft and Castelnovo.

Collective quantum phenomena are those which arise from the interplay between quantum mechanics and interactions in many-particle systems. There are a variety of such phenomena, ranging from superconductivity and magnetism to the quantum Hall effect. We apply phenomenological and model-based approaches, often involving techniques of quantum field theory, to unravel the physics behind such phenomena.

Semiconductor nanostructures provide several important model systems, requiring only the simplest models of electrons and holes moving in potential wells generated by bandstructure engineering. Despite this simplicity, these models show many exotic effects. These include the formation of collective states such as exciton and polariton condensates, the electronic Wigner crystal, and the quantum-Hall states.

We also study complex materials in which collective states occur. These require descriptions in terms of electrons moving in the periodic potential of the crystal lattice, often with multiple electronic bands and localised magnetic moments. Here collective states occur owing to both the direct interactions between electrons and the effects of the lattice. Contemporary examples of complex materials exhibiting collective states are high temperature superconductors and magnetic transition metal oxides.