The joint development of a new, miniaturised molecular-beam epitaxy (MBE) system on the I05 beamline by the University of Oxford and Createc GmbH (Erligheim, Germany) was the catalyst for research into the electronic structure of thin films of Europium monoxide (EuO). The highly 3D nature and air-sensitivity of EuO makes it hard to study by angle-resolved photoemission from single crystals, but the new facility allows a freshly-grown surface to be transferred directly to the beamline, under good vacuum conditions.
This enabled Jon Riley, studying for a PhD with Diamond and the University of St Andrews, to start experimenting with doping EuO films with Gadolinium (Gd). On its own, EuO is a ferromagnetic insulator, but Gd doping adds extra electrons. The experimental results, together with supporting theoretical work from researchers at the University of Oxford, have recently been published in Nature Communications and point to an intriguing polaronic state, arising from the coupling of the induced charge carriers to the conduction-electron plasmon excitations.