In contrast to conventional materials, where physical properties such as heat capacity or electrical resistance are volumetric effects, which can be described by classical equations, this does not hold anymore for quantum materials, as their properties are significantly influenced by the quantum mechanical wave function of the electrons. Quantum materials exhibit unique physical properties such as super-conductivity and topological insulation.

In particular 2D quantum materials have considerable technological potential; for example, they could replace conventional transistors with significantly more energy-efficient transistors in the future. Due to its high sensitivity, the electron diffraction method is ideally suited for investigating such extremely thin structures, often consisting of only one or a few monolayers of atoms, with extremely high spatial resolution. Due to the extremely short duration of the electron pulses at REGAE, not only can static structural determinations be carried out, but dynamic processes such as ‘switching processes’ in these materials, in which they abruptly change their physical properties, can also be investigated at the atomic level with a time resolution in the femtosecond range. These ‘switching processes’ are based on phase transitions in the materials. The phase transitions can be induced in various ways. Of particular interest is the selective excitation of individual transitions with short laser pulses in the THz range. The generation and provision of the appropriate THz excitation for electron diffraction experiments is an important focus of our work at REGAE (Figure 2). Due to the low beam damage, the sample is damaged so little during the investigations that many measurements can be carried out on a single sample and the sample does not have to be constantly replaced, as is often necessary with comparable measurements at XFELs.

In addition, the use of high-energy MeV electrons and their outstanding material penetration properties at REGAE not only allows individual isolated 2-D layer structures to be investigated, but also fully functional circuits (‘devices’) with attached electrodes to be characterized under operating conditions.