Control of condensed matter has been one of the frontiers in the science and technology of the past century. Harvesting energy, transporting, storing and processing information and controlling catalysis are only a few of the great achievements that have fuelled a phenomenal economic and social progress in the recent decades. It is important to recognize that these advances have, arguably, primarily been driven by progress in materials science and technology. Yet, our current ability to control the functionalities of matter are rapidly being saturated, becoming insufficiently fast, dissipating too much heat and working on too long length scales. It is safe to say that one grand challenge is the development of a new generation of materials that can be controlled at ultrahigh speeds by rapid stimulation (e.g. by light), leading to new concepts for micro and nano-device applications. To this end, the new class of materials generally referred to as strongly correlated electron systems promise important advances. Several aspects make these compounds remarkable.
First and foremost, they exhibit macroscopic quantum phenomena at very high temperatures. This descends directly from the fact that interactions between microscopic degrees of freedom occurs on very high energy scales, making emergent phase robust against violent thermal fluctuations. The emergence of superconductivity above 100 K, indeed on an energy scale comparable to room temperature, is a spectacular example of such robust macroscopic behaviour. Secondly, these compounds exhibit extreme sensitivity to external stimulation, a characteristic that descends from strongly nonlinear many-body dynamics and that borders chaotic phenomena. Indeed, a bewildering variety of phases appears to be stable under marginally different conditions, and can be accessed by weak perturbation. Finally, interactions are very fast, again due to the large energy scales at play, and emergent physics is already observable at the nanoscale.
Many conceptual hurdles stand in our way, largely because we have no effective way of predicting the behaviour of complex solids with accuracy. It is the purpose of this section of the proposal to make conceptual progress toward understanding of non-equilibrium processes after and under stimulation, a feat that requires frontier instrumentation and a new generation of light sources, as well as frontier theoretical techniques. Indeed, this collection of investigators is uniquely positioned to deliver in this area, establishing new techniques that are virtually unmatched worldwide.