Grant: Discovery Grants Program - Individual

Two-dimensional materials - atomically thin crystal layers - and the layer-by-layer stacks that are frequently made from them, have emerged as one of the most fruitful platforms from which to engineer exotic electronic functionality. Such stacks of 2D materials are held together just by van der Waals (vdW) forces, the same forces that give geckos the ability to climb smooth vertical surfaces. Due to the multiplicity of possible stacking arrangements, so-called vdW stacks can host an enormous range of electronic behaviours. Even stacks made exclusively from the 2D carbon material graphene, with protective layers on either side, can exhibit superconductivity or ferromagnetism, among other phenomena, all accessible in a single device just by tuning a gate voltage. Almost all experimental investigations of vdW heterostructures are made using electrical resistance measurements, reflecting the established power of that technique to probe samples even down to the single-molecule scale. As convenient as conductance measurements are, at a fundamental level they record only one aspect of a sample's electronic state - how carriers scatter as they move through the sample - but are blind to other characteristics that are often crucial to understanding its underlying nature. Thermodynamic probes are a powerful complement to conductance measurements, enabling (for example) measurements of entropy, thermal conductivity or magnetization. Such probes are, however, extremely difficult to implement in nanoscale systems and, for that reason, are much less often attempted when investigating vdW stacks. The present proposal offers a fresh approach to measuring thermodynamic properties in 2D materials, bringing together two areas that are, for now, independent strengths of my research group: the measurement of strongly correlated or topological states in 2D materials such as graphene, and the use of thermodynamic probes for studying quantum devices built from conventional semiconductors. We propose a hybrid approach, exploiting GaAs circuit elements already developed as thermometers and chemical-potential sensors, and integrating them with a vdW stack. The result will be an order-of-magnitude improvement in the power of thermal measurements to probe electronic states in 2D materials, pushing open a new window into their behaviours. This effort joins us with some of the most vibrant experimental and theoretical communities in condensed matter physics, offering a superb training program for our HQP with direct connections to leading scientists at elite research institutions across the world. The impact of discoveries emerging from 2D material devices may be as broad as the types of electronic states they host: from a versatile testbed for exploring quantum many-body physics (which is likely to be the key to understanding phenomena such as high-temperature superconductivity), to establishing new avenues to quantum technologies based on topological states.