What did the 2012 Early Career Award Allow You to Do
Semiconductors are materials which have an electrical conductivity ranging between conductors and insulators. They can be pure elements or compounds. Semiconductors are key to modern science and technology. This is because their electrical conductivity can be controlled using a variety of external tuning knobs.
The Early Career Award has enabled me to establish a range of fabrication and optical measurement tools. With these tools, we can create, probe, and understand the physics arising from the behavior of large numbers of electrons in atomically thin semiconductors.
The ability to isolate graphene taught us how to obtain single atomic layer, or monolayer, semiconductors. The most famous of these are of a type called transition metal dichalcogenides (TMDs). We, along with other researchers, have found that these monolayer semiconductors are distinct from normal bulk semiconductors due to their unique physical properties.
Our early efforts discovered two TMDs - MoSe2 and WSe2 - as two clean semiconductors with exceptional optical properties, meaning laser light can excite electrons in these materials. These electrons bind strongly with the positively charged "bubbles" - or holes - left behind, forming excitons. These dominate the optical response, and the momentum – or "valley" – of the exciton is linked to the optical polarization. This property allows scientists to use polarized light to create a quantum superposition of the valley states. Electric fields can be used to control excitons. Therefore, it is also possible to create electro-optical devices in these systems. One example is 2D light emitting diodes (LEDs), used for lighting.
We also developed 2D multilayer structures, made by stacking two different monolayer semiconductors. These devices are a powerful platform to study the emergent effects of many interacting particles (such as excitons, electrons, and holes).
We are working on emergent properties in these systems, including creating and understanding topological and strongly correlated physics. One exciting example is our recent discovery of ferromagnetism – or ordering of spins – induced by the excitons. The established research program has also enabled us to carry out a series of experiments that have created the fast-growing field of 2D magnets.
These systems provide a platform to study the most fascinating problems in physics – magnetism and topology. They also offer promising ways to realize energy efficient information, data storage, and computing technologies.
We continue to explore this field, focusing on understanding and developing new ways to control the coupling between spins, charges, and the underlying lattice of the system.