Correlated and Excited States in Moire Superlattices
Engineering quasiparticle properties and exploring emergent ferroelectric and magnetic orders in van der Waals heterostructures and moiré superlattices.
In his renowned 1959 lecture, “There is Plenty of Room at the Bottom,” Richard Feynman posed the question, “What could we do with layered structures with just the right layers?” Today, with the discovery of numerous van der Waals materials and the advancement of techniques to exfoliate and stack them, we have unprecedented opportunities to design and explore these layered heterostructures.
The Li group focuses on layered semiconductors and magnetic materials. In van der Waals bilayers, the conventional constraint of lattice matching at interfaces is removed. Instead, periodic variations in atomic alignment give rise to in-plane superlattices, known as moiré superlattices. The twist angle between layers serves as a powerful tool to tune material properties.
Our research explores innovative methods to engineer the properties and phases of quasiparticles, including excitons (bound electron-hole pairs), trions (excitons bound with an additional charge), and polarons. Additionally, we investigate the emergence of ferroelectric and magnetic orders within these moiré superlattices, uncovering new pathways to manipulate electronic and spin phenomena at the atomic scale.
New Dimensions to Optical Spectroscopy
Advancing spectroscopy tools to explore quantum coherence and enhance semiconductor metrology.
The Li group employs a diverse array of spectroscopy tools to investigate emerging quantum materials, continuously seeking to expand and refine these methods. While many research groups utilize Raman spectroscopy, we enhance its capabilities by performing measurements at low temperatures and under high magnetic fields. To probe low-energy excitations down to ~1 µeV (or 1 GHz), we leverage Brillouin scattering.
Additionally, we explore two-dimensional electronic coherent spectroscopy, extending beyond standard pump-probe and time-resolved MOKE techniques. By adding a new dimension to the spectra, this approach provides deeper insights into quantum coherent phenomena. Surprisingly, it has also shown great potential for advancing semiconductor chip metrology. Through these innovations, we aim to push the boundaries of material characterization and discovery.
Collective Excitations in Solids
How collective excitations, such as phonons and magnons, influence energy and spin transport in solids and drive novel phenomena through their interactions with electrons.
Atoms and spins in solids are not isolated; rather, their interactions give rise to collective excitations such as phonons and magnons. Our research focuses on understanding how these collective modes influence energy and spin transport, as well as the novel phenomena that emerge from their coupling with electrons. Recent studies from our group highlight examples like chiral phonons in CoTiO₃ and phonon renormalization in reconstructed moiré superlattices. Additionally, the Li group is proud to be part of a newly established Energy Frontier Research Center (EFRC) on magnonics, where we continue to explore cutting-edge advancements in this field. (https://ceemag.slac.stanford.edu/)
Quantum Transduction and Quantum Sensing
Exploring methods to transfer quantum information and harnessing the fragility of quantum systems for enhanced sensing.
Elaine began her graduate studies developing solid-state quantum gates. Now, her group is seeking new opportunities to contribute to the field of quantum information science. Their current research centers on enhancing quantum transduction between microwave and optical photons using nonlinear materials. Additionally, the group is investigating novel applications of solid-state spin defects to advance the performance of electronic and spintronic devices.
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