Condensed Matter Seminar - "Spatiotemporal Engineering of Quantum Materials Far from Equilibrium"

Engineering quantum materials at the atomic scale — through epitaxial growth or mechanical exfoliation — has driven a remarkable era of discovery in 2D electronics and quantum physics. A new frontier is now emerging: using ultrafast light pulses to create transient phases of matter not just in space, but also in time. This direction calls for new materials synthesis strategies, characterization tools, and an integration between materials design and ultrafast optical control. I will present two recent examples from my group at the University of Chicago. First, we grow monolayer MnBi₂Te₄ by molecular beam epitaxy and show that photoexcitation drives it into an exciton condensate — a collective quantum state of bound electron-hole pairs. Tracked by time- and angle-resolved photoemission spectroscopy (trARPES), this condensate exhibits a 2D superfluid which persists up to 280 K. It can be continuously tuned between a fermionic (BCS-like) and bosonic (BEC-like) regime, offering a controllable platform for studying quantum many-body condensations in 2D materials. Second, we integrate topological insulator Bi₂Se₃ with a photonic crystal cavity to achieve spatiotemporal control over its electronic structure. The cavity confines the drive field to a 10×10 μm² footprint and extends the lifetime of light-dressed Floquet electronic states from ~300 fs to 2 ps, well beyond what free-space pulses allow. Our combined theoretical and experimental investigation shows that the spatiotemporal engineering of the Floquet states is robust against decoherence effects. This cavity-based approach offers a materials-level design strategy for programming and sustaining nonequilibrium topological phases, enabling photonics-driven nonequilibrium topological electronics.