My research focuses on studying dynamic collective phenomena in quantum materials, including electron self-organization, such as charge and spin wave or stripe order, topological phases, strange metals, exciton condensation and superconductivity. We use different X-ray and electron scattering and spectroscopy techniques to characterize elementary collective excitations.
In 2017, we discovered a new form of matter called excitonium, in the material titanium diselenide, that has perplexed scientists since it was first theorized in 1968 by Bert Halperin and Maurice Rice. Excitonium is a bosonic condensate — it exhibits macroscopic quantum phenomena, much like superconductivity or superfluidity. It is made up of quasiparticles called excitons, which are formed through the pairing of an electron that has escaped from an atom and the hole it left behind. The discovery was made possible by a novel scientific instrument called momentum-resolved electron energy-loss spectroscopy (M-EELS).
M-EELS is more sensitive to valence band excitations than inelastic x-ray or neutron scattering techniques. We are interested in using this tool to explore several key problems in quantum materials, such as determining whether fluctuations of charge-ordered states play a key role in high-temperature superconductivity of cuprates, study metals that exhibit strange-metal behavior and look for evidence of axions in topological insulators.
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Emergent Phenomena in Quantum Systems
University of Illinois at Urbana-Champaign, Department of Physics