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Physics Colloquium Series: Professor Peter Abbamonte
(Physics Lecture Series) University of Illinois, Department of Physics
“Bose condensation of excitons in a transition metal dichalcogenide”
Bose condensation has shaped our understanding of macroscopic quantum phenomena, having been realized in superconductors, atomic gases, and liquid helium. Excitons are bosons that have been predicted to condense into either a superfluid or an insulating electronic crystal. But definitive evidence for a thermodynamically stable exciton condensate has never been achieved.
In this talk I will describe our use of momentum-resolved electron energy-loss spectroscopy to demonstrate the existence of exciton
condensation in the transition metal dichalcogenide semimetal, 1T-TiSe2. Its experimental signature is a “soft plasmon” that disperses to zero energy at the Bose condensation temperature. Our study demonstrates the existence of a new form of matter, “excitonium,” which was postulated to exist in the 1960’s but not observed until now.