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Condensed Matter Seminar: "Suppression of the exciton Bose condensate in TiSe2Cux by metallic screening"

Event Type
Physics - Condensed Matter
190 ESB
Feb 8, 2019   1:00 pm  
Peter Abbamonte, University of Illinois at Urbana-Champaign
Originating Calendar
Physics - Condensed Matter Seminar

The transition metal dichalcogenide semimetal 1T-TiSe2 exhibits a Bose condensate of excitons traditionally referred to as an “excitonic insulator” (though the material is not technically insulating) and highlighted as “excitonium” in the popular press. Using momentum-resolved electron energy-loss spectroscopy (M-EELS) experiments with meV energy resolution, we showed the experimental signature of this phase is a soft plasmon whose frequency falls to zero at the Bose condensation temperature [1]. Here, we analyze the stability of this phase against electron doping by performing M-EELS experiments in intercalated TiSe2Cux. We find that the excitonic state is quickly suppressed, the soft plasmon effect disappearing for x > 1% which coincides with the semimetal-metal transition (suitably defined). Surprisingly, we find that the periodic lattice distortion accompanying the excitonic transition persists even when the condensate has vanished, evolving into a trivial structural phase transition. Our study shows that exciton condensation is quickly destabilized when the Coulomb interaction is suppressed by metallic screening.


[1] A. Kogar, et al., Science 358, 1314 (2017)

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