The Effect of Copper Doping on Exciton Condensation in 1<i>T</i>-TiSe<sub>2</sub> Measured with meV-resolution EELS
ORAL
Abstract
The physical mechanism behind the charge density wave (CDW) in 1T-TiSe2 has been a subject of ongoing debate. Using momentum-resolved electron energy-loss spectroscopy (M-EELS), we observed a soft electronic collective mode in TiSe2 at the CDW transition temperature, TCDW = 185 K, demonstrating that the CDW results from exciton condensation. As TiSe2 is doped with copper to form CuxTiSe2, TCDW steadily decreases until a doping of x ~ 0.04, above which TCDW remains approximately constant and a superconducting dome emerges. At low doping values (x ≤ 0.02), the energy of the plasmon at q = 0 decreases as temperature decreases, but for high doping values (x = 0.07, 0.109) the plasmon energy increases as temperature decreases. We also find that for x ~ 0.004, the electronic mode softens partially, but not completely, at TCDW. For x > 0.01, the electronic mode no longer softens at TCDW, indicating that copper doping suppresses the exciton condensate in TiSe2 and that the CDW in CuxTiSe2 becomes a conventional, structural Peierls transition.
*This work was supported by the Gordon and Betty Moore Foundation's EPiQS Initiative through Grant GBMF-4542. Development of the M-EELS instrument was supported by the DOE Center for Emergent Superconductivity under award no. DE-AC02-98CH10886.
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Presenters
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Melinda Rak
- Univ of Illinois - Urbana
- Department of Physics and Materials Research Laboratory, University of Illinois