Presentation Information
[9p-E206-3]Visualizing the exciton formation from free carriers in monolayer WSe2 in energy and momentum spaces
〇(P)Takumi Fukuda1, Xing Zhu1, Enrico Perfetto2,3, Jacques Hawecker1, Harley Suchiang1, Joanna Nadolna1,6, Nanami Tomoda1, Suji Park4, Houk Jang4, Kenji Watanabe5, Takashi Taniguchi5, Michael Man1, Julien Madeo1, Keshav Dani1 (1.OIST, 2.Univ. Rome, 3.INFN, 4.BNL, 5.NIMS, 6.Univ. Gdansk)
Keywords:
TR-ARPES,free carrier,exciton
We performed time- and angle-resolved photoemission spectroscopy (TR-ARPES) on a monolayer (1L-) WSe2 using a time-of-flight momentum microscope (ToF-MM) to visualize the energy- and momentum-resolved dynamics during the formation of bound excitons from unbound states. Our TR-ARPES data reveal that conduction-band populations (free carriers) emerge at energies more than 2 eV above the valence-band maximum at both the K and Q points immediately after photoexcitation (0.0 ps). Within 1.0 ps, a significant fraction of these carriers evolves into exciton states at ~1.8 eV. The delayed formation (~300 fs) of excitons from free carriers is attributed to be a phonon bottleneck that slows the scattering rate from conduction bands into excitonic states. In this talk, we will further discuss the timescale and microscopic mechanism of the scattering processes governing the transition from unbound free carriers to bound excitons.