TY - JOUR
T1 - Dynamics of incoherent exciton formation in C u2 O
T2 - Time- And angle-resolved photoemission spectroscopy
AU - Tanimura, H.
AU - Tanimura, K.
AU - Van Loosdrecht, P. H.M.
N1 - Funding Information:
We thank K. Nasu, J. Kanasaki, and J. Güdde for valuable discussions. This work was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI Grant No. 24000006.
PY - 2019/9/30
Y1 - 2019/9/30
N2 - We study the dynamics of incoherent exciton formation under interband photoexcitation in Cu2O using time-and angle-resolved photoemission spectroscopy at 90 K. Hot electrons injected by allowed optical transitions with 3.40-eV photons show ultrafast relaxation to the conduction-band minimum (CBM), surviving up to 500 fs after excitation. Whereas hot-electron states with high excess energy show a rapid population decay of ∼25 fs, an abrupt increase to 130 fs is observed for states with excess energies of 0.15 eV. This latter is interpreted in terms of phonon bottleneck dynamics characteristic of longitudinal-optical phonon mediated energy relaxation. Excitons, having a small binding energy of 60 meV, are formed below the CBM quasi-instantaneously and subsequently relax to the 1S-exciton state of the yellow series within 1.5 ps. We find that, together with possible plasma screening for electron-hole interaction, the cooling of exciton center-of-mass motion plays an important role in the exciton relaxation dynamics. The characteristic features of exciton photoionization process are critically discussed based on the detailed analysis of angle-resolved photoemission results for the 1S excitons formed 1.5 ps after excitation.
AB - We study the dynamics of incoherent exciton formation under interband photoexcitation in Cu2O using time-and angle-resolved photoemission spectroscopy at 90 K. Hot electrons injected by allowed optical transitions with 3.40-eV photons show ultrafast relaxation to the conduction-band minimum (CBM), surviving up to 500 fs after excitation. Whereas hot-electron states with high excess energy show a rapid population decay of ∼25 fs, an abrupt increase to 130 fs is observed for states with excess energies of 0.15 eV. This latter is interpreted in terms of phonon bottleneck dynamics characteristic of longitudinal-optical phonon mediated energy relaxation. Excitons, having a small binding energy of 60 meV, are formed below the CBM quasi-instantaneously and subsequently relax to the 1S-exciton state of the yellow series within 1.5 ps. We find that, together with possible plasma screening for electron-hole interaction, the cooling of exciton center-of-mass motion plays an important role in the exciton relaxation dynamics. The characteristic features of exciton photoionization process are critically discussed based on the detailed analysis of angle-resolved photoemission results for the 1S excitons formed 1.5 ps after excitation.
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U2 - 10.1103/PhysRevB.100.115204
DO - 10.1103/PhysRevB.100.115204
M3 - Article
AN - SCOPUS:85073195116
VL - 100
JO - Physical Review B
JF - Physical Review B
SN - 2469-9950
IS - 11
M1 - 115204
ER -