Berlin 2008 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 39: Ultra fast phenomena

HL 39.5: Vortrag

Donnerstag, 28. Februar 2008, 12:15–12:30, ER 270

THz Lyman spectroscopy and coherent THz control of dark excitons in Cu₂O — •Silvan Leinß¹, Tobias Kampfrath², Konrad v. Volkmann², Martin Wolf², Dietmar Fröhlich³, Alfred Leitenstorfer¹, and Rupert Huber¹ — ¹Department of Physics, University of Konstanz, 78464 Konstanz — ²Department of Physics, Free University Berlin, Arnimallee 14, 14195 Berlin — ³Department of Physics, University of Dortmund, 44221 Dortmund

We employ ultrabroadband THz pulses to resonantly couple to the internal exchange-split 1s-2p Lyman doublet of yellow excitons in Cu₂0 (T_L = 4 K). A line shape analysis provides absolute values of density and temperature of the optically dark exciton gas forming after two-photon photogeneration of unbound electron-hole pairs. At a delay time of 100 ps, 1s-para states are observed with a density of 2 × 10¹⁶ cm⁻³ and a temperature of 12 K. Intense THz transients with peak electric fields of 0.5 MV/cm allow us to coherently control the internal quantum state of this ensemble via a partial intra-excitonic Rabi flop. Up to 70% of the quasiparticles are promoted from the 1s into the 2p state. Electro-optic sampling directly monitors the Larmor precession of the Bloch vector in real time. The results suggest a promising new route for preparing ultracold and dense exciton gases.