ULTRAFAST CONTROL OF POLARITON STIMULATED SCATTERING IN SEMICONDUCTOR MICROCAVITIES

1. Cornelius Grossmann ULTRAFAST CONTROL OF POLARITON STIMULATED SCATTERING IN SEMICONDUCTOR MICROCAVITIES G. Christmann, C. Coulson and J.J. Baumberg Nanophotonics Centre, Cavendish Laboratory, University of Cambridge N. T. Pelekanos, Z. Hatzopoulos, S. I. Tsinzosand P. G. Savvidis Department of Materials Science and Technology, University of Crete PLMCN10, Cuernavaca, Mexico Cornelius Grossmann

2. Strong coupling regime Strong-coupling regime: reabsorption time < cavity lifetime semiconductor microcavity coupling between a electronic transition and a Fabry-Perot mode C. Weisbuch et al., PRL 69 3314 (1992) Cornelius Grossmann

3. Parametric scattering process • parametric conversion: • probe stimulation at ks= 0 • energy and momentum conservation! χ(3) 2kp= ks+ki 2E(kp)= E(ks)+E(ki) • coherent χ(3) process in semiconductor microcavities • χ(3)-nonlinearity: exciton-exciton interaction • probe gain highly dependent on pump-LPB resonance Cornelius Grossmann Savvidis et. al., PRL 84 1547 (2000)

4. Under external bias Polariton light emitting diode Quantum confined Stark effect conduction band Applied bias valence band D. Tsintzos et al., Nature 453 372 (2008) GaAsInGaAsGaAs Growth axis consequences change of energy of excitonic transition separation of electron and hole wavefunctions Cornelius Grossmann

5. Electrically pumped polariton devices Electroluminescence up to RT Optical bistability in GaAs-based Polariton LED Bajoni et. al., PRL 101 266402 (2008) Tsintzos et. al., APL 94 071109 (2009) Khalifa et. al., APL 92 061107 (2008) Bajoni et. al., PRB 77 113303 (2008) Cornelius Grossmann

6. Motivation for the bias The parametric scattering process is due to exciton-exciton interaction through χ(3) Growth axis The excitons are aligned Tailoring of the exciton-exciton interaction Consequences on the parametric amplification in microcavities? Cornelius Grossmann

7. Experimental setup • fs mode-locked Ti:Sa laser system • pump spectrally filtered and • broadband probe pulse • pump at the magic-angle • probe at k||= 0 • recording of • pump reflected spectrum • incident probe • reflected probe • in parallel: electrical measurements Cornelius Grossmann

8. Voltage scan: Stark effect Reflection spectra Stark tuning of the excitons Rabi splitting of 6 meV Cornelius Grossmann

9. Voltage scan: pump-probe • 2 effects: • gain-loss at negative bias, dispersion-less • gain dip at positive bias gain-loss at negative bias: detuning of pump and LPB Cornelius Grossmann

10. Negative bias: gain loss • unbiased resonance of pump and LPB: efficient parametric amplification  efficient carrier injection • biased Stark-tuning of excitons: pump out of resonance with LPB  inefficient carrier injection No screening of external electric field! Cornelius Grossmann

11. sharp gain dip sharp dip 100 mV > 90% additional photocurrent at this bias Cornelius Grossmann

12. Tunneling • 2 competing processes • Rabi-oscillations: redistribution of • e-/h-pairs over QWs • carrier tunneling: separation of • e-/h-pairs • LO-phonon induced tunneling100 fs • carrier escape 180 ns, 230 fs • extra e- population creates extra scattering • OPO gain sensitive to broadening C. Ciutiet al. PRB 62 R4825 (2000) Cornelius Grossmann

13. Summary & outlook electrical control of the parametric gain sharp and dramatic gain modulation Stark tuning with “small” electrical fields: ultrafast response expected Potential realization of Thz modulators? Cornelius Grossmann

14. Support and funding • Pavlos G. Savvidis et. al.: Polariton LED sample • Gabriel Christmann, Chris Coulson and Jeremy Baumberg: spectroscopy & simulation • Funding: • UK EPSRC EP/C511786/1, EP/F011393 • EU Clermont 4 Cornelius Grossmann