ULTRAFAST CONTROL OF POLARITON STIMULATED SCATTERING IN SEMICONDUCTOR MICROCAVITIES Cornelius Grossmann1 G. Christmann, C. Coulson and J.J. Baumberg Nanophotonics Centre, Cavendish Laboratory, University of Cambridge N. T. Pelekanos, Z. Hatzopoulos, S. I. Tsinzos and P. G. Savvidis Department of Materials Science and Technology, University of Crete PLMCN10, Cuernavaca, Mexico 15 th april 2010

Cornelius Grossmann2 Strong coupling regime C. Weisbuch et al., PRL (1992) Strong-coupling regime: reabsorption time < cavity lifetime semiconductor microcavity coupling between a electronic transition and a Fabry-Perot mode

Cornelius Grossmann3 Parametric scattering process parametric conversion: probe stimulation at k s = 0 energy and momentum conservation! Savvidis et. al., PRL (2000) coherent χ (3) process in semiconductor microcavities χ (3) -nonlinearity: exciton-exciton interaction probe gain highly dependent on pump-LPB resonance 2k p = k s +k i 2E(k p )= E(k s )+E(k i ) χ (3)

Cornelius Grossmann4 Under external bias Polariton light emitting diode D. Tsintzos et al., Nature (2008) Quantum confined Stark effect conduction band valence band GaAs InGaAs GaAs Growth axis Applied bias consequences change of energy of excitonic transition separation of electron and hole wavefunctions

Cornelius Grossmann5 Electrically pumped polariton devices Optical bistability in GaAs-based Polariton LED Bajoni et. al., PRL (2008) Electroluminescence up to RT Tsintzos et. al., APL (2009) Khalifa et. al., APL (2008) Bajoni et. al., PRB (2008)

Cornelius Grossmann6 Motivation for the bias The parametric scattering process is due to exciton-exciton interaction through χ (3) The excitons are aligned Tailoring of the exciton-exciton interaction Consequences on the parametric amplification in microcavities? Growth axis

Cornelius Grossmann7 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 Grossmann8 Voltage scan: Stark effect Stark tuning of the excitons Rabi splitting of 6 meV Reflection spectra

Cornelius Grossmann9 Voltage scan: pump-probe 2 effects: gain-loss at negative bias, dispersion-less gain-loss at negative bias: detuning of pump and LPB gain dip at positive bias

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

Cornelius Grossmann11 sharp gain dip 100 mV > 90% sharp dip additional photocurrent at this bias

Cornelius Grossmann12 Tunneling 2 competing processes Rabi-oscillations: redistribution of e - /h-pairs over QWs carrier tunneling: separation of e - /h-pairs LO-phonon induced tunneling 100 fs carrier escape 180 ns, 230 fs extra e - population creates extra scattering OPO gain sensitive to broadening C. Ciuti et al. PRB 62 R4825 (2000)

Cornelius Grossmann13 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 Grossmann14 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/F EU Clermont 4