Polariton laser in micropillar cavities

Transcription

1 Polariton laser in micropillar cavities D. Bajoni, E. Wertz, P. Senellart, I. Sagnes, S. Bouchoule, A. Miard, E. Semenova, A. Lemaître and J. Bloch Laboratoire de Photonique et de Nanostructures LPN/CNRS, Marcoussis, France Outline 2D GaAs cavities : polariton laser or photon laser? D polariton states in micropillars Polariton laser: D versus 2D OPO with D polariton modes Polariton electrical injection

2 Motivations Cavity polaritons : exciton photon mixed state Strong χ 3 non linearities : OPO (Savvidis PRL2, Stevenson PRL2, C. Diederich Nature2 ) > generation of correlated photon pairs 1.47 upper polariton photon exciton 1.47 lower polariton 4 C. Weisbuch et al., PRL 92 Bosonic statistic : macroscopic occupation of a quantum state BEC (J. Kasprzak Nature2, R. Balili Science27, C. W. Lai Nature27) Polariton laser: Low threshold source of coherent light (S. Christopoulos PRL27, D. Bajoni PRL28) 1 k // (cm )

3 Reports of Bosonic effects in semiconductor microcavities II VI (CdTe) : Non resonant excitation, Low temperature J. Kasprzak Nature2 GaN: Non resonant excitation, 3 K S. Christopoulos PRL27, G. Christmann APL 28 GaAs: Low temperature Non resonant excitation Trap in real space, R. Balili et al., Science 27 Resonant excitation, 2D Deng et al., Science 22, PRL 27 C. W. Lai,et al., Nature 27

4 Polariton relaxation under non resonant excitation cw non resonant Pump: high energy electron hole pairs Energy ) 1 + f ( Bosonic stimulation: Γ relaxation (f+1) f k // (µm ) 2 4 f >>1 : quantum degeneracy; coherence. But we need : Polariton lifetime >> Polariton relaxation time! Relaxation bottleneck

5 Polariton relaxation under non resonant excitation! Relaxation bottleneck, polariton polariton scattering to enhance polariton relaxation Tartakovskii, PRB 2, Senellart PRB 2! Exciton screening at high excitation density : strong coupling > weak coupling R. Houdré, PRB 199, R. Butté PRB 22 Screening of the strong coupling regime, electron hole plasma in the weak coupling regime Vertical Cavity Surface Emitting Laser We need high occupation factors for a moderate total exciton density

6 Large Rabi splitting GaAs microcavity: 2D Large number of quantum wells Total saturation density N x (one QW saturation density) Overcome relaxation bottleneck? 1 1 pairs 2 pairs Energy (m ev) 3 x 4 GaAs QW J. Bloch, APL (1998) HH 1 1 Ω Same structure as Yamamoto et al. Snoke et al. LH HH 1 mev 11 Position (mm)

7 Large Rabi splitting GaAs microcavity: 2D cw Emission at k// Energy at threshold Cavity mode

8 Large Rabi splitting GaAs microcavity: 2D cw Angle resolved photoluminescence δ 1. mev cavity m ode redshifted cavity m ode H H exciton 11 Lower polariton 1 P 2.2 P th P.3 P th..x 1 In plane wavevector (m )

9 Large Rabi splitting GaAs microcavity: 2D cw Angle resolved photoluminescence δ 1. mev cavity m ode redshifted cavity m ode H H exciton 11 Dispersion of a cavity mode Lower polariton 1 P 2.2 P th P.3 P th.. x 1 In plane wavevector (m ) Carrier induced refractive index renormalization Regular photon lasing! Too high carrier density

10 Large Rabi splitting GaAs microcavity: 2D Intensity distribution of the photon laser PL integrated Intensity (arb.u.) δ 1. mev P2.2 P th cw Similarities between photon laser and polariton condensate P.3 P th E E min (m ev) D. Bajoni et al., Phys. Rev. B 7, R213 (27)

11 Large Rabi splitting GaAs microcavity: 2D New generation of samples : higher finesse Q > 12 1 pairs 2 pairs 3 x 4 GaAs QW 2 pairs 3 pairs (mev) Energy 1 1 Energy at threshold Ω HH 1 mev Strong coupling?! Detuning Detuning(meV) (mev) 1 1

12 E Selective probe (emission or excitation) of the polariton states z θ k ( cm émission(θ ) θ k (4 cm 1) ) k ω /c sin(θ ) k

13 Large Rabi splitting GaAs microcavity: 2D New generation of samples : higher finesse m W 3 m W 2 m W m W m W 2 m W 1 m W 12 m W m W 9 mw 8 mw 7 mw mw mw 2 mw 1 mw. m W Energy (m ev) 13 Integrated Intensity (a.u.) Integrated Intensity (a.u.) δ +. mev Pump Power (mw )

14 Large Rabi splitting GaAs microcavity: 2D New generation of samples : higher finesse 1E8 δ +. mev P P th 1E E8 P 1E7 P th P Pth P Pth P.2 Pth x 1E8 P.2 P th 1E x 1x 2x 1 k // (m ) 3x 4x x

15 Large Rabi splitting GaAs microcavity: 2D New generation of samples : higher finesse δ +. mev 9 P P th P P th P,2 P th 8 7 T 4 K Occupancy (a.u.) 13 P Pth P Pth P.2 Pth x 2 4 E E min (mev) 1x 1x 2x 1 k // (m ) 3x 4x x

16 Large Rabi splitting GaAs microcavity: 2D New generation of samples : higher finesse Polariton lifetime >> relaxation time Build up of a large occupancy at k in the strong coupling regime Polariton laser (BEC?) in a GaAs 2D microcavity under NON RESONANT excitation Lateral confinement : D polariton states in the same sample Discussion of 2D versus D for polariton lasing

17 Photon modes in a micropillars Photons confined along z: kz pπ /Lc Photons confined along x and y: refractive index contrast between air and semiconductor kx pxπ /Lx ky pyπ /Ly Ly Lx Lc << Lx,Ly Discrete spectrum : px and py EPx, py size ( µm)... 2 c pπ p xπ p yπ + + n Lc Lx Ly 2

18 Exciton Photon coupling in micropillars Photon modes Exciton enveloppe function : p yπ y p xπ x E p x, p y ( x, y ) sin( ) sin( ) Lx Ly p yπ y p xπ x ψ px, p y ( x, y ) sin( ) sin( ) Lx Ly One to one coupling between exciton and photon modes (for lateral size > 2 µm) Ex px, py g g EC px, py G. Panzarini and L. C. Andreani, PRB, 1799 (1999) > Exciton photon mixed states Discrete polariton states

19 D polariton states in micropillars Fabrication : Electron beam lithography Reactive ion etching 2 pairs 2 2 µm 3 x 4 GaAs QW 3 pairs Cavity wedge > detuning 2 µm

20 D polariton states in micropillars Microphotoluminescence on a single micropillar PL Intensity (arb. units) 3 Discrete Circular pillar Polariton M odes diameter4 µm M1 M2 M3 T K M4 2 Q>12 µm Exciton Emission 1 1 Discrete spectrum of polariton modes

21 Another approach for D polaritons R. Idrissi Kaitouni, et al., PHYSICAL REVIEW B 74, 1311 (2) Ounsi El Daif et al., Applied Phys. Lett. 92, 819 (28)

22 Polariton laser in a micropillar Non resonant optical pumping δ mev PL Intensity (arb. units) 7 µm 2. mw 2 mw 1.2 mw.8 mw.3 mw.1 mw x4 x4 x4 x x Blueshift <. mev Strong coupling regime

23 Polariton laser in a micropillar Non resonant optical pumping PL Intensity (arb. units) 2. mw 2 mw 1.2 mw.8 mw.3 mw.1 mw coupling regime: 4 3 Strong Polariton laser 2 19 x4 x4 x4 x x2 199 µm 7 mw mw 3 mw mw 2. mw 4 PL Intensity (arb. units) δ mev Weak coupling regime: Photon laser Onset of photon lasing at higher excitation power D. Bajoni et al., Phys. Rev. Lett., 4741 (28)

24 Em ission energy (mev) Polariton laser Photon laser µm Measured occupancy Emission integrated intensity (arb. u.) Polariton laser in a micropillar % of the injected electron hole pairs Polariton laser 199 More than polaritons in the same quantum state 198 Photon laser Excitation power (mw ) D. Bajoni et al., Phys. Rev. Lett., 4741 (28) Estimated exciton density : cm 2/QW

25 Em ission energy (mev) Polariton laser Photon laser Photon laser Photon laser : non interacting bosons Polariton laser 199 µm Measured occupancy Emission integrated intensity (arb. u.) Polariton laser in a micropillar Excitation power (mw ) Polariton laser : self interaction responsible for the observed blueshift

26 2 Threshold (x W cm ) Polariton laser in a micropillar Photon laser 1.1 Polariton laser Pillar size (µm ) times lower threshold!!!

27 Polariton laser in a micropillar PL PL intensity intensity (arb. (arb. u.) u.) Centered Centered.8 mw mw.8.7 mw.7 mw. mw mw..2 mw mw.2 1x 1x 7x 7x Edge 4x 3x 2x 1x Diameter µm mw mw mw mw edge excitation: stimulation toward M2, M3 x. 3x 3x Integrated Integrated PL PL intensity intensity xx x Energy (m ev) Energy (m ev) 8 8 M ode1 Mode1 M ode2 Mode2 M ode3 7 7 Mode power (m W ) Excitation Excitation power (m W ) 8 7 Polariton Lasing with mode competition

28 Polariton laser in a micropillar: mode competition Large micropilllar Smaller micropilllar 4 µm 4 3 4x 3x 2x 1x 2 mw 1 mw Power (µw ) Multimode, fragmentation Energy (ev) 1 mw 2 mw x 3x 1 mw Intensity (arb. u.) 7 x Intensity (arb. u.) x 8 Intensity (arb.u.) Integrated intensity (arb. u.) µm 2x 1x. mw Power (µw) Lasing on the ground state. mw 1 mw

29 Mode competition: 2D versus D II VI 2D cavity Laser without power fluctuation: multimode polariton lasing Reduced dimensionality : A unique system for quantum degeneracy in a well controled quantum state

30 OPO with D polaritons Parametric scattering between discrete D polariton modes PL Intensity (arb. Units) Energy conservation: Ei Ep Ep Es Square pillar 4 µm side T4K 1 s 14 Symmetry conservation: P 2 14 i 14 E G. Dasbach et al., PRB 4 R2139 (21) * Pump * 4 ( r )E Pump ' ( r ) Esignal ( r ) Eidler ( r )d r

31 OPO with D polaritons E Px, py Energy conservation: Ei Ep Ep Es c n 2 pπ p xπ p yπ + + Lc Lx Ly (2,2) E + 8 Econf (2,1),(1,2) E + Econf (1,1) E + 2 Econf 2 2 Spectral Equidistance

32 OPO with D polaritons (2,2) Energy conservation: Ei Ep Ep Es (2,1) + (1,2) Symmetry conservation: * 2 * E ( r ) E ( r ) E ( r ) E ( r Pump Pump ' signal idler )d r (1,1)

33 OPO in micropillars 3. µm square T K Intensity (arb. u.) M1 M2 M2 M Energy (m ev) x 7. x M1 Pump M3 P P P P P P 1 m W 9 m W 7 m W 1 m W 2 m W mw. 194 D. Bajoni et al., Applied Phys. Lett. 9, 17 (27)

34 OPO in micropillars 3. µm square T K 7 4 M2 M1 M3 Intensity (arb. u.) Integrated Intensity (a. u.) 1.x 7.x M1 Pump M3 P P P P P P 1 m W 9 m W 7 m W 1 m W 2 m W mw Pum p Power (mw ) First observation of parametric oscillations on a single micropillar 12

35 OPO with microcavity polaritons Idler Signal pump idler 9 signal Pump : 17 Idler at very large angle and weakly coupled to the external field P.G. Savvidis et al. PRL (2) R. M. Stevenson et al. PRL 8 38 (2) Micropillars Multiple cavities (collaboration J. Tignon and A. Bramati) Same intensity for signal and idler

36 Polariton electrical injection D. Bajoni et al., Phys. Rev. B 77, (28)

37 Polariton electrical injection Log(EL intensity) Log(EL intensity) (arb. units) (arb. units) T TKK I1 I1m maa Log(EL intensity) Log(EL intensity) (arb. units) (arb. units) T TKK I7 I7mmAA Cavity mode Angle Angle(degrees) (degrees) Bleaching of the strong coupling Angle Angle(degrees) (degrees)

38 Polariton electrical injection T K Three groups : A. Khalifa et al., Appl. Phys. Lett. 92, 17 (28) T K D. Bajoni et al., Phys. Rev. B 77, (28) T K S. I. Tsintzos et al., Nature (28) T 23 K Further optimisation : polariton laser under electrical injection

39 Summary GaAs cavities : High finesse + Many QWs 7 PL Intensity (arb. units) Polariton lasing (BEC?) under non resonant excitation in 2D and in D x4 x4 x4 x x2 Multimode lasing in 2D and pillars > µm 2. m W 2 mw 1.2 m W.8 m W.3 m W.1 m W Energy (m ev) Small micropillars (< µm): quantum degeneracy of a well controlled polariton state OPO with discrete polariton states.x Lo g(el intensity) (arb. u nits) m W 9 m W 7 m W 1 m W 2 m W mw T K I1 m A T K I7 m A RTN Clermont II Electrical injection of polaritons L og(el intensity) (arb. u nits) x Intensity (arb. u.) 1484 P P P P P P Angle (degrees) Angle (degrees) 2