Transcript of Exciton interstate dynamics in photoexcited quantum wells manipulated by strong narrow-band THz...
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- Exciton interstate dynamics in photoexcited quantum wells
manipulated by strong narrow-band THz pulses Sangam Chatterjee
TAC-LSUM, 6.10.2013
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- Acknowledgements Experiment: Nils Rosemann, Alexey Chernikov,
Benjamin Ewers, Martin Koch Martin Teich, Sybine Zybell, Harald
Schneider, Manfred Helm (Helmholtz-Zentrum Dresden-Rossendorf)
William D. Rice, Junichiro Kono (Rice University) Theory: Andrea
Klettke, Lukas Schneebeli, Mackillo Kira, Stephan W. Koch Samples:
Galina Khitrova, Hyatt M. Gibbs (The University of Arizona) Stephan
Schartner, Gottfried Strasser (TU Wien) 2
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- Outline: Introduction: Excitons, Autler-Townes Effect &
Ionization 1s-2p Interstate Coherence and 2s-2p Quantum Beats
Population Control: Rabi-Flopping of 1s-2s Excitons Conclusions
& Outlook 3
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- Introduction: From Atoms to Solids to Excitons crystal bands 4
3 2 n=1 energy atom levelsatom-like dispersion exciton + -
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- 5 Time-Resolved Spectroscopy on Semiconductors Different
physical phenomena different time scales Optical Excitation
Polarization and dephasing Carier injection and cooling Formation
many-body excitations time 0
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- Introduction: Optical vs. THz Spectroscopy 6 EgEg Valence Band
p-type k E THz Photon Conduction Band s-type
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- Detection of Excitons: Optical pump + THz probe 7
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- THz Absorption Identifies Excitons and Plasma 8
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- Polarization Manipulation: Weak Optical + Strong THz Excitation
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- Polarization Manipulation: Weak Optical + Strong THz Excitation
(II) M. Wagner et al., Phys. Rev. Lett. 105, 167401 (2010) B. Ewers
et al, Phys. Rev. B 85, 075307 (2012)
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- Reminder: Driven 2-Level-System (I) Linear absorption of a 2LS:
E 0
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- Reminder : Driven 2-Level-System (II) Rabi-Splitting, Mollow
triplet E 0
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- Reminder : Autler-Townes Effect Rabi-Splitting, Autler-Townes
effect, E 0
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- Messages & Questions (I) E 0 E 0
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- Inter-level Coherences: Optical-Pump THz-Four-Wave Mixing 15 to
Ge:Ga Detector
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- Optical-Pump THz-Probe 1s exciton lifetime: ~330ps (THz)
Similar to 1s TRPL lifetime 16
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- Optical-Pump THz-Pump THz-Probe 1s exciton lifetime: ~330ps
(THz) Similar to 1s TRPL lifetime Opt. Pump THz Pump THz Probe
Interference pattern Shelving at later times 17
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- Optical-Pump THz-Pump THz-Probe 1s exciton lifetime: ~330ps
(THz) Similar to 1s TRPL lifetime Opt. Pump THz Pump THz Probe
Interference pattern Shelving at later times 18
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- Optical-Pump THz-Pump THz-Probe 1s exciton lifetime: ~330ps
(THz) Similar to 1s TRPL lifetime Opt. Pump THz Pump THz Probe
Interference pattern Shelving at later times Oscillation period:
118m 19
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- Optical-Pump THz-Pump THz-Probe 20 1s exciton lifetime: ~330ps
(THz) Similar to 1s TRPL lifetime Opt. Pump THz Pump THz Probe
Interference pattern Shelving at later times Oscillation period:
118m
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- Optical-Pump THz-Four-Wave Mixing 21 Decay ~50ps Similar to 2s
TRPL lifetime Mechanism: acoustic phonons Overlayed by slow
oscillation Period: 100ps Energy: 40eV Quantum beat of 2s-2p
Splitting confirmed independently by magneto-PL
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- Optical-Pump THz-Four-Wave Mixing 22 Decay ~50ps Similar to 2s
TRPL lifetime Mechanism: acoustic phonons Overlayed by slow
oscillation Period: 100ps Energy: 40eV Quantum beat of 2s-2p
Splitting confirmed independently by magneto-PL
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- Optical-Pump THz-Four-Wave Mixing 23 Decay ~50ps Similar to 2s
TRPL lifetime Mechanism: acoustic phonons Overlayed by slow
oscillation Period: 100ps Energy: 40eV Quantum beat of 2s-2p
Splitting confirmed independently by magneto-PL
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- Optical-Pump THz-Four-Wave Mixing 24 Decay ~50ps Similar to 2s
TRPL lifetime Mechanism: acoustic phonons Overlayed by slow
oscillation Period: 100ps Energy: 40eV Quantum beat of 2s-2p
Splitting confirmed independently by magneto-PL
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- Next: Population Manipulation Optical & THz Pumping, TRPL
Detection 25 Resonant with 1s Resonant with 1s 2p FEL
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- Population Control: Optical & THz Pumping, TRPL Detection
26 THz OFFTHz ON Energy E-E 1s (meV) Time (ps) 0 1
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- Population Control: Optical & THz Pumping, TRPL Detection
27
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- Population Control: Optical & THz Pumping, TRPL Detection
28
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- Theory: Coulomb-Induced Symmetry Breaking 2-particle exciton
correlation Exciton dynamics Conservation law Diffusive scattering
Coulomb scattering breaks THz-dipole symmetry 29
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- Messages & Questions (II) Excitonic Autler-Townes Effect
Multi-THz-Photon Ionization Coulomb-Mediated Coupling of 2s and 2p
Exitons Shelving of Excitons (no carrier loss)
THz-Power-dependence? 30
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- Back to Population Manipulation: Optical & THz Pumping,
TRPL Detection 31 Resonant with 1s Resonant with 1s 2p FEL
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- Back to Population Manipulation: Optical & THz Pumping,
TRPL Detection 32 Resonant with 2s Resonant with 1s 2p FEL
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- 33 Resonant 2s Optical Excitation
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- 34 FEL offFEL on Energy (meV)
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- THz-Power-Dependence Resonant 2s pumping: Nonmonotoneous PL
strength Density-dependent period (Coulomb-induced change of
dipole-matrix element) Resonant 1s pumping: Similar behaviour Less
pronounced due to unaffected 1s emission 35
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- Conclusions & Outlook Manipulation of exciton populations
using strong THz pulses Unexpected strong 2s photoluminescence
after 1s-2p excitation Evidence of Coulomb-mediated coupling of 2s
and 2p levels Shelfving of excitons in states with large angular
momenta Phys. Rev. Lett. 110, 137404 (2013) 1s-2p transition
predominantly homogeneously broadened 1s-2p coherence times several
100s of ps Observation of quantum beat corresponding to 2s-2p
separation Secondary emission shows Rabi-Flopping between 1s and 2s
Outlook: Coherent State Control, THz Gain... 36
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- Messages & Questions (III) 37
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- 38 2s pump 1s pump FEL offFEL on
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- Resonant 1s Optical Excitation 39 FEL offFEL on Energy
(meV)
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- Nonresonant Excitatation, Long Time Delay 40
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- THz-Power-Dependence: 2s Optical Pumping 41
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- THz-Power-Dependence 2s optical pumping1s optical pumping
42
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- Optical-Pump THz-Four-Wave Mixing 43 t THz-THz (ps) 200 0 -100
100 THz Intensity (arb. Units)
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- Optical-Pump THz-Four-Wave Mixing 44 t THz-THz (ps) 200 0 -100
100 THz Intensity (arb. Units)
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- Outline: Introduction: Excitons Interband Polarization Control:
Excitonic Autler-Townes Effect and THz-Field ionization Population
Control: Coupling of 1s-2s excitons Excitation: Optical-Pump
THz-Pump Detection: Time-Resolved Photoluminescence 1s-2p
Interstate Coherence and 2s-2p Quantum Beats Opt.-Pump - THz-Probe
/ Opt.-Pump - THz-Pump - THz-Probe Degenerate Four-Wave Mixing
Conclusions & Outlook 45
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- Show 1s-2s- coupling Explain showing theory Wonder about
coherence of this transition Shown FWM FWM lifetime roughly equal
to 2s PL lifetim 1s-2p homogeneously broadened (PP-lifetime ~ FWM
lifetime Mechanism for both is AC phonon coupling Beat show
signatures of 2s-2p by beating Energy separation independently
veryfied by magnetp-PL bhattacharya et al. In press If coherent can
we see rabi oscillations Yes, we can in P Intensity of 1s and 2s pl
varies with changing THz fluence 46
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- Experimental Setup Source: 1kHz Ti.Sapphire Amplifier 120fs,
1mJ, 800nm pulses Coaxial geometry for NIR & THz
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- Strong Single-Cycle THz-Pulses Sample: Narrow-Linewidth MQW THz
pulse 1s hh exciton @ 4K 30x Ga 0.96 In 0.04 As, 8nm
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- Experiment: THz-Induced Bleaching
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- Experiment: Time Evolution
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- Experiment: Density Dependence
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- Experiment Theory Comparison ExperimentTheory
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- Weak Optical + Strong THz Excitation (IV) B. Ewers et al, Phys.
Rev. B 85, 075307 (2012)
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- Introduction: THz Experiments in Semiconductors 54
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