The Initial Process of Photoinduced Phase Transition in an Organic Electron-Lattice Correlated System using 10-fs Pulse

Transcription

1 The Initial Process of Photoinduced Phase Transition in an Organic Electron-Lattice Correlated System using 1-fs Pulse S. Koshihara, K. Onda, Y. Matsubara, T. Ishikawa, Y. Okimoto, T. Hiramatsu, G. Saito, Y. Nakano, H. Yamochi JST, CREST &, Tokyo Institute of Technology, Kyoto University Meijo University

2 What is a key for materials science, today. 1:How small part can interact with big one and regulate it? In case of photonic response, Photo-Induced Phase Transition (PIPT) 2:How artificially tune the property far from thermal effect? What kind of freedom in physical parameters can be tuned by light? Free from thermal effect utilizing photo-induced hidden phase is an attractive target.

3 Hidden phase (face) as an attractive target Lattice (Electronic, Magnetic) Relaxation New Lattice Structure and Electronic Order Transient state Ground State False Ground State Hidden Phase Nanometric How to probe the transient phase? Pump & Probe

4 Why electron-lattice strongly coupled system is an attractive candidate of PIPT? Localization of charges: Magnetism-Transport Localized charge coupled with lattice in Photo-excited state Dielectric-Transport-(Spin)(Common idea for multi-ferroics) Turn the face of materials by light T.Koda and Y.Tokura in Solid State Physcs Special Issue (1987) U/t Magnetic Mott Insulator with Spin Character Charge Order Metal Metallic V/t hν Dielectric

5 Following part: Three confessions by one Japanese Professor,,, 1: Shinya could not believe,,, 2: Shinya could not predict,,, 3: Shinya could not image,,,

6 Ultrafast melting of Ice of Charge in organic CT salt: Hidden phase of (EDO) 2 PF 6 Quasi-1D, 3/4-filled organic conductor with strong electron-lattice coupling 1mm 28 K R/R=1 means 1% change! Cooperative melting of electreon & lattice Ota, Yamochi, and Saito, J. Mater. Chem. 12, 26, (22) M. Chollet et al. Science, 37, 86 (25)

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8 Photo-induced Spectrum at 1 fs in Wide Energy Range (Finding of Hidden State (Hidden Order in Charge) Optical conductivity Theoretical Spectra new band (after photoexcitation) CT1 (before photoexcitation) CT1 CT3 CT2 CT2 CT3 (18 µm) (62 nm) (11)* charge order state K. Onda, et al. Phys. Rev. Lett. 11, 6743 (28)

9 In general Franck-Condon state photoexcitation Photoinduced Dynamics in CT Complexes charge melting or localization short-range order stabilization of molecular and crystal structure long-range order emergence of photo-induced phase fs 1 fs 1 fs 1 ps 1 ps 1 ps 1 ns (EDO-TTF) 2 PF 6 Pump:8 nm E stack new band CT1.1 ps Reflectivity HT phase (.5) LT phase (, +1) 1 ps CT3 CT2 R/R ps 3 ps Wavenumber (cm -1 ) Transient electronic spectra Time-resolved infrared ranging from IR to vis vibrational spectroscopy Phys. Rev. Lett. 28 J. Phys. Chem. C 212

10 Summary We studied the earliest process of photoinduced phase transition in a strongly correlated material (EDO-TTF) 2 PF 6. For this purpose, we obtained a 1 fs pulse from an amplified 12 fs pulse using a gas-filled hollow fiber. We found that it takes 4 fs from the Franck-Condon (FC) state to the photoinduced state. We also found that electronic coherence of the FC state lasts 24 fs accompanied with 128 cm -1 coherent phonon. The decoherence time does not depend on sample temperature. We succeeded in controlling emergence of photoinduced phase via electronic coherence using phase controlled double pulse.

11 Structural evidence of hidden charge-orbital coupled state in (Nd,Sr)MnO 3 thin film on STO(11) (Nd,Sr) MnO 6 hν T Ferromagnetic Metal High Temp. Phase Nd.5 Sr.5 MnO 3 /SrTiO 3 (11) (NSMO/STO(11)) CO-OO Insulator Low Temp. Phase

12 Changes in lattice constants seem to be consistent with simple I->M, but, but, but,,,, b, c (Å) Intensity (arb.) d out-of-plane / d in-plane d l / d s Delay time (ps) c b (1/4 9/4 ) T = 1 K Pump power:.8 mj /cm 2 3 X-ray pulse Energy: 15 kev FWHM: 1 ps T = 18 K T = 1 K Laser pulse Energy: 1.54 ev FWHM: 15 fs Nd.5 Sr.5 MnO 3 Intensity (arb.) SrTiO 3 (11) (e) (f) (4) LT (4) HT Detector 8 nm T = 18 K T = 1 K (4) LT Q (Å -1 ) 6.7

13 Comparison between temeprature and excitation power dependences of (4) and (4) reflections. Difference Intensity (arb. units) (4) L (4) H (4) L (a) without photo-irradiation Q (Å -1 ) 18 K (.5) 115 K 11 K 15 K (b) T = 1 K t d = 15 ps.8 mj / cm 2.6 mj / cm 2.4 mj / cm 2.2 mj / cm 2 Different from the simple expectation 6.7of CO,OO-Mteal PIPT 6.7and phase Separation. Q (Å -1 ) Homogeneous Hidden Phase appears by photo-excitation.

14 Hidden phase plays a common key role in strongly electron-lattice (Orbital) coupled systems (revealed by dynamical X-ray). Thermally induced M Photo-induced(CO-OO new phase) Ground State(CO-OO phase) Nature Materials 1 (211) 1

15 Next Importance key is the of hidden time-resolved state is widely SX and/or XAS expanded for orbital into transition and spin metal probe oxides Prof.S.Ishihara will give a talk. σ(ω) (1 3 Ω 1 cm -1 ) σ(ω) (1 3 Ω 1 cm -1 ) σ(ω) (1 3 Ω 1 cm -1 ) K 4 K ω c 3 K ω c ω c 3 K ps 4 K ps 1 3 K hω (ev) ps (a) Tb Gigantic fs photo-response (<4 K) in BaCo 2 O 5.5 (R=Sm, Gd and Tb) Hidden IS or HS magneto polaronic state? (b) Gd (c) Sm (Collaboration with Prof. T.Arima (Sample) and Prof. S.Ishihara (Theory) Groups (Tohoku Univ.)) Theory: Kanamori, Matsueda, Ishihara PRL 17, (211) Experiment: Y.Okimoto et al. PRB 84, 12112(R) (211)

16 Nucleation process and diffuse scattering (Prof. H.Cailleau discussed yesterday) Nucleation process molecular excitation Local excitation Domain formation Complete Dynamics similar to temperature dependence around 1 st order phase transition Diffuse scattering of TTF-CA at thermal equilibrium, associated with 1D correlation Guerin et al. Chemical Physics 299 (24)

17 Ski running will open next Blue Sky (Frontier Edge) for Materials Science Today Thank you for your attention! Tomorrow: Non-equilibrium materials science SX-HX dynamical measurements and combination with Lab. size experiments are essential tool for materials science tomorrow Until today: Static structural science Shift of paradigm maybe crash against tree in fog