SEARCH FOR PHOTO-INDUCED PHASE TRANSITON WITH ULTRAFAST RESPONSE BASED ON ELECTRONIC- STRUCTURAL COUPLED PROBES

Transcription

1 SEARCH FOR PHOTO-INDUCED PHASE TRANSITON WITH ULTRAFAST RESPONSE BASED ON ELECTRONIC- STRUCTURAL COUPLED PROBES Special Thanks to Organizers S. Koshihara, Tokyo Institute of Technology

2 Achieved under collaborations with Professor K.Miyano Group, Professor T.Arima (Univ.Tokyo) Professor H.Yamochi Group (Kyoto Univ.) Professor D.Miller Group, Dr.S.A.Hayes (Univ.Toronto & MPG) Professor R.Kato Group (RIKEN) Professor Y.Hayashi Group, Prof. M.Hada (Okayama Univ.) Professor K.Tanaka Group, Prof. H.Hirori (Kyoto Univ.) Professor K.Nakamura, K.Onda, Y.Okimoto & T.Ishikawa (Tokyo Tech.) Dr. R.Fukaya, Dr. K.Fkumoto & Dr. M.Hoshino (JST CREST) Co-workers at KEK-PF, AR Professor S.Adachi Group, Professor S.Nozawa

3 This talk includes confessions of one Japanese Professor: How many big mistakes he has made in grappling with materials, and how his colleagues corrected them,,. Souvenirs bought at shop in Humboldt Univ., Berlin

4 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? Free from thermal effect utilizing photo-induced hidden phase/state via initial quantum dynamics is an attractive target.

5 E Traditional (Classical) PIPT Relaxation Thermalization Not-coherent Quasi-Stable State (False Ground State) Q

6 E Traditional (Classical) PIPT 2 Quasi-Stable State (False Ground State) Real Ground State Q

7 What can be expected for ultrashort pulse? Excitation light is shorter than molecular vibration (What is the definition of thermal effect in such time scale?) Machining by 100fs light Top of a match Excitation by 100fs pulsed laser 発火 Excitation by CW laser M.Takesada and S.Koshihara Look Japan April 2001

8 New Class of PIPT: Characteristic of Ultrafast Excitation Quantum (Cooperative) Dynamics which leads to Hidden State E Quantum Dynamics Hidden State Q

9 New Excited Classstates of PIPT: may Characteristic be robust of Ultrafast against Excitation relaxation Quantum (dephasing, (Cooperative) etc) reflecting Dynamics strong interaction which leads (correlation) to Hidden and ultrafast State response within period of a elementary particle E vibration. Quantum Dynamics Hidden State It can be realized in realistic materials? If so, we can get the new research method for cooperative quantum phenomena which is counter part to ordinary Q way.

10 Quantum Dynamics on Excited State Surface E Complex Change in Freedom of Charge Freedom of Lattice(Orbital) Freedom ofspin Structure/ Orbital Spin hn Charge

11 Why electron (Charge+Spin)-lattice strongly coupled system is an attractive target for the research of a hidden Phase/State? 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 hn Dielectric

12 DOE(USA) also reported about importance of research on hidden phase. (December 2007)

13 Figs.13 and 42:Report of NTT DATA INSTITUTE OF MANAGEMENT CONSULTING, Inc.:Feb Importance from the view point of application: How large amount of energy (electricity) will be necessary for information traffic, treatment and storage 2025:10GB/person/Day 2013:100MB/person/Day 2050: 0.21TkWh/year 2025: 0.15TkWh/year 2010: 0.08TkWh/year Total electric power consumption in Japan: TkWh/year (2013)

14 Typical Example of CLASSICAL PIPT S. Koshihara, Y. Tokura, K. Takeda and T. Koda: Phys. Rev. Lett. 68, 1148(1992).

15 Sub-micrometer Phase Separation induced by PIPT Photo taken by my Boss (Prof. Y.Tokura) in 1984.

16 Bistability in the ground state

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18 Utilization of Hysteresis Threshold Intensity Importance of Carrier Doping (not Wannier Exciton Doping)

19 K-TCNQ (Half filled SpinPeierls system) ns study TTF-CA (Half filled CT system): ns study Phys.Rev.B 44 (1991) 431 Phys.Rev.B 42 (1990) 6853 A - A - A - A - A - A - A - A - hn A - A - A - A - A - A - A - A - A - D + A - D + A - D + A - D + hn A 0 D 0 A 0 D 0 A 0 D 0 A 0 D 0

20 Various systems have been found for Photo- Magnetism in False Ground State. Co,Fe Cyanide O.Sato et.al. Science 272 (1996) 704 Mn-O (I-M transition) : K.Miyano et.al. PRL 78 (1997) 4257 Spin Crossover Complex PRL 103, (2009),,, PRL 84 (2000) 3181 (In,Mn)As: PRL 78 (1997) 4617

21 Appearance of Ultra-fast phase conversion Something different from Classical PIPT, but, but,,, VO 2 I-to-M PRL87 (2001) Half Metal Sr 2 FeMoO 6 PRL85 (2000) 1986 Similar Example Lu 2 V 2 O 7 : J. Phys.Chem. of Solids 62 (2001) 325 Importance of soft correlated matters. Halogen-Bridged Nickel-Chain Compound PRL 91 (2003) 57401

22 New Class of PIPT: Characteristic of Ultrafast Excitation E Important role of Hidden State as an origin of gigantic photo-response Quantum Dynamics Hidden State Quantum Dynamics which leads to Hidden State Cooperative-Quantum Dynamics in realistic materials? Q

23 Why (EDO) 2 PF 6 is important for the study of PIPT? A noble metal (M) insulator (I) transition (Charge Order:CO) accompanied with multi-instability at 280K What occurs in a system with multicooperativity by photo-excitation? Non-equilibrium Melting of CO!

24 Ultrafast melting of Ice of Charge in organic CT salt: Hidden state of (EDO) 2 PF 6 Quasi-1D, 3/4-filled organic conductor with strong electron-lattice coupling 1mm 280 K DR/R=1 means 100% change! Cooperative melting of electreon & lattice Ota, Yamochi, and Saito, J. Mater. Chem. 12, 2600, (2002) M. Chollet et al. Science, 307, 86 (2005)

25 CO melting (M-I transition) by photo-excitation (EDO-TTF) 2 PF 6 (T MI = 280 K) Pump:1.55 ev, E//b Photons/cm 2 Probe:E//b T = 180 K 1:Quite similar to thermally induced melting of CO 2:Highly efficient and fast conversion with 800nm excitation (a few ten mj/cm 2 pulse:1 photon for every few hundreds molecules)

26 Shinya could not believe so huge change and suspected of the mistake by students,,,

27 Photo-excited state is similar to the themally induced M phase? No! Photo-induced new CO state appears. Shinya could not predict such a new state (hidden state),,,,? DT charge ordered melted under strong e-e and e-ph interactions K.Onda et al. PRL 101 (2008)

28 Photoinduced Dynamics in Terms of Electronic Spectrum (Traditional Method) Experimental Data Model Calculation new band CT1 CT1 CT3 CT2 CT3 CT2 (0101)* charge order state K. Onda, S. Ogihara, K. Yonemitsu, et al. Phys. Rev. Lett. 101, (2008)

29 DR/R Reflectivity Photoinduced Dynamics in Terms of Vibrational Spectrum Pump:800 nm E stack HT phase (0.5) LT phase (0, +1) 1 ps 20 ps 300 ps Wavenumber (cm -1 ) N. Fukazawa, et al. J. Phys. Chem. C, 116, 5892 (2012)

30 Especially for dynamical structural change in organic crystal, usage of laser based electron diffraction is essential. Polarized Microscopic Images EDO (100nm) 100-nm thick samples, 50 kev 1 khz

31 Structural Change Revealed by fs-electron Diffraction move stay stay move move move move 1 ps hn 100 ps DT mov e M. Gao et al. Nature, 496, 343 (2013)

32 Even Coherent Control at 180K is possible! (Role of Quantum Dynamical Process is important) phase locked double pulse in-phase excitation e> g> Delay pump pulse elec. state out-of-phase excitation e> g> pump pulse elec. state Delay

33 Phase-controlled Double Pulse Excitation in-phase -DR/R DR/R pump out-of-phase (fs) Delay Time (fs) Pump1 Pump2 Probe Pump1 Pump2 Probe scan fixed fixed scan τ fs 30 fs Delay Time Y.Matsubara et al. PHYSICAL REVIEW B 89, (R) (2014)

34 A hidden phase/state is never limited for organic materials. (Nd,Sr) MnO 6 hn T Ferromagnetic Metal High Temp. Phase Nd 0.5 Sr 0.5 MnO 3 /SrTiO 3 (011) (NSMO/STO(011)) CO-OO Insulator Low Temp. Phase

35 Nature Materials 10 (2011) 101

36 Gigantic fs photo-response (<400 K) in BaCo 2 O 5.5 (R=Sm, Gd and Tb) Hidden IS or HS magneto polaronic state? cm -1 ) cm -1 ) cm -1 ) K K 1 0 c ps 300 K c c 0 ps 300 K (c) Sm 0 ps 400 K K h (ev) (a) Tb (b) Gd (Collaboration with Prof. T.Arima (Sample) and Prof. S.Ishihara (Theory) Groups (Tohoku Univ.)) Co 3+ d 6 e g t 2g LS(S=0) LT phase HS(S=2) IS (S=1) HT phase M-I transition at 360 K accompanied with magnetic change Theory: Kanamori, Matsueda, Ishihara PRL 107, (2011) Experiment: Y.Okimoto et al. PRB 84, (R) (2011)

37 Reflectivity Reflectivity Reflectivity Gigantic Photo-induced Absorption at Low Energy (never appears even at high temperature) (a) Tb 300 K 300 K 400 K (b) Gd 400 K 300 K 400 K (c) Sm 0 ps 0 ps 0 ps Normalized DR/R Normalized DR/R Normalized DR/R Energy (ev) 0 ps n p (Co site -1 ) ps n p (Co site -1 ) ps n p (Co site -1 ) cm -1 ) cm -1 ) K 400 K Y. Okimoto et al., Phys. Rev. B 84, (R) (2011) cm -1 ) c 300 K c c 300 K 0 ps 400 K 0 ps K h (ev) 0 ps (a) Tb (b) Gd (c) Sm

38 High Density HS Polaron State (Hidden Phase) Co 3+ LS (d 6 ) 0.4 (b) L-Spin (S=0) Theory I-Spin (S=1) H-Spin(S=2) HS Hole Electron N eff photo 0.2 thermal Electron transfer Y. Kanamori, H. Matsueda and S. Ishihara, Phys. Rev. Lett. 107, (2011)

39 A hidden phase/state is never limited for organic materials. Hidden phase (state/face?) plays a key role in Manganite (NSMO). Ground State(CO-OO phase) Thermally induced M Photo-induced(CO-OO new phase/state) H.Ichikawa et al. Nature Materials 10 (2011) 101. cm -1 ) cm -1 ) cm -1 ) K 400 K c c 300 K c 300 K 0 ps 400 K 0 ps 0 ps (a) Tb (b) Gd (c) Sm K h (ev) Gigantic fs photo-response (<400 K) in BaCo 2 O 5.5 (R=Sm, Gd and Tb) Hidden IS or HS magneto polaronic state? Theory: Kanamori, Matsueda, Ishihara PRL 107, (2011) Experiment:Y.Okimoto et al. PRB 84, (R) (2011)

40 These examples strongly suggest that Shin-ya has missed various hidden phase/state of materials (faces of Hecate). Shinya could not image,,,, Ultrafast bi-directional phase switching at room temperature utilizing hidden state in cuprate ladder system (R.Fukaya, Y.Okimoto et al., Nature Commun. 6:8519 DOI: /ncomms9519 Direct Observation of Collective Modes Coupled to Molecular Orbital Driven Charge Transfer (T. Ishikawa et al., Science 350 (2015) 1501)

41 Structural Modualtion after fs laser excitation Neutral dimer Single layer of unit cell: z = 0.25 to 0.75 viewvec = [ ]; 2 - dimer Science 350 (2015) 1501

42 Detailed Molecular Movie 1 Neutral Dimer +2 Dimer (1) Rotation of Pt(dmit) 2

43 Detailed Molecular Movie 2 Neutral Dimer +2 Dimer Pt (1) Rotation of Pt(dmit) 2 (2)Modulation of Pt-Pt distance Pt (2) Scarce change in Pt-Pt distance

44 Charge is monovalent-like, but structure is different (Appearance of Hidden State)

45 A Photo-induced Insulator in Cu Ladder System Chain Sr/Ca D c L 5c L Hole Spin Ladder a B b c a E c Hole pair Cu O a C F c Nature Commun. 6:8519 DOI: /ncomms9519

46 Reflectivity DR/R Reflectivity DR/R 0.6 A SCO After 1 ps ev Delay time (ps) Before photoexcitation Photon energy (ev) 100 K E c B SCCO Just after photoexcitation ev Delay time (ps) Before 290 K photoexcitation E c Photon energy (ev) 2.0

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48 B D A Sample: SCO 2nd 1st Dt Pump pulses C E

49 Organic Ferroelectric (Printable): [H-dppz][Hca] (Tsugumi Umanodan) Hydrogen bonding forms one-dimensional supramolecular chain of alternating proton-donor and proton-acceptor molecules [H-dppz][Hca]: Ferroelectricity at room temperature H 2 ca Chloranilic acid dppz 2,3-di(2-pyridinyl)- pyradine a c P S. Horiuchi et al., J. Am. Chem. Soc. 135, 4492 (2013). T c (402 K) Ferroelectric phase: Long range H + ordering Paraelectric phase: H + disordering

50 SHG Change by Visible Excitation 0.0 [H-dppz][Hca] [H-dppz][Hca] DI SH /I SH Pump: 530 nm (E c) SHG: 400 nm (E c) Delay Time (ps) DI SH /I SH Delay Time (ps) SHG1 = 2.5 ps SHG2 = 1280 ps Just after photoexcitation, SH intensity decreased by 30 %. The optical control of ferroelectricity, indicating the macroscopic polarization inversion with proton transition There are two kinds of the relaxation times. SHG1 = 2.5 ps SHG2 = 1280 ps

51 Mid-infrared vibration spectroscopy Delay Time (ps) Reflectivity C-O Frequency (cm -1 ) The band reflectivity reduced. Transient spectra Lorentz model (cm -1 ) C-O Delay Time (ps) Just after photoexcitation, frequency ( ) showed softening. showed hardening after 300 ps. After 300 ps, reflectivity increased at the band edge ( 1560 cm -1 ). The electronic state changed through intramolecular transition

52 Model for Relaxation Dynamics Photoexcitation 0 ps 2-5 ps 530 nm pulse excited the intramolecula transition in Hca - molecules. Molecular electronic state changed. SHG intensity reduced, indicating the macroscopic polarization inversion. (Hidden State?) C-O - stretching mode soften. Protons showed disordering. 300 ps 1.3 ns Softened mode showed hardening. (Another Hidden State?) Electron redistributed. Protons restore long range ordering.

53 Summary: 1: Shinya could not believe,,, Structure of a hidden phase/state of EDO has been surely observed by virtue of combined use of ultrafast spectroscopy and e-diffraction. 2: Shinya could not predict,,, Hidden phase/state seems to be playing common role for gigantic photo-response in strongly C-S-L(O) coupled systems. 3: Shinya could not image,,, Hidden states/phases generated by quantum dynamical process, widely play essential roles in famous strongly correlated systems. New materials and their exotic photo-responses are waiting for structural evidence combined with spin state probe!.

54 Of course, (Speaker want to emphasize) Collaboration with ultrafast spectroscopy is a key! 250 fs e-diffraction system in Okayama Univ. (Okayama-Tokyo Tech. Collaborative Lab.)

55 Important purpose of adventure in nano-world Map Map of materials world 塩野著 Appearance of Airplane ローマ人の物語 X Light excitation (Hidden State and its Quantum Dynamics) can become a new axis?

56 We may get the new research method for cooperative quantum phenomena which is counter part to ordinary way (New blue sky appearance). Thank you for your Tomorrow: attention! Quantum dynamics driven materials with gigantic and/or quantum fluctuations Until today: Stable (electronic) structural science Shift of paradigm maybe crash against tree in fog, after 1 fs, but, but, but,,,,