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K. Miyano and N. Takubo RCAST, U. of Tokyo

Bidirectional optical phase control between a charge-ordered insulator and a metal in manganite thin films. K. Miyano and N. Takubo RCAST, U. of Tokyo. What is it? motivation history of photoinduced transition sample development results future.

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K. Miyano and N. Takubo RCAST, U. of Tokyo

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  1. Bidirectional optical phase control between a charge-ordered insulator and a metal in manganite thin films K. Miyano and N. Takubo RCAST, U. of Tokyo What is it? motivation history of photoinduced transition sample development results future

  2. What is optical bidirectional phase control? photoexcitation pulse CW pulse …… manganite thin film COOI ’ FMM ’ COOI ’ …… COOI: charge- and orbital-ordered insulating state FMM: ferromagnetic metallic state

  3. motivation to understand ‘colossal’ response in strongly-correlated electron systems => “inhomogeneity” is the keyword* in particular, the effect of photoexcitation => ‘high energy’ excitation, far from equilibrium, instantaneous, high density, time-resolved spectroscopy …etc. => a ‘novel phase’ not accessible with ‘low energy’ stimuli e.g., T, H, E, … * E.Dagotto, New J. Phys. 7, 67 (2005)

  4. P: paramagnetic F: ferromagnetic AF: antiferromagnetic I: insulator history1: material Tomiokaet al. PRB53, R1689 (1996)

  5. 0 1 2 3 4 2: discovery ‘colossal effect’ AF COOI => FMM Laser pulse (5 ns) ↓ 108 Pr0.7 Ca0.3 MnO3 106 Resistance(Ω) 104 102 1 Time ( 100μ s) Tomioka et al. J.Phys.Soc.Jpn. 64, 3626 (1995)

  6. 3: problems not persistent = conducting state remains only while current is kept => phase transition? needs potential across electrodes at photoinduced transition => driven by current or photoexcitation? but WHY? local transition = IMT is 1st-order with lattice distortion => stress from the surrounding COOI undo the transition? => make it small or thin

  7. 7mm 4: ‘film’ is not good enough Pr0.5Ca0.5Mn0.96Cr0.04O3/MgO(001) photoinduced persistent conductivity MFM observation 80K 20K, 633nm, 1mW/cm2 H. Oshima, M. Nakamura, and K. Miyano, Phys. Rev. B63, 075111 (2001). film thickness H. Oshima et al., PRB 63, 075111 and 094420 (2001).

  8. sample development need a thin film with a clear 1st-order phase transition (IMT) i.e., forgive large lattice distortion => use (110) substrates (110) (001) tetragonal symmetry conserved shear deformation allowed Y. Ogimoto et al., Phys. Rev. B 71, 060403(R) (2005) Y. Ogimoto et al., Appl. Phys. Lett. 86, 112513 (2005) M. Nakamura et al., Appl. Phys. Lett. 86, 182504 (2005).

  9. tetragonal distortion predetermines the orbital = electronic states < c a ~ b ~ c > c on (001) substrates: x=0.5 C-type AFM FM A-type AFM Z. Fang et al. PRL (2000)

  10. clear transition a: in-plane b,c: tilted Nd0.5Sr0.5MnO3 magnetic transport structural Pr0.5Sr0.5MnO3 Wakabayashi et al., cond-mat/0506544

  11. Pr1-x(Ca1-ySry)xMnO3 (Single Crystals) bicritical point Y.Tomioka and Y.Tokura, Phys.Rev.B 66,104416(2002) Chaikin and Lubensky “Principles of condensed matter physics”

  12. bicritical point in thin film y=0.20 COO y=0.25 y=0.30 y=0.40

  13. (y=0.25) 0 T 1 T 3 T 5 T bulk vs. thin films phase diagrams Pr0.55(Ca1-ySry)0.45MnO3 TCO 2 T TC 4 T Y.Tomioka and Y.Tokura,Phys.Rev.B 66,104416(2002)

  14. photoinduced phase transition (to lower T phase) stable, persistent, no assisting field (y=0.25) Laser (100 pulses) Laser T=77 K YAG OPO Pulse Laser λ=637 nm 0.5 mJ/pulserep rate 10 Hz

  15. photoinduced phase transition: shot by shot one shot is not enough single shot · each shot is stable · effect of shots are cumulative threshold 1.95 eV multiple shots R(W) I (mJ/cm2)

  16. photoinduced phase transition: dynamics need to destroy charge gap = triggered by collapse of COO essential physics nucleation and growth <= pumping rate percolation all-optical write-erase memory transition heating

  17. future clear case of 1st-order phase transition involving charge + spin + lattice parameters: U + V + t (s, t)+ J + g + T + H + e • study: • nucleation and growth • scaling • time-resolved (pump and probe) • dynamics • electronic • magnetic

  18. summary establish film growth technique => clear COOI to FMM transition separate electronic excitation from heating => bidirectional phase control “soft and complex matter in solid form” => looks and feels hard but deformable colossal response vs inhomogeneity => understanding strongly-correlated electron systems? (optical measurement is a way to go)

  19. collaborators visitors in the past current work force Yasushi Ogimoto Manfred Fiebig Takao Mori Toru Tonogai Mikhail Milyaev Naoko Takubo Yusuke Uozu Hiroharu Tamaru Makoto Izumi Many students in the past other institutions Yoshinori Tokura Yasuhide Tomioka Hideki Kuwahara Yoichi Murakami

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