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11/13. Development of ferrite-based electronic-phase-change devices. Tanaka lab. Tatsuya Hori. What is Mott insulator ?. Hubbard model. As U increases. U : Coulomb repulsion t : Transfer integral . Localization ( U ) vs Delocalization ( t )

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11/13

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  1. 11/13 Development of ferrite-based electronic-phase-change devices Tanaka lab.Tatsuya Hori

  2. What is Mott insulator ? Hubbard model As U increases U : Coulomb repulsion t : Transfer integral Localization (U) vs Delocalization (t) U > t insulator with immobile electrons

  3. Electronic phase change External stimuli (T, H, E, n) H2O : Electrons : Insulator Metal New promising principles to create devices

  4. Electronic-phase-change devices Pr0.7Ca0.3MnO3 Fe3O4 However, device operations have so far been limited at low temperature (<<RT) ! Fe3O4: S. Lee et al., Nature Mater.,7, 130 (2008). PCMO: A. Asamitsuet al., Nature,388, 50 (1997).

  5. A candidate material : layered ferrite RE = Y, Dy…Yb, Lu Fe2.5+ (Fe3+:Fe2+=1:1) +or RE ? O Fe RE/O layer + Interaction Fe/O bilayer ~320 K ~500 K Charge-ordered (immobilized) state at room temperature N. Kimizuka et al., Solid State Commun., 15, 1321 (1974). 吉井et al.,日本結晶学会誌,51, 162 (2009).

  6. Electric-field-induced current switching Bulk crystal Electronic phase change Current switching L. J. Zeng et al., EPL84, 57011 (2008).

  7. Charge-ordered LuFe2O4 films Grown by pulsed-laser deposition Out-of-plane 2q/q scan Thermaly activated conduction LuFe2O4 c-axis oriented growth * (003) (006) (009)

  8. Current switching in the thin-film structure LuFe2O4 310K 300K 3D 2D Vsample A significant step to device applications K. Fujiwara, T. Hori, H. Tanaka, J. Phys. D: Appl.Phys., 46, 155108 (2013).

  9. Summary : current switching function ・Fabricated charge-ordered LuFe2O4 and YbFe2O4thin films. ・Induced the current switching effect in the thin film structure.

  10. Current work What’s my next target ? Another way to control the electronic phases by electric fields. E It’s electrostatic carrier doping.

  11. What is electrostatic doping ? VG Gate Metal Insulator Gate insulator Source Drain Mott insulator Substrate External control of the number of charge carriers and resulting electronic states (order vs disorder)

  12. Collapse of CO by chemical carrier doping LuFe2O4 Lu(Fe1.85Mg0.15)O4 Fe+2.5 (Fe+2 : Fe+3 = 1 : 1) Fe+2.5-dMg+2 Superlattice reflections Very sensitive to external carrier doping ! Y. B. Qin et al., J. Phys. Condens. Mater. 21, 015401 (2009).

  13. Key component : gate insulator Gate Gate insulator Source Drain Substrate Q = CV C = ere0S/d n2D = Q/S = ere0V/d

  14. Mott-transition needs large n2D at 0 K C. H. Ahnet al., Nature424, 1018 (2003).

  15. Ionic liquid – giant carrier accumulation capability VO2 Suitable for Mott-insulator systems ・High n2D ~ 1013~15 /cm2 ・No structural mismatching M. Nakano et al., Nature487, 459 (2012).

  16. Toward purely electronic Mott-transistors Structural phase transition NdNiO3 : MITcontrol (Charge-Disproportionation) Structural phase transition MIT S. Asanuma et al., APL97, 142110 (2010). Pursue and investigateMIT in the system without struct. phase trans.

  17. Device structure VG VD ID IG Ionic liquid* Separator SiO2 D S G REFe2O4 Cation YSZ(111) Substrate Anion A A *N,N-Diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide

  18. Fabrication processes Thin film fabrication Masking process Milling process Masking process Electrode attaching Separator SiO2 Masking process Ionic liquid* REFe2O4 D S G Separator attaching YSZ(111) Substrate Dropping ionic liquid

  19. Summary Through fabricating and evaluating Mott-transistors with REFe2O4 ・Reveal the nature of the field effect in Mott insulator systems.

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