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M. Gabay

FROM STRANGE INSULATOR TO SPIN-ORBIT CONDUCTOR: UNVEILING ORBITAL-SELECTIVENESS AT THE LAO-STO INTERFACE. M. Gabay. Intensive course by A. Millis : OXIDE INTERFACES , April 4th, 2012 Ecole Polytechnique. Jean-Marc Triscone Andrea Caviglia Stefano Gariglio Nicolas Reyren A. Fête.

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M. Gabay

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  1. FROM STRANGE INSULATOR TO SPIN-ORBIT CONDUCTOR: UNVEILING ORBITAL-SELECTIVENESS AT THE LAO-STO INTERFACE. M. Gabay Intensive course by A. Millis: OXIDE INTERFACES, April 4th, 2012EcolePolytechnique

  2. Jean-Marc Triscone • Andrea Caviglia • Stefano Gariglio • Nicolas Reyren • A. Fête A. Santander-Syro M. Rozenberg • Barthélémy, M. Bibes

  3. The Band story • From diffusion to reconstruction…to confusion • Band inversion (t2g orbitals dxy dxz, dyz) • (Electric field?) confinement on STO side (mind the dielectric constant) • The carrier concentration puzzle • It takes two (types of bands) to tango

  4. Conduction depends on • Nature of the layers in contact (SrO/AlO2 vs LaO/TiO2) • Oxygen pressure • Mobility • Temperature • # of LAO layers

  5. A 2DEG can also be produced at the surface of pure STO A.F. Santander-Syro. Et al, Nature 469, 189, 2011 Nature Materials 7, 855 - 858 (2008)

  6. A.D. Caviglia, S. Gariglio, N. Reyren, D. Jaccard, T. Schneider, M. Gabay, S. Thiel, G. Hammerl, J. Mannhart, J.-M. Triscone, Nature 456, 624 (2008 ) Diffusion SO metal Horizontal scale: use conductivity at given T, to compare phase diagrams from different samples

  7. A few oddities revealed by transport measurements in LAO/STO heterostructures • A strange insulator regime • A weird quantum critical point • A dumbfounding parallel magnetotransport • Surface reconstruction that avoids polar catastrophe

  8. Looking for signs of localization in the Universe Y=| Y |eif • For the electronic states • For the Cooper pair state Rs=h/e2 Rs=h/4e2 Ioffe-Regel criterion for localization: kFl~1 In fact localization at T=0 in 2D even if kFl>>1

  9. 2D or not 2D d (~2-7nm) • Drude part  d< l (~ 5nm) • Weak localization part  d< Lin, Lso, Lh (~50 nm) • Interaction part  d<(D(ħ/kBT))1/2 From measurements of Rsheet, n2Dand MR

  10. 1.12≤kFl ≤4 as T varies from1.5K to 20K Courtesy of A. Caviglia

  11. Courtesy A. Caviglia

  12. In the strongly underdoped regime kFl~1

  13. The Band story • Band inversion (t2gorbitalsdxy dxz, dyz) • (Electric field?) confinement on STO side (mind the dielectric constant) • The carrier concentration puzzle • It takestwo (types of bands) to tango

  14. The Band story • Band inversion (t2gorbitalsdxy dxz, dyz) • (Electric field?) confinement on STO side (mind the dielectric constant) • The carrier concentration puzzle • It takestwo (types of bands) to tango

  15. The Band story • Band inversion (t2gorbitalsdxy dxz, dyz) • (Electric field?) confinement on STO side (mind the dielectric constant) • The carrier concentration puzzle • It takestwo (types of bands) to tango

  16. LAO STO z

  17. et al, Nature 469, 189, 2011

  18. xz, yz orbitals extend deeper inside the bulk

  19. The Band story • Band inversion (t2gorbitalsdxy dxz, dyz) • (Electric field?) confinement on STO side (mind the dielectric constant) • The carrier concentration puzzle • It takestwo (types of bands) to tango

  20. Courtesy of A. Caviglia Appl. Phys. Lett 94, 222111 (2009)

  21. pO2=10-5 mbar 10 uc

  22. pO2=10-3 mbar 10 uc Phys. Rev. Lett. 107, 056802 (2011)

  23. pO2=8 10-5 mbar Tc=0.12K

  24. The Band story • Band inversion (t2gorbitalsdxy dxz, dyz) • (Electric field?) confinement on STO side (mind the dielectric constant) • The carrier concentration puzzle • It takestwo (types of bands) to tango

  25. pO2=1.33 10-5 mbar 10 uc Phys. Rev. Lett. 103, 226802 (2009)

  26. A.D. Caviglia, S. Gariglio, N. Reyren, D. Jaccard, T. Schneider, M. Gabay, S. Thiel, G. Hammerl, J. Mannhart, J.-M. Triscone, Nature 456, 624 (2008 ) Diffusion SO metal

  27. WL correction to conductivity in the diffusive regime A large spin-orbit effect is uncovered T=1.5K Bin =F0/4pD in Bel =F0/4pD  BSO =F0/4pD SO Perpendicular magnetoconductance for different gate voltages A. Caviglia et al PRL 104, 126803 (2010)

  28. Rashbaspin-orbitcoupling H=( ExP ).s ħWSO = ESO~ 2EkF 1/SO =W2SO s(Drude)=s-Ds (WAL)-Ds(e-e)-Ds(Super)   m*=( h2/E)√ BSO/F0

  29. m*max ~2.2me

  30. ns~ 1014cm-2 xz, yz orbitals extend deeper inside the bulk PRL 106, 166807, 2011

  31. BRashba=( ExP ) xy band is isotropic in xy plane Model xz,yz bands as 1D, xz is // current / = - 1/8 (/EF)2 At Γ point, Exz~EF; Exy<<EF

  32. Courtesy A. Fête B=7T

  33. A. Caviglia et al PRL 104, 126803 (2010)

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