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FROM STRANGE INSULATOR TO SPIN-ORBIT CONDUCTOR: UNVEILING ORBITAL-
SELECTIVENESS AT THE LAO-STO INTERFACE.
M. GabayM. Gabay
Intensive course by A. Millis: OXIDE INTERFACESIntensive course by A. Millis: OXIDE INTERFACES,, April 4th, 2012April 4th, 2012
Ecole Polytechnique Ecole Polytechnique
Jean-Marc Triscone Andrea Caviglia Stefano Gariglio Nicolas Reyren
A. Fête
M. Rozenberg
A. Barthélémy, M. Bibes
A. Santander-Syro
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
The Band story
Conduction depends on
Nature of the layers in contact (SrO/AlO2 vs LaO/TiO2) Oxygen pressure Mobility Temperature # of LAO layers
Nature Materials 7, 855 - 858 (2008)
A 2DEG can also be produced at the surface of pure STO
A.F. Santander-Syro. Et al, Nature 469, 189, 2011
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 )
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 )
DiffusionDiffusion SO metalSO metal
Horizontal scale: use conductivityat given T, to compare phase diagrams from different samples
A strange insulator regime
Surface reconstruction that avoids polar catastrophe
A few oddities revealed by transport measurements in LAO/STO heterostructures
A weird quantum critical point
A dumbfounding parallel magnetotransport
|ei
For the electronic states For the Cooper pair state
Ioffe-Regel criterion for localization: kFl~1
Rs=h/e2
Rs=h/4e2
In fact localization at T=0 in 2D even if kFl>>1
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, n2D and MR
Courtesy of A. Caviglia1.12≤kFl ≤4 as T varies from1.5K to 20K
Courtesy A. Caviglia
In the strongly underdoped regime kFl~1
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
The Band story
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
The Band story
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
The Band story
STO LAO
z
et al, Nature 469, 189, 2011
xz, yz orbitalsextend deeperinside the bulk
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
The Band story
Appl. Phys. Lett 94, 222111 (2009)
Courtesy of A. Caviglia
pO2=10-5 mbar10 uc
Phys. Rev. Lett. 107, 056802 (2011)
pO2=10-3 mbar
10 uc
pO2=8 10-5 mbar
Tc=0.12K
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
The Band story
Phys. Rev. Lett. 103, 226802 (2009)
pO2=1.33 10-5 mbar10 uc
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 )
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 )
DiffusionDiffusion SO metalSO metal
T=1.5K
Perpendicular magnetoconductance for different gate voltages
A. Caviglia et al PRL 104, 126803 (2010)
WL correction to conductivity in the diffusive regime
A large spin-orbit effect is uncovered
BSO =0/4D SO
Bel =0/4D
Bin =0/4D in
Rashba spin-orbit coupling
ħSO = ESO~ 2EkF1/SO =SO
m* =( h2/E)√ BSO/0
H=( ExP ).
(Drude)=-(WAL)-e-e)-(Super)
m*max ~2.2me
PRL 106, 166807, 2011
ns~ 1014cm-2
xz, yz orbitalsextend deeperinside the bulk
BRashba=( ExP )
xy band is isotropic in xy planeModel xz,yz bands as 1D, xz is // current
At Γ point, Exz~EF; Exy<<EF
/ = - 1/8 (/EF)2
B=7T
Courtesy A. Fête
A. Caviglia et al PRL 104, 126803 (2010)
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