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)