Spin Polarized State in the Two- Dimensional Electron ... · Spin Polarized State in the...

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Spin Polarized State in the Two- Dimensional Electron Liquid at the Surface of SrTiO3 M. Gabay Schloβ Waldthausen 06/29-07/02/2015

Transcript of Spin Polarized State in the Two- Dimensional Electron ... · Spin Polarized State in the...

Page 1: Spin Polarized State in the Two- Dimensional Electron ... · Spin Polarized State in the Two-Dimensional Electron Liquid at the Surface of SrTiO3 . M. Gabay . Schloβ Waldthausen

Spin Polarized State in the Two-Dimensional Electron Liquid at the

Surface of SrTiO3

M. Gabay

Schloβ Waldthausen 06/29-07/02/2015

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M. Rozenberg, O. Hijano Cubelos

A. Santander-Syro, C. Martins

R. Valenti, H. Jeschke. M. Altmeyer Goethe Universität Frankfurt am Main

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A. D. Caviglia et al., Nature 456, 624 (2008)

kFl=1

200V

τSO=τel

ΕSO~ΕF

kFl~ 4 kFl~ 50

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J. Levy et al., Nature Communications 5, 5019 (2014)

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2DEGS in perovskite oxides Interface polar-non polar compounds

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-V

+V

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2DEGS in perovskite oxides Interface polar-non polar compounds Surface non polar material

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2DEGS in perovskite oxides Interface polar-non polar compounds Surface non polar material

Or cleaved surface in high vacuum

A. Santander-Syro et al. Nature 469, 189-193 (2011)

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A.F. Santander Syro et al. Nature 469, 189 (2011) Meevasana et al. Nat. Mater. 10, 114 (2011)

n2D~0.25 e/u.c

4 u.c < L < 8 u.c

F~100MV/m

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N.C Plumb et al

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A. Santander-Syro et al. Nature 469, 189-193 (2011)

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To appear in Phys. Rev. B (R) 2015

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Orbital symmetry reconstruction and strong mass renormalization in the two-dimensional electron gas at the

surface of KTaO3 A. F. Santander-Syro, et al.,Phys. Rev. B 86, 121107(R) , 2012

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A. F. Santander-Syro, et al. Nature Materials 13,

1085–1090 (2014)

∆kF ~ 0.1 A-1

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Splitting of the spin-polarized bands: ∆E=100 meV

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Oxygen vacancies at the boundary could be a unifying mechanism responsible for

the presence of the 2DEG

What role, if any do O vac play in

Spin-orbit effects (via relaxations or other processes)

Phys. Rev. B 87, 161102(R) (2013)

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Oxygen vacancies at the boundary could be the unifying mechanism responsible for

the presence of the 2DEG What role, if any do O vac play in

Magnetism 1

Nature physics 10.1038/nphys2737 (2013)

R. Pentcheva, PRB74, 035112 (2006)

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Oxygen vacancies at the boundary could be the unifying mechanism responsible for

the presence of the 2DEG

What role, if any do O vac play in

Magnetism 2

Phys. Rev. Lett. 111, 087204 (2013)

M. Salluzzo et al.

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Oxygen vacancies at the boundary could be the unifying mechanism responsible for

the presence of the 2DEG Modeling by

DFT for slabs in the presence of O vac (relaxed

structures)

Finite cluster analytical calculations (assess most relevant orbitals)

Single O vac Double O vac

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Oxygen vacancies at the boundary could be the unifying mechanism responsible for

the presence of the 2DEG Modeling by

DFT for slabs in the presence of O vac (relaxed

structures)

Finite cluster analytical calculations (assess most relevant orbitals)

Single O vac

2DEG but no in-gap state

J. Shen et al. Phys. Rev. B 86, 195119, 2012

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Oxygen vacancies at the boundary could be the unifying mechanism responsible for

the presence of the 2DEG

H. Jeschke et al. New J. Phys. 17 (2015) 023034

divacancy - TiO2 termination - 1 vacancy in top layer - + 1 nearby

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Oxygen vacancies at the boundary could be the unifying mechanism responsible for

the presence of the 2DEG

H. Jeschke et al. New J. Phys. 17 (2015) 023034

divacancy - TiO2 termination - 1 vacancy in top layer - +1 nearby

Qualitative agreement with non spin-resolved ARPES spectrum Can we recover 1.3 eV peak?

Where do the extra states come from?

How about the spin sector?

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TiO2 terminated SrO terminated

Vertical di-vacancy

Experimentally, termination is a mixture of both

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• Include: Rotations, Oxygen-vacancies

• Tight-binding model • XY - periodic

(001) – 2x2x4 cluster

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Remove Vacancy

Remove 𝑑-𝑝 and 𝑝-𝑝 Displace Ti

Increase 𝐸𝑝

Avoid having e sitting on site of

vacancy

Change 𝑑𝑧2-𝑑𝑥𝑧-𝑑𝑦𝑧 energies

Some 𝑑 orbitals ‘see’ the effect of the new Ti local

neighbours

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Unperturbed

“Smoothly” removing the vacancy

Vacancy

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Results for 2 vacancies vertically aligned

SrO-terminated

𝜆 = 25𝑚𝑚𝑚

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Unperturbed

“Smoothly” removing the vacancies, significant change in some energy states

37 Vacancies

New states

State A

State B

State C

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{dX dY dZ dx2-y2 dz2 pX pY pZ}

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Dz2-P

State A

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{dX dY dZ dx2-y2 dz2 pX pY pZ}

State B

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State B

Dz2-P

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{dX dY dZ dx2-y2 dz2 pX pY pZ}

State C

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State C

Dxy

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• K-dependence?

EF

Calculated at

the Γ point

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Other configurations

TiO2 terminated; horizontal di-vacancy

SrO terminated;

SrO terminated; Vertical di-vacancy

TiO2 terminated; vertical di-vacancy

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TiO2 terminated SrO terminated

Ti O Sr O-Vac

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Surface of STO harbors puddles of either magnetic or non magnetic regions

Surface of STO is inhomogeneous : mixture of TiO2 and SrO terminations. Orbital selectiveness (t2g states lead to spin textures; eg states to magnetism) Fermi surface with mixed orbital character