Metal adatom structures on semiconductor surfaces: Model ...
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Ralph Claessen Physikalisches Institut and Röntgen Research Center for Complex Materials (RCCM) Universität Würzburg, Germany
Metal adatom structures on semiconductor surfaces: Model systems for low-dimensional quantum matter
ECRYS 2014, Cargese, 18-08-2014
• Tomonaga-Luttinger physics in 1D • (non)Rashba physics in 2D • Mott-Hubbard physics in a 2D triangular lattice • Elemental topological insulator
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Ralph Claessen Physikalisches Institut and Röntgen Research Center for Complex Materials (RCCM) Universität Würzburg, Germany
Surfaces as "Quantum Simulators"
ECRYS 2014, Cargese, 18-08-2014
• Tomonaga-Luttinger physics in 1D • (non)Rashba physics in 2D • Mott-Hubbard physics in a 2D triangular lattice • Elemental topological insulator
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The Würzburg "nanoteam" and friends
SR experiments L. Patthey (SLS/PSI) X.Y. Cui J.H. Dil (U Zürich/EPFL/PSI) B. Slomski F. Meier Eli Rotenberg (ALS) A. Bostwick J.L. McChesney LT-STM R. Matzdorf (U Kassel) S. Mietke
J. Schäfer P. Höpfner C. Blumenstein S. Meyer
C. Loho M. Scholz T. Schramm J. Settelein T.E. Umbach
J. Aulbach A. Barfuß L. Dudy A. Dollinger M. Heßmann
Theory W. Hanke (U Würzburg) A. Fleszar Gang Li S.C. Erwin (Naval Research Lab)
work supported by
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Transition metal oxides - Mott-Hubbard physics - high-Tc superconductivity - CMR
- …
"Electronic crystals" and emergent quantum phenomena
Bechgaard salts: - CDW/SDW instabilities - Tomonaga-Luttinger
liquid
ET-salts: - magnetic frustration - spin liquid behavior
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ARPES
Direct experimental access to electronic structure
STM/STS
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Transition metal oxides - Mott-Hubbard physics - high-Tc superconductivity - CMR
- …
"Electronic crystals" and emergent quantum phenomena
Bechgaard salts: - CDW/SDW instabilities - Tomonaga-Luttinger
liquid
ET-salts: - magnetic frustration - spin liquid behavior
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Alternative approach: surfaces as model systems
Example: metal adatom (sub)monolayers on semiconductor surfaces
• epitaxial and self-assembled growth of 2D and 1D structures
• control and tunability: - substrate orientation - adatom/substrate combination - doping by coadsorption - …
model systems with "tunable" electronic and magnetic properties
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Atomic nanowires: Au/Ge(100)
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Interacting electrons in 1D
breakdown of the Fermi liquid concept
spin-charge separation
Tomonaga-Luttinger liquid as new paradigm
suitable materials for TLL behavior ?
Atomic nanowires: Au/Ge(100)
classical interaction in 1D: fatal
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Interacting electrons in 1D
breakdown of the Fermi liquid concept
spin-charge separation
Tomonaga-Luttinger liquid as new paradigm
suitable materials for TLL behavior ?
Atomic nanowires: Au/Ge(100)
e.g., organic CT salts: TTF-TCNQ
-0.2 0.0 0.2 0.4
-0.8
-0.6
-0.4
-0.2
0.0
E-E F (
eV)
k|| (Å-1)
-0.2 0.0 0.2
-0.8
-0.6
-0.4
-0.2
0.0
k|| (π/b)
photoemission
1D Hubbard model
Realization: anisotropic crystals
PRL 88, 096402 (2002)
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Realization: Au atom chains on Ge(100)
Interacting electrons in 1D
breakdown of the Fermi liquid concept
spin-charge separation
Tomonaga-Luttinger liquid as new paradigm
suitable materials for TLL behavior ?
PRL 101, 236802 (2008)
Atomic nanowires: Au/Ge(100)
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Interacting electrons in 1D
breakdown of the Fermi liquid concept
spin-charge separation
Tomonaga-Luttinger liquid as new paradigm
suitable materials for TLL behavior ?
PRL 101, 236802 (2008)
Atomic nanowires: Au/Ge(100)
Realization: Au atom chains on Ge(100)
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Atomic nanowires: Au/Ge(100)
"single domain" sample
PRB 83, 121411(R) (2011)
ARPES: 1D Fermi surface and "band" dispersion
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Atomic nanowires: Au/Ge(100)
STM: differential tunneling conductivity
Nature Phys. 7, 776 (2011)
gradual depression of spectral weight at zero bias
no structural or CDW phase transition below 585 K
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Atomic nanowires: Au/Ge(100)
Nature Phys. 7, 776 (2011)
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Atomic nanowires: Au/Ge(100)
differential tunneling conductivity scaled conductivity
dEdf
kTeVi
kTeVT
dVdI
⊗
+
+Γ
∝
2
221cosh
πααTLL scaling behavior:
kTeVvsT
dVdI .53.0
Nature Phys. 7, 776 (2011)
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Atomic nanowires: Au/Ge(100)
Playing the surface playground: "bounded Luttinger liquid": chain end effects? effect of local impurities dimensional crossover: 1D 2D carrier doping …
Au epitaxy
Vacancy
Impurity
Bridge
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α = 1.20
α = 0.61
chain end
"bulk"
Power law exponents in TLL theory (charge stiffness )
bulk:
chain end:
53.0)2( 141 =−+= −
ρρα KKbulk
42.1)1( 121 =−= −
ρα Kend
26.0=ρK
Atomic nanowires: Au/Ge(100)
Nature Phys. 7, 776 (2011)
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Y
Other examples of atomic nanowires
Au/Si(hhk)
Au double chains
antibonding bonding Au bands
spin-polarized Rashba bands
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Other examples of atomic nanowires
Au/Si(hhk)
"silicene nanoribbons" (cf. graphene)
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Other examples of atomic nanowires
Au/Si(hhk)
"silicene nanoribbons" (cf. graphene)
DFT: extra electron @ very 3rd Si edge atom with local moment and AFM order S.C. Erwin et al., Nat. Comm. (2010)
spin-integrated STM: confirms theory PRL 111, 137203 (2013
theory experiment
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Other examples of atomic nanowires
Au/Si(hhk)
13.3 Å
8×2 4×1
4 atoms
U = -1.0 V
CDW
300 K 65 K
In/Si(111)
prototypical CDW system H.W. Yeom et al. (1999)
In/Si(111)
following talk
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Revolving spins: Au/Ge(111)
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Revolving spins: Au/Ge(111)
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Spintronics without magnetism ?
spin-orbit coupling at surface: Rashba effect
search for Rashba-split metallic surface states on insulating substrate
Realization: √3×√3 Au/Ge(111)
PRB 83, 235435 (2011)
STM
Revolving spins: Au/Ge(111)
picture: J.H. Dil
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Revolving spins: Au/Ge(111)
PRB 83, 235435 (2011)
ARPES: mapping of bands and Fermi surface
metallic surface state on a semiconducting substrate
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Revolving spins: Au/Ge(111)
kll(Å-1) KM
ARPES SIS beamline, SLS
PRB 83, 235435 (2011)
band dispersions Fermi surface
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Revolving spins: Au/Ge(111)
kll(Å-1) KM
ARPES SIS beamline, SLS
PRB 83, 235435 (2011)
band theory LDA+SIC
Au Ge
spin-orbit splitting band dispersions
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Revolving spins: Au/Ge(111)
ARPES SIS beamline, SLS
PRB 83, 235435 (2011)
band dispersions Fermi surface
kll(Å-1) KM
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Revolving spins: Au/Ge(111)
PRB 83, 235435 (2011)
Fermi surface spin-resolved LDA
spin-integrated ARPES
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Revolving spins: Au/Ge(111)
PRL 108, 186801 (2012)
3D spin-resolved ARPES COPHEE @ SIS beamline, SLS
Fermi surface spin-resolved LDA
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Revolving spins: Au/Ge(111)
PRL 108, 186801 (2012)
3D spin-resolved ARPES COPHEE @ SIS beamline, SLS
non-Rashba behavior: in- and out-of plane spin rotations
similar to topological insulators
experimental SARPES spin vector results
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Revolving spins: Au/Ge(111)
PRL 108, 186801 (2012)
non-Rashba behavior: in- and out-of plane spin rotations
similar to topological insulators
experimental SARPES spin vector results
3D spin-resolved ARPES COPHEE @ SIS beamline, SLS
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isotropic Rashba term
hexagonal warping and spin-z component
radial rotation of planar spin
Spin texture of Au surface bands: striking similarity to the Dirac state of the topological insulator Bi2Te3
Fu, PRL 2009: DFT: Hexagonal Warping in Bi2Te3
Basak, PRB 2011: DFT: Radial Rotation in Bi2Te3
Revolving spins: Au/Ge(111)
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Physics of frustration: Sn/Si(111)
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Problem:
magnetic frustrations of local spin-1/2 moments on a triangular lattice
spin liquid? 120° AFM Néel order? other ordered states?
Physics of frustration: Sn/Si(111)
Realization: √3×√3 Sn/Si(111)
J. Settelein et al.
STM
?
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Physics of frustration: Sn/Si(111)
scanning tunneling spectroscopy (STS) J. Settelein et al.
metal (1/2 filled)
Sn 5pz
Nat. Comm. 4, 1620 (2013)
ARPES
LHB UHB
G. Li et al., PRB 83, 041104 (2011)
Mott insulator
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Physics of frustration: Sn/Si(111)
local moments → magnetic ordering ?
e.g., 120° Néel order Sn/Si(111)
degeneracy
band backfolding for 3x3 SDW
3x3 superstructure
Nat. Comm. 4, 1620 (2013)
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Physics of frustration: Sn/Si(111)
metal (1/2 filled)
Sn 5pz
ARPES
G. Li et al., PRB 83, 041104 (2011)
ARPES "shadow bands"
G. Li et al., Nat. Comm. 4, 1620 (2013)
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Physics of frustration: Sn/Si(111)
G. Li et al., PRB 83, 041104(R) (2011)
row-wise antiferromagnetic order
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Direct comparison of ARPES with DCA spectral function
Physics of frustration: Sn/Si(111)
confirms (short-range) collinear AF row-wise order
Nat. Comm. 4, 1620 (2013)
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Direct comparison of ARPES with DCA spectral function
Physics of frustration: Sn/Si(111)
confirms (short-range) collinear AF row-wise order
Nat. Comm. 4, 1620 (2013)
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Physics of frustration
Isotropic triangular Hubbard model
spiral magnetic
NMI (spin liquid)
chiral (d+id) superconductivity
NMI
Playing the surface playground:
group IV atoms on (111) surfaces: Sn, Pb on Si(111), Ge(111) tuning of correlation, bandfilling, spin-orbit coupling topological superconductivity ? …
example: superconductivity in
Pb/Si(111)
Zhang et al. , Nat. Phys. (2010) Uchihashi et al., PRL (2011)
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Topological insulators go elemental: 𝜶-Sn/InSb(001)
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Topological insulators (TIs)
spin-orbit coupling +
band-inverted insulator
conducting and spin-polarized surface/edge states in the gap
3D TIs with 2D surface states
2D TIs with 1D edge states
M. König et al., Science 318, 766 (2007)
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known 3D topological insulators: • Bi2X3 (X=Se, Te) • strained HgTe /CdTe(001) • …
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PRL 11, 157205 (2013)
known 3D topological insulators: • Bi2X3 (X=Se, Te) • strained HgTe /CdTe(001) • …
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PRL 111, 157205 (2013)
known 3D topological insulators: • Bi2X3 (X=Se, Te) • strained HgTe /CdTe(001) • … predicted: • strained α-Sn /InSb(001)
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PRL 111, 157205 (2013)
ARPES: topological surface states and Dirac cone
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PRL 111, 157205 (2013)
Identification of the topological character: spin-polarized ARPES
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PRL 111, 157205 (2013)
Doping effects: - intrinsic p-doping by In diffusion - counter-doping with Te, acts also as surfactant
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Sn as 2D topological insulator: stanene
stanene = Sn bilayer (cf. graphene) control parameters: - strain
- dangling bond saturation (sp2 vs. sp3)
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Metal adatoms on semiconductor surfaces as Quantum Simulators • experimentally well-controlled
• "tunable" properties
• ideally suited for ARPES and STM/STS
• examples: - Fermi liquid breakdown in 1D - (non-)Rashba physics in 2D - Mott-Hubbard physics in frustrated geometries - elemental topological insulator
• perspectives: - doping/bandfilling effects - 1D-2D crossover - spin-orbit coupling - topological physics - …
Take home message
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