Seigo Souma Tohoku University May 31 2010 A Takayama K Sugawara T Sato and T Takahashi Collaborators 1 WS10ETLODs ValenciaSpain Anomalous electron spin phenomena Spin dependence of electronic structure ID: 500306
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Slide1
Ultrahigh-resolution spin-resolved ARPES of novel low-dimensional systems
Seigo
Souma
Tohoku
University
May 31, 2010
A. Takayama, K. Sugawara, T. Sato, and T. Takahashi
Collaborators:
1
WS10-ETLODs, Valencia-SpainSlide2
Anomalous electron spin phenomena
Spin dependence of electronic structure
Rashba
effect
Spintronics
Topological insulator
Bi
2
Te
3
Y.L.Chen
et al
.,
Science
325
(2009) 178.
Spin-orbit interaction
High-resolution spin-resolved ARPES
Electronic-field induced spin-current
Rashba
term
Spin switch via S.O. interaction
Edge state (surface state)
Time reversal invariant
E
(
k
,
↑
)
=
E
(-
k
,
↓
)
2Slide3
Spin-splitting of surface
Rashba
effect
∇
V
= (
0, 0, Ez)Surface Rashba
effectSpin-orbit interaction
surface potential
Effective magnetic field
spin-resolved ARPES
Time reversal symmetry
E
(
k
,
↑
)
=
E
(-
k
,
↓
)
3
Space inversion symmetry
E
(
k
,
↑
)
=
E
(-k
,↑) Slide4
Angle-resolved PES (ARPES)
e
-
freedom
Energy
Momentum
4Slide5
Detection of electron spin is difficult !!
Efficiency of instrument goes down by
3-4 order
Energy Resolution 100
meV
Spin-resolved ARPES
e
-
freedom
Energy
Momentum
Spin
5
Mott scattering
Mini Mott Detector
25
keVSlide6
c
6
Recent spin-resolved ARPES studies
VLEED
Mott detector
Mott detector
(retarding-type)
(high-energy type)
D
E = 30
meV
D
E = 70
meV
D
E = 70
meV
(Fe(001)p(1x1)-O)
Sb(111)
Bi
1-x
Sb
x
(x=0.13)
[9] A.
Nishide
et al., PRB
81
(2010) 041309(R).
[8] T. Okuda et al., RSI
79
(2008) 123117.
[1] K.
Iori
et al., RSI
77
(2006) 013101.
[2] S.
Qiao
et al., RSI
68
(1997) 4390.
[3] T.
Kadono
et al., APL
93
(2008) 252107.
[1,2]
[3]
Au(111)
Mott scattering
E
K
= 25
keV
Mott scattering
E
K
= 60
keV
Electron diffraction
E
K
= 6
eV
[6] M.
Hoesch
et al., PRB
69
(2004) 241401(R).
[5] M.
Hoesch
et al., JESRP
124
(2002) 263.
[7] R.
Bertacco
et al., RSI
73
(2002) 3867.
[4] V. N.
Petrov
et al., RSI
68
(1997) 4385.
[4,5]
[6]
[9]
[7,8]Slide7
High-resolution spin-resolved photoemission spectrometer
7Slide8
A
B
C
D
Spin-resolved ARPES system
8
P
z
P
y
(A,B)
(C,D)
Spin polarization
x
y
z
Spin-integrate
ARPES
Energy
Angle
Spin-resolved
ARPES
spin up
spin
downSlide9
Energy resolution at MCP
Au
metal
T = 3.5 K
Nb
superconductor
simulation
BCS function
Tc = 9.2 KGap size
D
= 1.5 meV
Broadening
G
= 200
m
eV
900
m
eV
T = 3.5 K
simulation
FD function
Energy resolution at MCP
Xe I
8.437 eV
Xe I
8.437 eV
9Slide10
High-resolution spin-resolved photoemission spectrometer
10
S. Souma et al., RSI
78
(2007) 123104.
Xe
I photons8-11
eVIntensity
2 x
10
13
photons/sec
Operation pass energy
Ep
= 1,2,5
eV
Energy resolution @ Mott
= 8-40
meV
Ep
: pass energy
Energy resolution @ Mott
~ 0.008Ep
eVSlide11
Side view
High-resolution spin-resolved photoemission spectrometer
11Slide12
Discharge problem
Au4f
ch1
ch2
12
ch2
ch1Slide13
Solving for discharge of Mott detector
Channeltron
Scattering chamber
Feed through
Safety cover
To HV supply
Au target
Focus cup
Channeltron
Scattering chamber
Focus cup
25000 V
2200 V
1300 V
Spark
－
Solutions
－
1.
Re-polishing of high voltage electrodes
3
. Washing all parts
4
. Baking
5
. Conditioning of electrode’s surface by applying HV
Field emission
BG noise depends on voltage difference between the electrodes
Roughness of surface
2
. Coating of electrodes with
TiC
13
100,000 cps
@18kV
0.1 cps
@25kV
Noise at
channeltronSlide14
Test measurement with gold sample
ch
A
ch
Bch C
ch D
AuHe Ia
T=300K
Ep 10eV
ch A
ch B
ch C
ch D
Au
T=10K
Ep 1eV
Xe
I
8.437
eV
14
Energy resolution @ Mott
= 8
meVSlide15
Peculiar surface states of group-V semimetals
Surface
Rashba
effect
with S.O.
without S.O.
Yu. M.
Koroteev
et al
.
,
PRL
93
(2004) 046403.
semimetal
Surface
peculiar metal
Bi,
Sb
bulk
15
Crystal structure of BiSlide16
16
Previous spin-resolved ARPES studies
Bi(111) film
H.
Hirahara
et al., PRB 76 (2007) 153305.Slide17
In-situ preparation of Bi thin film on Si(111)
Si
(111) 7×7
Bi
(111) 1×1
LEED
substrate
Flash annealing
Bi thin film (80ML)
epitaxially
grown on Si(111) surface
17Slide18
ARPES spectra of Bi(111) surface
s
urface
BZ
bulk
BZ
(111)Xe I (8.436
eV)T = 30 K
Experiment
18Slide19
Band structure of Bi(111) surface
19Slide20
Spin-integrate band structure of Bi(111) surface
20Slide21
Binding Energy (
eV
)
0.10
0.150.20
0.05E
FWave vector kx (Å-1)
0.0-0.2
-0.8
-0.6
-0.4
0.2
Electronic structure near E
F
of Bi(111) surface
Wa
ve vector
k
x
(Å
-1
)
0.0
-0.2
-0.8
-0.6
-0.4
0.2
Wa
ve vector
k
y
(Å
-1
)
0.0
0.1
0.05
-0.05
hole pocket
electron pocket
hole pocket
electron pocket
21Slide22
Spin-resolved ARPES of Bi(111) surface
Binding Energy (
eV
)
0.1
0.2
EF-0.2-0.4
00.2
B
G
Wave Vector
k
x
(Å
-1
)
y
z
up spin
down spin
z
direction
Intensity (
arb
. units)
Binding Energy (
eV
)
0.1
0.2
E
F
up spin
down spin
Intensity (
arb
. units)
y
directionSlide23
Binding Energy (
eV
)
0.1
0.2
EF
Wave Vector kx (Å-1)-0.2
-0.40
0.2
Problem in Bi(111) surface state
Time reversal symmetry
E
(
k
,
↑
)
=
E
(-
k
,
↓
)
Degeneracy of surface band at
G
(
k
=0) point
Sb
(111)
Bi
(111)
Bi(111): surface band is
unclear at
G
due to
bulk band projection
ARPES
on Sb(111)
same crystal structure
no bulk projection at
G
near E
F
23Slide24
Band structure near E
F
of Sb(111) surface
24
K. Sugawara et al.,
PRL 96 (2006) 046411.Slide25
Band structure near E
F
of Sb(111) surface
25
K. Sugawara
et al
., PRL 96 (2006) 046411.Slide26
Surface band of Sb(111) at
G
point
2
nd derivative
26
K. Sugawara
et al
.
,
PRL
96
(2006) 046411.Slide27
Spin-resolved ARPES spectra of Sb(111)
spin up
spin
down
Bulk band
Surface band
27
K. Sugawara
et al
.
,
PRL
96
(2006) 046411.Slide28
SUMMARY
Spin-resolved ultrahigh-resolution ARPES study of
Rashba
effect on semi-metal surface
Energy resolution
D
E= 8 meV Observation of Spin-splitting of surface band on Bi and
Sb (111)Time reversal symmetry holds at
G
Surface
Rashba
effect on group-V semimetal surface