ultrahigh-resolution spin-resolved arpes of novel low-dimensional systems seigo souma tohoku...
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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-Spain
Anomalous electron spin phenomena
Spin dependence of electronic structure
Rashba effect SpintronicsTopological insulator
Bi2Te3
Y.L.Chen et al., Science 325 (2009) 178.
€
Beff =α
gμB
ky
−kx
⎛
⎝ ⎜
⎞
⎠ ⎟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,↓)
2
Spin-splitting of surface Rashba effect
∇V= (0, 0, Ez)
Surface Rashba effect
Spin-orbit interaction
surface potential
Effective magnetic field
€
Beff ~ (∇V × p)
spin-resolved ARPES
Time reversal symmetry
E(k,↑) = E(-k,↓)
€
ˆ H SO = α Rσ ⋅ (∇V × p)
3
Space inversion symmetry
E(k,↑) = E(-k,↑)
Angle-resolved PES (ARPES)
e- freedom •Energy•Momentum
4
Detection of electron spin is
difficult !!Efficiency of instrument
goes down by 3-4 orderEnergy Resolution
100 meV
Spin-resolved ARPES
e- freedom •Energy•Momentum•Spin
5
Mott scattering
Mini Mott Detector
25 keV
c
6
Recent spin-resolved ARPES studies
VLEEDMott detector Mott detector(retarding-type) (high-energy type)
DE = 30 meVDE = 70 meVDE = 70 meV
(Fe(001)p(1x1)-O)
Sb(111) Bi1-xSbx(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 EK = 25 keV Mott scattering EK = 60 keV Electron diffraction EK = 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]
High-resolution spin-resolved photoemission spectrometer
7
A
B
C
D
Spin-resolved ARPES system
8
PzPy
(A,B)
(C,D)
Spin polarization
x
y
z
Spin-integrate ARPES
Energy
An
gle
Spin-resolved ARPES
spin up
spin down
Energy resolution at MCP
Aumetal
T = 3.5 K
Nbsuperconductor
simulationBCS function
Tc = 9.2 K
Gap size D = 1.5 meV
Broadening G = 200 meV
900 meV
T = 3.5 K
simulationFD function
Energy resolution at MCP
Xe I 8.437 eVXe I 8.437 eV
9
High-resolution spin-resolved photoemission spectrometer
10S. Souma et al., RSI 78 (2007) 123104.
Xe I photons 8-11 eV
Intensity 2 x 1013 photons/sec
Operation pass energy Ep = 1,2,5 eV
Energy resolution @ Mott
= 8-40 meV
Ep: pass energy
Energy resolution @ Mott
~ 0.008Ep eV
Side view
High-resolution spin-resolved photoemission spectrometer
11
Discharge problem
Au4fch1
ch2
12
ch2
ch1
Solving for discharge of Mott detector
Channeltron
Scattering chamber
Feed throughSafety cover
To HV supply
Au target
Focus cup
Channeltron
Scattering chamber
Focus cup25000 V2200 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 channeltron
Test measurement with gold sample
ch A
ch B
ch C
ch D
AuHe Ia
T=300KEp 10eV
ch A
ch B
ch C
ch D
AuT=10K
Ep 1eV
Xe I 8.437 eV
14
Energy resolution @ Mott= 8 meV
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.
semimetalSurface
peculiar metalBi, Sbbulk
15
Crystal structure of Bi
16
Previous spin-resolved ARPES studiesBi(111) film
H. Hirahara et al., PRB 76 (2007) 153305.
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
17
ARPES spectra of Bi(111) surface
surface BZ
bulk BZ
(111)
Xe I (8.436 eV)T = 30 K
Experiment
18
Band structure of Bi(111) surface
19
Spin-integrate band structure of Bi(111) surface
20
Bin
ding
Ene
rgy
(eV
)
0.10
0.15
0.20
0.05
EF
Wave vector kx (Å-1)0.0-0.2-0.8 -0.6 -0.4 0.2
Electronic structure near EF of Bi(111) surface
Wave vector kx (Å-1)0.0-0.2-0.8 -0.6 -0.4 0.2
Wav
e ve
ctor
ky
(Å-1)
0.0
0.1
0.05
-0.05
hole pocketelectron pocket
hole pocket
electron pocket
21
Spin-resolved ARPES of Bi(111) surfaceB
indi
ng E
nerg
y (e
V)
0.1
0.2
EF
-0.2-0.4 0 0.2
BG
Wave Vector kx (Å-1)
y
z
up spin
down spin
z directionInte
nsit
y (a
rb. u
nits
)
Binding Energy (eV)0.10.2 EF
up spin
down spin
Inte
nsit
y (a
rb. u
nits
)
y direction
Bin
ding
Ene
rgy
(eV
)
0.1
0.2
EF
Wave Vector kx (Å-1)-0.2
-0.4
0 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 structureno bulk projection at G near EF23
Band structure near EF of Sb(111) surface
24K. Sugawara et al., PRL 96 (2006) 046411.
Band structure near EF of Sb(111) surface
25K. Sugawara et al., PRL 96 (2006) 046411.
Surface band of Sb(111) at G point
2nd derivative
26K. Sugawara et al., PRL 96 (2006) 046411.
Spin-resolved ARPES spectra of Sb(111)
spin up
spin down
Bulk band
Surface band
27K. Sugawara et al., PRL 96 (2006) 046411.
SUMMARYSpin-resolved ultrahigh-resolution ARPES study of
Rashba effect on semi-metal surface
•Energy resolution DE= 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