ペロブスカイト型Fe酸化物La1/3Sr2/3FeO3薄膜の光電子

tight binding計算によるペロブスカイト型
酸化物薄膜のARPESの解析
和達大樹、近松彰A、組頭広志A、
吉田鉄平B、溝川貴司B、藤森淳B、尾嶋正治A
東大理、東大工A、東大新領域B
科研費基盤研究A「単結晶薄膜化により物性を制御した強相関系
遷移金属酸化物の電子構造の研究」研究会
於東京大学柏キャンパス 2005年6月17日
ARPES of La1-xSrxFeO3 thin films
Experimental band structure
(2nd derivative plot)
ARPES spectra
t2g
h = 68 eV
O 2p
Intensity (arb. units)
eg
=
o
32
o
24
o
12
-10
0
-2
-4
-6
-8
Energy relative to EF (eV)
4
o
• eg bands (~ -1.3 eV) : significant dispersion
• t2g bands (~ -2.4 eV) : weak dispersion
• O 2p bands (-4 ~ -6 eV)
Tight-binding band-structure calculation
PM state
G-type AF state
(SrTiO3: L. F. Mattheiss,
Phys. Rev. 181, 987 (1969).)
③
③
Fe
O
③
③
⑤
Basis : 14
③
③
⑤
③
0
G-type AF
③
Basis : 28
③
⑤
DE
Comparison with AIPES spectra
Density of states
PES
h = 600 eV
LaFeO3
total
Fe 3d
EF (x = 0.4)
(filling)
C
Intensity (arb. units)
eg
DOS
Comparison with AIPES spectra
2.1 eV
t2g
B A
XAS
E
La 5d
D
sat.
Expt.
Fe 3d
tight-binding
total
Fe 3d
O 2p
'DDOS(U=5.3).DAT'
'DDOS3(3)(U=5.3).DAT'
'DDOS4(4)(U=5.3).DAT'
'DOS(U=5.3).DAT'
'DDOS(1)(U=5.3).DAT'
'DDOS(2)(U=5.3).DAT'
eg
t2g
-8
-6
-4
-2
0
Energy (eV)
2
4
Optical gap of LaFeO3 : Egap = 2.1 eV
(T. Arima et al., PRB 48, 17006 (1993))
DE = 5.3 eV
ep-ed = 0 eV,
eds-edp, = 0.41 eV, eps-epp = 0 eV,
(pds) = -1.5 eV, (pps) = 0.60 eV
-10
-5
0
Energy relative to EF (eV)
5
• Three main structures of the valenceband AIPES spectrum and the crystal
field splitting of the O 1s XAS spectrum
were reproduced.
• The satellite structure could not be
reproduced.
Comparison with ARPES results

X
X
M
88 eV

X
M
X
Hole pockets
74 eV
• Band folding of Fe 3d eg bands could be
reproduced.
• Fe 3d t2g bands, O 2p bands … good
agreement
ARPES of La1-xSrxMnO3 thin films
ARPES spectra
Experimental band structure
(2nd derivative plot)
eg ↑ bands
t2g ↑ bands
Reconstructionderived surface
bands
O 2p bands
Z
R
(003)
Z
R
(103)
X
X
88 eV
Z
A. Chikamatsu et al. cond-mat/0503373.
Z
R
R
60 eV
Tight-binding band-structure calculation
PM state
FM state
(SrTiO3: L. F. Mattheiss,
Phys. Rev. 181, 987 (1969).)
③
③
Mn
O
③
③
⑤
③
③
⑤
③
③
0
Basis : 14
FM
Basis : 14
③
⑤
DE
Tight-binding calculation (-X direction)
Strong electron correlation
eg ↑ bands
t2g ↑ bands
Reconstruction-derived surface bands
O 2p bands
Majority-spin bands
Minority-spin bands
DE = 4.6 eV
ep-ed = -3 eV,
eds-edp, = 0.41 eV, eps-epp = 0 eV,
(pds) = -2.0 eV, (pps) = 0.60 eV
eg↑ bands cross EF. (half-metallic behavior)
ARPES Data: A. Chikamatsu et al.
cond-mat/0503373.
ARPES form 3-dimensional materials
Z
kz
R
Z
(003)
R
(103)
X
X
kz
88 eV
Z
Z
R
R
kll
60 eV
kll
Momentum parallel to surface kll
Momentum perpendicular to surface kz
z
Simulated band structure (88 eV)
Dkz = 0
Finite escape depth l
Dkz = 1/l
Dkz = ∞
kz broadening (Lorentzian function)
Comparison with high-symmetry line (-X)
88 eV (Dkz = 1/l)
vs
-X direction
The trace obtained at 88 eV
nearly
2
-X direction
Energy relative to EF (eV)
0
Effect of kz broadening
-2
-4
-6
-8
h = 88 eV
-10
0
0.5
1.0
1.5
2.0
-1
Wave Number [Å ]
2.5
Summary
• In-situ photoemission measurements on single-crystal thin
films of La1-xSrxFeO3 and La1-xSrxMnO3 were analyzed using
tight-binding model calculation.
• La1-xSrxFeO3
eg↑ bands do not cross EF. (insulating behavior)
G-type AF state
• La1-xSrxMnO3
eg↑ bands cross EF. (half-metallic behavior)
FM state
• The effect of kz broadening is important for the interpretation of
ARPES results.
• Future work … Effect of matrix element

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