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

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

ARPES of La1-xSrxFeO3 thin films

ARPES spectra Experimental band structure (2nd derivative plot)

• eg bands (~ -1.3 eV) : significant dispersion• t2g bands (~ -2.4 eV) : weak dispersion• O 2p bands (-4 ~ -6 eV)

Inte

nsi

ty (

arb

. u

nits

)

-10 -8 -6 -4 -2 0Energy relative to EF (eV)

h = 68 eV

=

4o

12o

24o

t2g

eg

O 2p

32o

Tight-binding band-structure calculation

PM state(SrTiO3: L. F. Mattheiss,

Phys. Rev. 181, 987 (1969).)

G-type AF state

G-type AF

0 E⑤

③

③

Basis : 14 Basis : 28

③ ③

③

③

③

③

⑤ ⑤

FeO

③

Comparison with AIPES spectra

• Three main structures of the valence-band AIPES spectrum and the crystal field splitting of the O 1s XAS spectrum were reproduced.• The satellite structure could not be reproduced.

Density of states Comparison with AIPES spectra

Optical gap of LaFeO3 : Egap = 2.1 eV(T. Arima et al., PRB 48, 17006 (1993))

p-d = 0 eV, d-d, = 0.41 eV, p-p = 0 eV,(pd) = -1.5 eV, (pp) = 0.60 eV

E = 5.3 eV

DO

S

-8 -6 -4 -2 0 2 4Energy (eV)

'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

eg

t2g

EF (x = 0.4)(filling)

2.1 eV

total Fe 3d

Inte

nsity

(ar

b. u

nits

)-10 -5 0 5

Energy relative to EF (eV)

LaFeO3

ABC

Fe 3d

La 5d

tight-binding

PES XAS

sat.

DE

total Fe 3d O 2p

h = 600 eV

Expt.

• Band folding of Fe 3d eg bands could be reproduced. • Fe 3d t2g bands, O 2p bands … good agreement

Comparison with ARPES results

88 eV

X

X X

XM M

74 eVHole pockets

ARPES of La1-xSrxMnO3 thin films

ARPES spectra Experimental band structure (2nd derivative plot)

eg ↑ bands

t2g ↑ bands

Reconstruction-derived surface bands

O 2p bands

88 eV

(003) (103)

Z

X X

Z

R R

60 eV

Z R Z R

A. Chikamatsu et al. cond-mat/0503373.

Tight-binding band-structure calculation

PM state(SrTiO3: L. F. Mattheiss,

Phys. Rev. 181, 987 (1969).)

FM state

0 E⑤

③

③

Basis : 14Basis : 14

③ ③

③

③

③

③

⑤ ⑤

MnO

③

FM

Tight-binding calculation (-X direction)

p-d = -3 eV, d-d, = 0.41 eV, p-p = 0 eV,(pd) = -2.0 eV, (pp) = 0.60 eV

E = 4.6 eV

ARPES Data: A. Chikamatsu et al. cond-mat/0503373.

Reconstruction-derived surface bands

eg ↑ bands

t2g ↑ bands

O 2p bands

Strong electron correlation

Majority-spin bandsMinority-spin bands

eg↑ bands cross EF. (half-metallic behavior)

88 eV

(003) (103)

Z

X X

Z

R R

60 eV

Z R Z R

ARPES form 3-dimensional materials

kll

kll

Momentum parallel to surface

Momentum perpendicular to surface kz

z

kz

kz

kll

Simulated band structure (88 eV)

kz = 0 kz = 1/ kz = ∞

Finite escape depth kz broadening (Lorentzian function)

Comparison with high-symmetry line (-X)

88 eV (kz = 1/)vs

-Xdirection

2.52.01.51.00.50

Wave Number [Å-1

]

-10

-8

-6

-4

-2

0

2

En

erg

y re

lativ

e t

o E

F (

eV

)

h = 88 eV

The trace obtained at 88 eV

nearly

-Xdirection

Effect of kz broadening

Summary

• La1-xSrxMnO3

eg↑ bands cross EF. (half-metallic behavior) FM state

• La1-xSrxFeO3 eg↑ bands do not cross EF. (insulating behavior) G-type AF state

• The effect of kz broadening is important for the interpretation of ARPES results.

• Future work … Effect of matrix element

• In-situ photoemission measurements on single-crystal thin films of La1-xSrxFeO3 and La1-xSrxMnO3 were analyzed using tight-binding model calculation.