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 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 G-type AF state PM state (SrTiO3: L. F. Mattheiss, Phys. Rev. 181, 987 (1969).) ③ Fe ③ ③ O ③ ③ ③ ③ ⑤ ③ ⑤ ③ ⑤ DE Basis : 14 Basis : 28 G-type AF

Comparison with AIPES spectra Density of states Comparison with AIPES spectra Optical gap of LaFeO3 : Egap = 2.1 eV (T. Arima et al., PRB 48, 17006 (1993)) 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. 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

Comparison with ARPES results 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 Reconstruction-derived surface bands O 2p bands A. Chikamatsu et al. cond-mat/0503373.

Tight-binding band-structure calculation FM state PM state (SrTiO3: L. F. Mattheiss, Phys. Rev. 181, 987 (1969).) ③ Mn ③ ③ O ③ ③ ③ ③ ⑤ ③ ⑤ ③ ⑤ DE Basis : 14 Basis : 14 FM

Tight-binding calculation (G-X direction) Strong electron correlation eg ↑ bands t2g ↑ bands Reconstruction-derived surface bands O 2p bands Majority-spin bands Minority-spin bands eg↑ bands cross EF. (half-metallic behavior) ep-ed = -3 eV, eds-edp, = 0.41 eV, eps-epp = 0 eV, (pds) = -2.0 eV, (pps) = 0.60 eV DE = 4.6 eV ARPES Data: A. Chikamatsu et al. cond-mat/0503373.

ARPES form 3-dimensional materials kz kz kll kll Momentum parallel to surface kll Momentum perpendicular to surface kz z

Simulated band structure (88 eV) Dkz = 0 Dkz = 1/l Dkz = ∞ Finite escape depth l kz broadening (Lorentzian function)

Comparison with high-symmetry line (G-X) 88 eV (Dkz = 1/l) vs G-X direction The trace obtained at 88 eV nearly G-X direction Effect of kz broadening

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