Recent ARPES Results from 4d & 5d TMOs (Sr 2 RhO 4, Sr 2 IrO 4 ) Changyoung Kim Dept. Physics, Yonsei University

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1 Recent ARPES Results from 4d & 5d TMOs (Sr 2 RhO 4, Sr 2 IrO 4 ) Changyoung Kim Dept. Physics, Yonsei University

2 Effect of the Octahedra Rotation on the Electronic Structure of Sr 2 RhO 4 B. J. Kim 1, J. Yu 1, S. J. Oh 1, H. Koh 2, I. Nagai 3, S. I. Ikeda 3, C. Kim 1 School of Physics and Center for Strongly Correlated Materials Research, Seoul National University, Seoul, Korea 2 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA 3 National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki , Japan B. J. Kim, et al., PRL, 97, (2006).

3 Outline Background - (Sr,Ca) 2 RuO 4 ARPES data from Sr 2 RhO 4 Missing d xy Fermi Surface Comparison with Band Calculation Summary Octahedra Rotation Effect on the Electronic Structure

4 Phase diagram of Ca 2-x Sr x RuO 4 S. Nakatsuji et al, Phys. Rev. Lett. 84, 2666 (2000). Mott transition Orbital Selective Mott Transition (OSMT

5 Structural distortion of Ca 2-x Sr x RuO 4 Various ground states are realized by structural distortions.

6 4d transition-metal oxide Large spatial extent of 4d orbitals large bandwidth, large 10Dq. tends to be weakly-correlated. Low-spin configuration is expected. x 2 -y 2 3z 2 -r 2 Ca 2-x Sr x RuO 4 Sr 2 RhO 4 xy yz, zx

7 Rotation of Octahedra Rotation brings about: Doubling of the unit cell Decrease of M-O-M bond angle which cause: Band folding Bandwidth narrowing

8 Unit cell doubling and band folding 1D π/2a π/2a a 2a π/a 0 π/a 2D (π,π) Γ

9 Band width narrowing Octahedra rotation t Decrease of M-O-M bond angle Metal, small U/W Decrease in hopping energy t t Increase in U/t Insulator, large U/W

10 ARPES data on Ca-doped SRO S.-C. Wang et al. PRL 93, (2004) Sr 2 RuO 4 Ca 1.5 Sr 0.5 RuO 4 ARPES signal is generally broad and weak.

11 Sr 2 RhO 4 Share same crystal structure with Sr 2 RuO 4. 5 electrons in 4d orbitals. Rotation angle ~ 10º. No supeconductivity. Sr 2 RhO 4 presents an opportunity to study the effect of rotation without disorder.

12 Electrical resistivity Similar to ρ(t) in Sr 2 RuO 4 ρ ab (μωcm ) (b) 30 ρ c (mωcm) 0 Sr 2 RhO 4 T (K) Sr 2 RhO ρ ab (μωcm) T 2 (K 2 ) T 2 (K 2 ) ρ c T (K) ρ c (Ωcm ) Large anisotropy ρ c / ρ ab (3K) = 2400 T 2 - dependence Fitting with ρ = ρ 0 +AT 2 ρ ab (T ) ρ c (T ) ρ 0 = 8.6 μωcm A ab = μωcm/k 2 ρ 0 = 20.1 mωcm A c = μωcm/k ρ ab 0.1 Below ~250 K, ρ c decreases with lowering temperature T (K) No superconducting transition was observed down to 36 mk. Sr 2 RhO 4 is a two-dimensional Fermi liquid.

13 Expected FS of Sr 2 RhO 4 By doping one electron: (rigid-band model) α Sr 2 RuO 4 Sr 2 RhO 4 FS of Sr 2 RuO RhO 4 β γ Hase et al. J. of solid state chemistry 123,186 (1996) We expect basically similar FS topology in Sr 2 RhO 4

14 ARPES measurements High energy ARPES ALS BL 7 Analyzer : Scienta 100 Temperature : 40K Total Energy Resolution : 40 mev Angular Resolution : 0.25 o Photon energy : 85 ev low energy ARPES Sample cleaved in situ SSRL BL Analyzer : Scienta 2002 Temperature : 20K Total Energy Resolution : 40 mev Angular Resolution : 0.25 o Photon energy : 20 ev Sample cleaved in situ

15 FS of Sr 2 RhO 4 M X X Fermi Surface Mapping Γ M Γ M Γ X Binding Energy (ev) Missing xy-band(g) FS in Sr 2 RhO 4! B.J. Kim et al.

16 LDA calculation WITHOUT distortion (rotation of octahedra) a hole pocket formed by xz/yz orbital band. (α) an electron pocket formed by x 2 - y 2 orbital band. (δ) two electron pockets formed by xy (γ) and yz,zx band (β) Occupation : α 94.8% β 66.8% γ 72.5% δ 7.1%

17 Effects of the rotational distortion undistorted undistorted +band folding distorted exp and calc. LDA calculation shows disappearance of xy-fs (γ) and x 2 -y 2 FS (δ). B. J. Kim, et al., PRL, 97, (2006).

18 Other s result F. Baumberger et al., PRL 96, (2006)

19 Effects of the rotational distortion B. J. Kim, et al., PRL, 97, (2006).

20 Effects of the rotational distortion B. J. Kim, et al., PRL, 97, (2006).

21 xy-band Γ Γ X X Observation of xy-band sunken under E f

22 What about (Ca,Sr) 2 RuO 4? - LDA Primitive unit cell supercell 6 o rotated 12 o rotated E. Ko, et al., to appear in PRL

23 Summary Sr 2 RhO 4 Rotation of the octahedra leads to hybridization of xy and x 2 -y 2 bands. Hybridization of xy and x 2 -y 2 bands results in: (1) transfer of electrons from yz/zx to xy band and (2) disappearance of the xy Fermi surface. e g states play vital role in determining electronic structures near E f, and therefore should be included in the theoretical models that deals with 4d TMOs.