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Chang Young Kim Dept. of Physics, Yonsei U

Electronic Structure of Electron Doped Superconductor Sm 1.85 Ce 0.15 CuO 4 : Quantitative Analysis Based on ( p,p ) Scattering Model. Chang Young Kim Dept. of Physics, Yonsei U. Work done by…. ARPES S. Park , H.S. Jin, C.S. Leem (Yonsei) Peter Armitage (Geneva) B.J. Kim (SNU)

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Chang Young Kim Dept. of Physics, Yonsei U

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  1. Electronic Structure of Electron Doped Superconductor Sm1.85Ce0.15CuO4: Quantitative Analysis Based on (p,p) Scattering Model Chang Young Kim Dept. of Physics, Yonsei U

  2. Work done by… • ARPES • S. Park, H.S. Jin, C.S. Leem (Yonsei) • Peter Armitage (Geneva) • B.J. Kim (SNU) • H. Koh, Eli Rotenberg (ALS) • Donghui Lu (SSRL) • Sample • Hiroshi Eisaki (AIST)

  3. Outline Past work Interpretation in (p,p) scattering model New data and further understanding Summary

  4. Angle Resolved Photoemission Spectroscopy (ARPES) hv Electron Analyzer Z - q e Y Detector f X EDCs at different angles • Photoelectron kinetic energy is measured • Emission angle of photo electron is measured • Energy and emission angle are transformed into • momentum Angle (Momentum) Resolved PES

  5. ElectronDoped HTSC e e e e e e Phase Diagram

  6. Hole- vs Electron-doped (Structure) Cu2+ Cu2+ Nd3+/Ce4+ La3+/Sr2+ O2- O2- O2- O2- (Apical) (La,Sr) CuO (Nd,Ce) CuO 2 4 2 4 No apical oxygens!

  7. ARPES on Electron Doped HTSC First ARPES work: J. Allen et al. , PRL 70, 3155 (1993); D. M. King et al. , PRL 70, 3159 (1993). (On low quality of the samples grown by flux method) -0.8 -0.4 0 0.4 Binding Energy (eV) 8 year gap! • Recent ARPES work: • N. P. Armitage, PRL 86, 1126 (2001); 87, • 147003 (2001);88, 257001(2002). • T. Sato, Science 291, 1517 (2001); H. Matsui • PRL 94, 047005 (2005); H. Matsui PRL 95, • 017003 (2005)

  8. Fermi liquid? Pr2-xCexCuO4 thin film ARPES * For hole-doped: rab~ T ~ T2 depending on doping P. Fournier et. al.

  9. Sign change in RH Y. Dagan, PRL, 92, 167001 (2004)

  10. Main Valence Band hv = 16.5 eV T = 10 K Intensity (Arb. Unit) 0.6 0.4 0.2 0.0 Nd2-xCexCuO4 7 6 5 4 3 2 1 0 Binding Energy (eV)

  11. Fermi Surface Suppression kx • FS suppression at the intersection of AF Billiouin Zone Boundary (AFBZ) with the underlying FS • Coupling to a bosonic mode localized at Q=(p,p)? • If it is due to low energy Q=(p,p) bosonic mode, suppression is expected to exist on at the Fermi energy. ky Binding energy(eV) N. P. Armitage, PRL, 87,147003 (2001)

  12. Doping Dependence Binding Energy (eV) N. P. Armitage, PRL 88, 257001 (2002).

  13. Theory I Assuming Q=(p,p) scattering channel t-t’-t”-U(x) C. Kusko, PRB 66, 140513 (2002) Theory Exp

  14. More Theories (Hubbard or t-J models) PHYSICAL REVIEW B 72, 054504 (2005) • Many-body calculations produce similar results : FS reconstruction, shadow FS & band folding. • AF ordering is assumed PHYSICAL REVIEW B 66, 140513(R) (2002) PHYSICAL REVIEW LETTERS 91,186407 (2003) PHYSICAL REVIEW LETTERS 93,147004 (2004)

  15. Effect of Ordering <Degenerate perturbation theory> New Bragg plane

  16. With a static ordering. FS (Fig 1). Band structure along the blue arrow in Fig 1 (Fig 2). ordering - (p, p) scattering Fig. 1 (p,p) Q=(p,p) G (p,0) Fermi surface Fig.2 EF AFBZ Band Structure

  17. New Band Structure Fig. 1 • Reconstructed FS (Fig 1). • No electronic states at the Fermi energy where FS intersects the AFBZ. • Band structure along the cut (a) in Fig 1 (Fig 2). • Band structure along the cut (b) in Fig 1 (along the AFBZ, Fig 3). * Constant energy split (2Vpp) (a) Q=(p,p) (b) Fig. 2 Fig. 3 EF EF 2Vp,p 2Vp,p AFBZ

  18. Interpretation of Recent NCCO (x=0.13) 0 Binding energy(eV) 0.1 0.2 0.3 • FS suppression and band splitting – Assigned to AF spin correlation • Difficult to understand band structures near (p.0) in the model • No quantitative analysis. H. Matsui, PRL, 94, 047005 (2005)

  19. Going to ALS • Sample : SCCO (Tc=13K) • Sample preparation : FZ in situ cleaving • Analyzer: Scienta 100 • Temperature : 40 K • Total Energy Resolution: 40 meV • Angular Resolution: 0.25O • Photon energy : 85eV • Pass energy : 20eV • Manipulator: 6 axis motion, completely Motorized • Automated data acquisition ALS BL7

  20. Movie (Graphite) E M  K ky kx

  21. New Results from Sm1.85Ce0.15CuO4 0.0 0.0 0.5 0.5 1.0 1.0 1.5 1.5 1 ky G2 0 G -2 -1 0 kx (Å-1) ~1 eV total dispersion

  22. Violation of Luttinger Theorem? 1.5 1.0 ky 0.5 0.0 -1.5 -1.0 -0.5 0.0 kx • x=0.15 • 2*shaded/square=1.073 • 0.073 more than half filled • which is less than the doping • 2*(shaded+2*little square)/square=1.20 which is larger than 1.15

  23. Two Component Interpretation? Fermi Arc from Na-CCOC (hole-doped) F. Ronning et al., this exists only near (p,0) (p,p) (0,p) G (p,0) This never reaches EF near (p,0). Signature of AF fluctuation?

  24. Other Possibilities? • - reduced • hn=135eV • - reduced • - hn=85eV • - unreduced • - hn=85eV • FS suppression is a universal character of the electron doped HTSCs.

  25. Binding Energy (meV)` EF 100 2Vpp Along the AFBZ 200 300 EF 400 2Vp,p (p/2,p/2) (p,0) Fitting the Exp Data within the Model E (p,p) G 2Vp,p= 0.2eV ky kx

  26. 1 G ’ G ’ (p,p) G G ’ (p,0) (p,p) Q=(p,p) G FS reconstruction & FS volume Fig. 1 • Yellow dashed lines near the (p,0) points are reconstructed FS segments. • Fig 2 illustrates measurements of the filling factor. • Filling factor for the original FS is about 1.07, but filling factor within the (p,p) scattering model is about 1.13. • We observe an energy gap of ~10 meV at (p/2,p/2). This will be discussed later. Fig. 2 2 Fig. 3 (p,0.3p) Binding Energy (meV)` Intensity (arb. Units) (p/2,p/2) 500 400 300 200 100 EF

  27. Binding Energy (meV)` EF 100 2Vpp 200 (p,p) 300 400 (0,0) High Resolution Data Fig. 1 • Faint shadow FS (red arrow in Fig 1) • Also visible in the published data from NCCO (PRL 94, 047005). • E vs k plot along the white arrow in Fig 1, along the AFBZ. • Splitting of ~200 meV, consistent with high photon energy data from ALS Fig. 2 (p/2,p/2) (p,0)

  28. Fig. 2 Binding Energy (meV) EF 100 Intensity (arb. Units) 200 300 400 500 EF 200 400 (p,p) (0,0) Binding Energy (meV) Band Folding and Gap at the (p,p) Crossing Fig. 1 (p,p) (0,0) Fig. 3 • (p,p) cut. • Kink-like feature at about 50 meV. • Band folding • Gap due to band folding (p,0.3p) Binding Energy (meV)` Intensity (arb. Units) (p/2,p/2) 500 400 300 200 100 EF

  29. Binding Energy (meV) EF 200 (p,p) 400 32 (0,0) Problems with the model : band structure near (p,0) Fig. 1 • Band splitting energy decreases as we approach the original Brilliouin zone boundary. • This was interpreted as anisotropic spin correlation gap in an earlier work (PRL94,047005). • Band folding is not centered at the AFBZ contrary to what anisotropic spin correlation gap would predict. Therefore, anisotropic gap interpretation can not be right. AFBZ AFBZ AFBZ Fig. 2

  30. Interpretation of Recent NCCO (x=0.13) 0 Binding energy(eV) 0.1 0.2 0.3 • FS suppression and band splitting : AF spin correlation • Hard to understand band structures near (p.0) H. Matsui, PRL, 94, 047005 (2005)

  31. 1 G ’ G ’ (p,p) Electron pocket G G ’ (p,0) • Increasing doping, reducing FS suppression Hall Measurements Pr2-xCexCuO4 Y. Dagan, PRL, 92,167001 (2004) • Suggest quantum critical point at a critical doping near 0.165

  32. Summary • Comprehensive analysis based on (p,p) scattering model • Band splitting due to (p,p) scattering appears to be robust. • Vpp = ~100 meV (no momentum dependent scattering needed) • Doping and temperature dependence should clarify the issue

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