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Hard X-ray Photoelectron Spectroscopy (HAXPES) Of Correlated Materials A. Chainani, 1,2 Y. Takata, 1 * M. Oura, 2

Hard X-ray Photoelectron Spectroscopy (HAXPES) Of Correlated Materials A. Chainani, 1,2 Y. Takata, 1 * M. Oura, 2 M. Taguchi, 3 M. Matsunami, 3 R. Eguchi, 3 S. Shin, 3 1 Coherent X-ray Optics Lab 2 Advanced Photon Technology Division 3 Soft X-ray Spectroscopy Lab

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Hard X-ray Photoelectron Spectroscopy (HAXPES) Of Correlated Materials A. Chainani, 1,2 Y. Takata, 1 * M. Oura, 2

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  1. Hard X-ray Photoelectron Spectroscopy (HAXPES) Of Correlated Materials A. Chainani,1,2 Y. Takata,1* M. Oura,2 M. Taguchi,3 M. Matsunami,3 R. Eguchi,3 S. Shin,3 1 Coherent X-ray Optics Lab 2 Advanced Photon Technology Division 3 Soft X-ray Spectroscopy Lab RIKEN Harima Institute @ SPring-8 *deceased

  2. Acknowledgements For the development of HAXPES @ BL29XU Coherent X-ray Optics Lab. @ RIKEN SPring8 Center M. Yabashi, K. Tamasaku, Y. Nishino, D. Miwa, T. Ishikawa JASRI/SPring-8 E. Ikenaga (BL47XU), K. Kobayashi（BL15XU, NIMS) HiSOR, Hiroshima Univ. M. Arita, K. Shimada, H. Namatame, M. Taniguchi Musashi Inst. Technology H. Nohira, T. Hattori (Tohoku Univ.) VG SCIENTA

  3. Acknowledgements For Collaborations Titanates H. Hwang, H. Takagi Vanadates H. Hwang, K Motoya, Z Hiroi Manganites M. Oshima, Y. Tokura Cobaltates E. Takayama-Muromachi Cuprates T. Mochiku, K Hirata Ruthenates A. Yamamoto Ce compounds H. Sugawara Yb compounds N. Tsujii, A. Ochiai, S Nakatsuji Nitrides K. Takenaka

  4. Outline • 1) Introduction • Experimental Setup, Performance & Characteristics • Applications : Strongly correlated electron systems • 4) Future directions • 5) Summary

  5. Main Characteristic of HAXPES Large probing depth! Inelastic Mean Free Path (IMFP) of Electron (From NIST Database) 210Å （SiO2) IMFPs 1-4nm @ 1 keV 7-20nm @ 8 keV 140Å (SiO2) 30Å （SiO2) Al Ka Bulk sensitive Free from surface prep. Functional thin films Chemical depth analysis Embedded interfaces (non destructive)

  6. Early HAXPES with Cu Ka@8keV S. Hagstrom, C. Nordlimg, Chuck Fadley, S. Hagstrom, J. Hollander, K. Siegbahn, Phys. Lett. 9, 235 (1964) M. Klein, D. A. Shirley, Science 157, 1571 (1967)

  7. The first HAXPES with SR I. Lindau, P. Pianetta, S. Doniach & W E Spicer, Nature 250, 214 (1974) core level: possible valence band: impossible Au 4f

  8. Obstacle to development of HAXPES Small photoionization Cross Sections 1keV Rapid decrease! ~ 1/100 8keV

  9. High-energy Ce-3d photoemission: Bulk properties of CeM2 (M=Fe,Co,Ni) and Ce7Ni3 L. Braicovich, N. B. Brookes, C. Dallera, M. Salvietti, and G. L. Olcese Phys. Rev. B 56, 15047 (1997) @ESRF High-energy resonant photoemission and resonant Auger spectroscopy in Ce-Rh compounds@ESRF P. Le Fèvre, H. Magnan, D. Chandesris, J. Vogel, V. Formoso, and F. Comin Phys. Rev. B 58, 1080 (1998) Hybridization and Bond-Orbital Components in Site-Specific X-Ray Photoelectron Spectra of Rutile TiO2@NSLS J. C. Woicik, E. J. Nelson, Leeor Kronik, Manish Jain, James R. Chelikowsky, D. Heskett, L. E. Berman, and G. S. Herman, Phys. Rev. Lett. 89, 077401 (2002) Quadrupolar Transitions Evidenced by Resonant Auger Spectroscopy@HASYLAB J. Danger, P. Le Fèvre, H. Magnan, D. Chandesris, S. Bourgeois, J. Jupille, T. Eickhoff, and W. Drube, Phys. Rev. Lett. 88, 243001 (2002) Looking 100 Å deep into spatially inhomogeneous dilute systems with hard x-ray photoemission@ESRF C Dallera, L. Duò, L. Braicovich, G. Panaccione, G. Paolicelli, B. Cowie, and J. Zegenhagen Appl. Phys. Lett. 85, 4532 (2004) High resolution-high energy x-ray photoelectron spectroscopy using third-generation synchrotron radiation source, and its application to Si-high k insulator systems@SPring8 K. Kobayashi et al. Appl. Phys. Lett. 83, 1005 (2003) A probe of intrinsic valence band electronic structure: Hard x-ray photoemission@SPring8 Y. Takata et al. Appl. Phys. Lett. 84, 4310 (2004) HAXPES for Valence Bands with hn = 6 – 8 KeV.

  10. Experimental Setup

  11. How to gain in stability, resoluton, photoelectron intensity 1. High brilliance SR at SPring-8 2. High performance analyzer Pol. 55mm(V) 35mm(H) 1deg. attenuation length 10mm range IMFP 10nm range e- X-ray magic angle 1 deg. For linearly polarized light, angular intensity distribution of photoemitted electrons depends on the asymmetry parameter b b>0 at energies of several keV, for almost all subshells J.Yeh & I.Lindau At. Data.Nucl Data Tables 32, 1(1985) Their intensities have a maximum in a direction parallel to the electric polarization vector 3. Top-up injection 4. Matching the detection angle to the polarization of SR 5. Grazing incidence of X-rays 6. Well-focused X-ray beam 7. Low emittance operation

  12. Experimental setup at BL29XU in SPring-8 Y. Takata et al., Nuclear Instrum. and Methods A547, 50 (2005). T. Ishikawa et al., Nuclear Instrum. and Methods A547, 42 (2005). He flow cryostat to reduce sample vibration ★ excitation energy: 5.95 or 7.94keV, DE (hn): 55 meV ★ photon flux: ~5x1011 photons/sec @ 55(V)x 35(H) mm2 ★ analyzer:R4000-10kV (VG Scienta)

  13. Optics Layout for the HAXPES experiments

  14. VOLPE @ESRF DE=55±5 meV (Ep=50 eV) E/DE=140000! 5 sec 15min 30sec P. Torelli et al., Rev. Sci. Instrum. 76, 023909 (2005) High Energy Resolution & High Throughput (at 7.94 keV)

  15. VOLPE @ ESRF P. Torelli et al., Rev. Sci. Instrum. 76, 023909 (2005)

  16. KMC-1@ BESSY-II F. Schafers et al., Rev. Sci. Instrum. 78, 123102 (2007)

  17. Au 4f core levels @ BESSY-II

  18. Surface Insensitivity SiO2/Si(100) @ 7.94keV Si 2p BE:100eV Si 1s BE:1840eV 30sec 10sec SiO2 300sec Si : SiO2=42 : 1 SiO2 contribution < 3% Contribution of surface SiO2 is negligible! IMFP: Si=12nm, SiO2=16nm @ 8keV Si=1.8nm, SiO2=3nm @ 0.85keV Y. Takata et al. Appl. Phys. Lett. 84, 4310 (2004)

  19. Effect of Grazing Incidence of X-rays see also V Strocov, condmat/2013

  20. High Sensitivity (Buried Layer and Interface) LaAlO3:3ML LaVO3:3ML LaAlO3:30ML SrTiO3 5x10-7 Mb H. Wadati, A. Fujimori, H. Y. Hwang et al., PRB77, 045122 (2008)

  21. Large Probing Depth e- e- La0.85Ba0.15MnO3(20nm) SrTiO3 Sr 2p3/2(BE=1940eV) x65 H. Tanaka et al., Phys. Rev. B 73, 094403 (2006)

  22. Applications

  23. La1-xSrxMnO3 M-I transition with Colossal magnetoresistance A.Urushibara et al., Phys. Rev. B 51, 14103 (1995) H. Fujishiro et al., J. Phys. Soc. Jpn. 67, 1799 (1998)

  24. Feature absent in earlier soft-ray PES A.Chainani et al. Phys. Rev. B 47, 15397 (1993) T.Saitoh et al., Phys. Rev. B 56, 8836 (1997)

  25. UH D* D E F LH O 2p band MO6 Cluster model calculations Ground state：linear combination of 6 configurations 3d6C2 3d5C 3d6LC U 3d5L 3d6L2 3d4 １．Intra-atomic multiplets 4．Hybridization between coherent states at EF and Ru 3d orbitals : metallicity M. Taguchi G. Van der Laan et al PRB 23, 4369(1981) J. Imer & E. Wuilloud. Z Phys. B 66, 153 (1987) ２．Crystal Field ３．Hybridization between O 2p and Ru 3d orbital : Covalency 21

  26. Comparison with cluster calculations Good agreement! low BE feature CT from coherent states 2p53d5C V* = 0.28V Δ*= 3.6 eV AFM V* = 0.39V Δ*= 4.0 eV FM V* = 0.425V Δ*= 4.0 eV FM K. Horiba et al. Phys. Rev. Lett 93, 236401 (2004) V* = 0.25V Δ*= 3.0 eV AFI

  27. V1.98Cr0.02O3(experiments) Insulator Metal (hn : 5950 eV) (hn = Al Ka :1486.7 eV) M. Taguchi et al. PRB 71,155102(2005) K. Smith et al. PRB 50, 1382 (1994)

  28. V2O3 VB Photoemission (Coherent Peak) Coherent part DMFT cal. U Mo et al. PRL 90, 186403 (2003) Zhang et al. PRL 70, 1666 (1993) Incoherent part

  29. Calculation vs. Experiment | g > |f > 2p53d2 |D-Udc| 3d3L 2p53dL D |D*- Udc| 2p53d3C 3d3C D* 3d2 M. Taguchi et al. PRB 71,155102(2005)

  30. Hole- and Electron-Doped High-Tc Cuprates * M. van Veenendaal et al. PRB 49, 1407 (1994) * Ino et al., PRL 79, 2101 (1997) * Harima et al., PRB 64, 220507(R) (2001) * Steeneken et al. PRL 90, 247005 (2003) La2CuO4 Nd2CuO4

  31. Background（doping induced chemical potential shift) Mid-gap pinning scenario formation of new states within the band gap on doping Crossing the gap scenario M. van Veenendaal et al. PRB 49, 1407 (1994) m moves to the top of the valence band by hole-doping and bottom of the conduction band on electron-doping

  32. Calculation vs. Experiment | g > | f > 2p53d9 3d10L |D-Udc| 2p53d10L D |D*- Udc| 3d10C D* 2p53d10C 3d9 M. Taguchi et al. Phys. Rev. Lett. 95, 17702 (2005).

  33. Cu 2p XPS (Estimated Parameters) NCCO LSCO UHB UHB D* D D E F E F D* O 2p band O 2p band

  34. Charge-Transfer type UH D* D E F U O 2p band LH CT type system: Nd1.85Ce0.15CuO4 (NCCO) M. Taguchi et al., Phys. Rev. Lett. 95, 17702 (2005). 5.9keV 1.5keV See also G. Panaccione et al. PRB 77, 125133 (2008)

  35. 5950eV 800eV 43eV Valence Transition of YbInCu4 H. Sato et al., Phys. Rev. Lett., 93, 246404 (2004) See also Suga et al., J. Phys. Soc. Jpn, 78, 074704 (2009)

  36. e- hn q YbS: Ionic crystal Yb2+S2-, hence typical Yb2+ system However, the Yb valence estimated by L-edge RIXS & XAS: ~2.08 K. Syassen, Physica B+C 139-140 (1986) 277. ~2.35 E. Annese et al., Phys. Rev. B 70 (2004) 075117. Combining HAXPES with optical spectroscopy Evidence for purely Yb2+ bulk state, Yb3+ surface state, and energy-loss satellite due to interband transitions optical reflectivity M. Matsunami et al., Phys. Rev. B, 78, 185118(2008)

  37. V3+(bulk) Remote hole-doping at an interface M. Takizawa et al., PRL. 102, 236401(2009) For LaAlO3/SrTiO3, see M. Sing et al. PRL 102, 176805 (2009)

  38. Science, 291, 854 (2001) • Electronic structure of the room temperature ferromagnet Co:TiO2 anatase

  39. Nature Materials 4,173(2005) Carriers : hydrogenic type

  40. Core level spectra Al Ka XPS J W Quilty et al PRL 96, 027202(2006) T. Ohtsuki et al PRL 106, 047602(2011)

  41. Valence band spectra CoO/Co metal J W Quilty et al PRL 96, 027202(2006)

  42. J. Woicik et al Phys. Rev. Lett. 89, 077401(2002)

  43. Co 2p-3d XAS

  44. Co 2p-3d Resonant PES

  45. Ti 2p-3d Resonant PES Coherent + Incoherent feature T. Ohtsuki et al PRL 106, 047602(2011)

  46. Surface Science, 601, 5034(2007) charge neutrality condition : Co2+ + VO2− + 2Ti 4+  Co 2+ + 2Ti 3+ (VO is oxygen vacancy)

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