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The 7 th Day After First Light

The 7 th Day After First Light. Yu He SC Meeting Jul 25, 2013. Milestones. Early Guinea Pigs. Metal Cuprate Topological Insulator Pnictide FeSe Film. PROBLEMS!. The Laser. Ionization Chamber (IC-P). Gas Conversion Module (GCM). ARPES Manifold. Dispersion Chamber (DC).

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The 7 th Day After First Light

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  1. The 7th Day After First Light Yu He SC Meeting Jul 25, 2013 • Milestones • Early Guinea Pigs Metal Cuprate Topological Insulator Pnictide FeSe Film • PROBLEMS!

  2. The Laser Ionization Chamber (IC-P) Gas Conversion Module (GCM) ARPES Manifold Dispersion Chamber (DC) Amplifier, SHG and FHG Gas Control Panel (GCP) Seed laser, 100MHz, IR

  3. Milestones Jul 10 Jul 16 Jul 12 Jul 07 Jul 20 Jul 11 Jul 15

  4. The ‘Gold’ Standard By proper beam alignment, two step puzzle solved Best Au resolution ~10meV

  5. UD92 Bi2212 – half wave plate rotation • Polarization changes intensity by 2 folds • Signal-background ratio modulated • To be motorized • To add quarter-wave plate

  6. UD92 Bi2212 – reaching zone boundary • Reaching zone boundary! • Need better stats and even longer time per scan

  7. Bi2Se3 – characterize polarization?

  8. Bi2Se3 – linear dichroism -0.1eV 0 eV Z.-H. Zhu et al, PRL 110, 216401 (2013) 0.1eV • P-polarization dominates • What exactly is the half-wave plate doing to the linear polarization of 11eV? 0.2eV

  9. Bi2Se3 – Bi2Se3 – circular dichroism 0.1eV 0.2eV Z.-H. Zhu et al, PRL 110, 216401 (2013)

  10. Bi2Se3 – Bi2Se3 – circular dichroism 0.1eV 0.2eV • Small circular dichroism exists • Linear dichroism dominates • Rotating half wave plate by θ doesn’t simply rotate linear polarization by 2θ Z.-H. Zhu et al, PRL 110, 216401 (2013)

  11. FeTeSe – blur band and space charging UV power 411uW 334uW 223uW 140uW

  12. FeTeSe – blur band and space charging • Strong evidence for space charging • Down to 150k counts/second at EF the effect is still visible • What’s wrong?

  13. FeSe film – reaching zone boundary M Γ Γ 18K hv = 10.897eV 1024nm+256nm+256nm hv = 21.218eV Helium plasma discharge

  14. FeSe film – reaching zone boundary • Back bending clearly observed below Tc • Less background at low binding energy • Fully reaching zone boundary – powerful tool to study fine structures and subtle changes at M point

  15. Problems! Space Charging • Increase rep rate to 10MHz or more • The limiting factor: power or spot size? • Pass energy to get around? • How keen are we now perusing 100uW power? Polarization • Motorize • What does the wave plate exactly do upstream the GCM? • Quarter wave plate for circular dichroism Resolution • Go beyond 10meV how about 1meV?

  16. The END

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