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Quasiparticle Self-consistent GW Study of LSMO and future studies

Quasiparticle Self-consistent GW Study of LSMO and future studies. Hiori Kino. Half-metal: Important materials for spin-electronics Future targets: Semiconductor: Impurity problem Antiferromagnetic Mott insulators: positions of oxigen levels.

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Quasiparticle Self-consistent GW Study of LSMO and future studies

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  1. Quasiparticle Self-consistent GW Study of LSMO and future studies Hiori Kino Half-metal: Important materials for spin-electronics Future targets: Semiconductor: Impurity problem Antiferromagnetic Mott insulators: positions of oxigen levels

  2. GW method: first-principles (no parameter), correlation= RPA-level LDA GWA (RPA, without vertex correction) (use only the diagonal self-energy) + + + Bare Exchange and Correlated parts made of and

  3. QPscGWquasiparticle self-consistent GW one-body potential 1. Neglect frequency dependence of S(w) 2. DS=0, when self-consistency is achieved.

  4. Merits of QPscGW No Z factor, easy to analyze QP dispersion, full k-path ...

  5. Half-metal --- application DOS ↑ ↓ ↑ ↑ Half-metal ↓ EF ↓ Spin valve --- MRAM Spin OLED (organic light emitting diode) Applications

  6. I↑ ↓ ↓ ↑ ↑ EF EF I↑ Basic Idea too simple...

  7. e↑ Spin valve --- MRAM Alq=8-hydroxyquinoline aluminium -30% Xiong et al., Nature 427, 821 (2004).

  8. h↑ e↑ Spin OLED (organic light emitting diode)---Organic EL (electroluminescence) Change luminescence efficiency luminescence phosphorescence hn hn L+1 (slow) L T1 S0 S1 • Organic semiconductor • small Z: small LS coupling • long spin life time =0% semiconductor E.g. Davis and Bussmann, JAP 93, 7358 (2003).

  9. La0.7Sr0.3MnO3, (La0.7Ba0.3MnO3,La0.7Ca0.3MnO3) LaMnO3: collosal magnetoresistance oxides a strongly correlated system (intrinsic ramdomness) In theories LSDA: nonzero DOS at EFin minority spin component In experiments,many experiments: spin polarization: 35%-100% In this study, calculate La0.7Sr0.3MnO3 beyond LSDA. estimate a band gap in the GW approximation.

  10. Experimental results For the Minority spin state • Non-zero DOS at EF = partially spin-polarized • Andreev reflection, Soulen Jr. et al., • tunnel junction, Lu et al., Worledge et al., Sun et al., • residual resistivity, Nadgomy et al. (bulk) • Zero DOS at EF=fully spin-polarized • XPS, Park et al. • resistivity, Zhao et al. (bulk) • tunnel, Wei et al. (bulk)

  11. e.g. GW improves bandgaps Ionization energy L. Hedin, J. Phys. Condens. Matter 11,R489(1999)

  12. LMTO-ASA • virtual crystal approx. LSDA results of La0.7Ba0.3MnO3 La O Majority Mn eg <- Fermi level Minority Mn t2g <- Fermi level Mn Pm-3m La 4f Mn eg Mn eg Mn t2g Mn t2g Spin moment=3.55mB

  13. Majority spin fp-LMTO calculation La 4f More accurate dispersion at higher energies

  14. Double Hankel O3s fp-LMTO Minimum basis La7s O3p La 5p(semicore) La6d Mn 5s Mn 5p Mn4d

  15. It looks that a gap opens in the minority band and spin is fully polarized. GW calculation 6x6x6 (20 irreducible) k-points, ~+100eV 1st iteration GW result Not easy to see what happens from the figure…

  16. QPscGW result GW calculation 6x6x6 (20 irreducible) k-points, ~+100eV Spin moment=3.70mB (fully polarized) Minority spin, conduction bottom-EF=+0.9eV (Previous result, conduction bottom-EF=+2eV) La 4f=+12eV, c.f., exp.(inverse photoemission) ~+8eV (Is screening insufficient?)

  17. Effects of Mn potential distribution due to random La/Ca distribution La 2/3 Ca 1/3 • La2/3Ca1/3MnO3 • LSDA • random distribution of La/Ca • Mn potential distribution =0.6eV GW+randomness Mn eg Mn t2g Mn eg 0.3eV Mn t2g Pickett and Singh, PRB 55, 8642 (1997) O2p • 0.9eV(GW minority-spin band edge)-0.3eV(Mn potential distribution)=+0.3eV •  • no QP state in the minority spin component at EF evenin the presence of disorder

  18. QPscGW, computational costs LSMO, 5 atoms, upto ~100eV(~100bands), 20 k-points, SR11000, 4CPU • 1 cycle • LDA and converting data to GW data ~1hr • exchange~15hr • polarization function ~8hr • correlation ~74hr • 1day for LDA+exchange+polarization (1 q4L job) • 1day for correlation (4 q4L jobs simultaneously) About 10 cycles to be converged ~20days (2.5 q4L jobs per day) Disk: ~10Gbyte

  19. Lambin & Vigneron, RPB 29, 3430 (1984) An example of diamond-Si GW Tetrahedron DOS Im(S) A(w) w k=(000) E+Re(S(w)) QP Phonon+photon=>plariton QP+plasmon=>plasmon+plasmaron? Plasmaron? plasmon LDA Z~0.75 LDA qpGW qpGW

  20. Future problems

  21. Impurity level of semiconductors donor acceptor Si Direct determination of acceptor and donor levels GW LDA orbital energyquasiparticle energy unoccupied energy level: underestimated

  22. Antiferromagnetic Mott insulators:positions of oxigen levels • In the AF Mott insulators, AF spin-up and -down bands corresponds to the upper and lower Hubbard bands. LDA GW M↓ M↓ M↑ ? O O M↑ Some improvement on the energy level of ogygen? Oxygen level is too low

  23. Next topic

  24. Complementing input files of fp-LMTO H. Kino and H. Kotani • fpLMTO is • fullpotential • efficient, fast, for bulk systems • We distribute the GW programs and would like to make it popular. • The present GW program strongly depends on the fpLMTO program. But, it is hard to write input files of fpLMTO. People do not use such a program.

  25. Interstitial region of fpLMTO wavefunctions potential Interstitial region is expanded via Hunkel functions, Parameters of Hunkel functions are necessary. But it is not easy for beginners of fpLMTO to give good values. What kind of values are optimal? E.g. plane wave ~ cutoff energy

  26. input files of fp-LMTO We made scripts to complement input files of fpLMTO Complement each section A minimum input file HEADER LSMO VERS LMF-6.10 LMASA-6.10 STRUC NBAS=5 NSPEC=3 NL=7 ALAT=7.3246 PLAT=1 0 0 0 1 0 0 0 1 SYMGRP find SPEC ATOM=Mn Z=25.0 R=2.05 LMX=6 quality=low ATOM=La Z=56.7 R=3.3 LMX=6 quality=gw1 ATOM=O Z= 8.0 R=1.6 LMX=6 MTOQ=s,s,0,0,0 LMX=4 A=0.015 SITE ATOM=Mn POS=0.0 0.0 0.0 ATOM=La POS=0.5 0.5 0.5 ATOM=O POS=0.5 0.0 0.0 ATOM=O POS=0.0 0.5 0.0 ATOM=O POS=0.0 0.0 0.5 HAM GMAX=11 SPEC ATOM= Mn Z= 25.0 R= 2.05 LMX= 6 LMXA= 4 KMXA= 3 A= 0.016 EH= -1.00 -1.00 -1.00 RSMH= 1.37 1.37 0.91 P= 4.59 4.35 3.88 4.17 5.10 IDMOD= 0 0 0 1 1 ATOM= La Z= 56.7 R= 3.3 LMX= 6 LMXA= 4 KMXA= 3 A= 0.016 EH= -1.00 -1.00 -1.00 -0.20 RSMH= 2.20 2.20 1.81 1.40 EH2= -0.20 -0.20 -0.20 RSMH2= 2.20 2.20 1.81 P= 6.57 6.21 5.85 4.13 5.13 IDMOD= 0 0 0 1 1 ATOM= O Z= 8.0 R= 1.6 LMX= 6LMX= 4 A= 0.015 EH= -1.30 -1.00 RSMH= 0.87 0.81 P= 2.88 2.85 3.26 4.13 5.09 IDMOD= 0 0 1 1 1 Keywords to control accuracy

  27. input files of fp-LMTO We made a prototype. Many tests are necessary to give better parameters!

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