1 / 38

Xi Dai Institute of Physics(IOP), CAS Beijing, China

UC Davis conference on electronic structure, June. 2009. LDA+Gutzwiller Method for Correlated Electron Systems: Formalism and Its Application to Iron pnictides. Xi Dai Institute of Physics(IOP), CAS Beijing, China. Collabrators: X.Y. Deng, G. T. Wang, G. Xu, H. J. Zhang

afia
Download Presentation

Xi Dai Institute of Physics(IOP), CAS Beijing, China

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. UC Davis conference on electronic structure, June. 2009 LDA+Gutzwiller Method for Correlated Electron Systems:Formalism and Its Application to Iron pnictides Xi Dai Institute of Physics(IOP), CAS Beijing, China Collabrators: X.Y. Deng, G. T. Wang, G. Xu, H. J. Zhang Zhong Fang (IOP)

  2. Contents • Introduction to Gutzwiller density functional theory. • (Problems of LDA) • 2. LDA+Gutzwiller Method • Applications: Iron Pnictides • conclusions

  3. The Kohn-Sham local density approximation KS ansatz: Takea non-interacting system as reference

  4. Using local density approximation in GDFT Generalized KS ansatz: Gutzwiller DFT Takea system with on-site interaction as reference H=HLDA+HU-EDC

  5. Gutzwiller wave-function for multi-orbital system Γ: many body configurations on a single site. Single band: 22=4 N-band: 22n

  6. Gutzwiller Approximation: Generalizing to Multi-orbital

  7. Bench mark Gutzwiller Aproximation on two-band Hubbard model with DMFT+ED Gutzwiller Vs DMFT

  8. The flow chart of LDA+G

  9. Insufficiency of LDA for TMOs Insulator with Long-range ordering Correlated-Metal or MIT critical point Metal Ueff LDA+DMFT LDA+G LDA GGA LDA+U

  10. Example-1: Ground state of Fe LDA+G GGA LDA Deng, DX and FZ， EPL （2008） J. H. Cho and M. Scheffler, PRB (1996)

  11. Example-2: DFT results for Ni LDA Exp. • 30% wider • X point problem LDA＋G

  12. Example-3: NaCoO2 LDA D.J. Singh, PRB (2000) ARPES M.Z.Hasan, PRL (2004) LDA+G Wang, DX, FZ PRL (2008)

  13. LDA+G covers: From Weakly correlated metals to Strongly corrlated insulators (ordered state) If q=1: HF limit is recovered (LDA+U) If 0<q<1: Kinetic renormalization included Same as DMFT for ground state! Much cheaper than DMFT ! 5 orbitals can be solved by 1-min on PC. PRL (2008) for NaCoO2; EPL (2008) for details

  14. Correlation In Iron Pnictides Crucial LaOFeAs: Ueff=3~4eV, JH=0.6~1.0eV Orbital fluctuation enhanced La2CuO4 Ueff Itinerant metal MIT Large U limit LDA & GGA LDA+U LDA+DMFT (High T) LDA+G (T=0K) Two questions: 1. Fe-As distance? 2. SDW state and Magnetic moment?

  15. Structure: Building-block FeAs-layer

  16. Structure: Mainly 4 types LaOFeAs (1111) BaFe2As2 (122) LixFeAs FeSe

  17. Basic Electronic Structure: LaOFeAs Energy (eV) Fe-3d As-4p O-2p A Γ X M Γ Z R A Z LDA

  18. Basic Electronic Structure: LaOFeAs Important: 5 orbitals/Fe are all involved Fe2+: nd=6

  19. Basic Electronic Structure: LaOFeAs FS Strong anisotropy Phonon Weak e-p coupling D. J. Singh & M. H. Du, PRL (2008).

  20. Success of LDA & GGA Magnetic Phase Diagram of LaOMAs: LaOMnAs: AF1 Semiconductor LaOCoAs: FM Metal Magnetic instabilities?? G. Xu, et.al., EPL, 82, 67002 (2008)

  21. Success of LDA & GGA LaOFeAs: Fermi surface Nesting J. Dong, et.al., EPL, 83, 27006 (2008)

  22. Success of LDA & GGA LaOFeAs: Stripe-type SDW (AF2) J. Dong, et.al., EPL, (2008). P. Dai, et.al., NATURE, (2008)

  23. Exp: Competing Orders X.H.Chen, et.al., Cond-mat/0807.3950 P. Dai’s neutron

  24. Basic Understanding from pure LDA: From LDA or GGA: 1. Multi-orbital nature (Orbital DOF) 2. Magnetic instabilities (Spin DOF) 3. Lattice coupled to M (Lattice DOF) Competing Orders is the Key!!! Problems: 1. Spin: moment? SDW? 2. Orbital: selective? 3. Lattice: Fe-As distance?phonon?

  25. Problems of LDA or GGA Problem (1): Fe-As position and bonding strength T. Fukuda, et. Al., arXiv:0808.0838 (cond-mat/0804.3355)

  26. Problems of LDA or GGA Problem (2): The band width found by ARPES is 50% Narrower H. Ding et al, Unpublished

  27. Problem of LDA & GGA: Problem (3): Magnetic Solution & Moment SDW M = 0.3~0.4 μB From exp. Spatial or On-site Fluctuation? T. Yildirim., et.al., (cond-mat/0804.2252)

  28. Other evidence of strong correlation effects in Iron Pnictides • Large Specific heat coefficient in FeTe (arXiv:0811.1489) • Incoherent spectral weight in optical conductivity • (N.L. Wang et al, unpublished) • Satellite peaks in core level spectra(H. Ding et al unpublished)

  29. LDA+G study for LaOFeAs: As position J is crucial !!

  30. LDA+G study for LaOFeP: As position

  31. LDA+G study for LaOFeAs: band-narrowing Renormalization: about factor of 2 consistent with ARPES

  32. LDA+G study for LaOFeAs: band-narrowing A  X M  Z R A Z

  33. LDA+G study for LaOFeAs: Crystal field is suppressed! Orbital Fluctuation is enhanced! This explains why J is crucial!

  34. The appearance of 3D FS LaOF0.1Fe0.9As Ba0.6K0.4Fe2As2

  35. The anisotropy in resistivity calculated by LDA+G

  36. Conclusions: Conclusions: U = 3 ~ 4 eV J = 0.6 ~1 eV  Crucial • Fe-As distance solved! • LaOFeAs, LaOFeP, BaFe2As2 • 2. Phonon frequency is soften by 30% • 3. Band-width renormalization • factor of 2, orbital fluctuation • 4. 3D FS, small anisotropy

  37. Thank you !

More Related