Electronic band structure of ferro-pnictide superconductors by xantolus

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									    Electronic band structure of
ferro-pnictide superconductors
                          (FPS)

                    Alexander Kordyuk
                IFW Dresden & IMP Kiev




                                 FPS'11
                 Zvenigorod, 03.10.2011
Authors and Collaborations

  S. V. Borisenko     A. N. Yaresko       A. Varykhalov
  D. V. Evtushinsky   D. S. Inosov        E. Rienks
  V. B. Zabolotnyy    A. V. Boris         R. Follath
  T. K. Kim           G. L. Sun
                      D. L. Sun
  I. Morozov          V. Hinkov           H. Q. Luo
  S. Aswartham        C. T. Lin           Z. S. Wang
  S. Wurmhel          B. Keimer           H. H. Wen
  G. Behr
  C. Hess
  R. Hübel
  A. Koitzsch
  M. Knupfer
  B. Büchner




                                      DFG Research Unit 538
                                        and priority program
                                                    SPP 1458
                 Plan

• ARPES on FPS

• Band structure of 111 and 122

• Which electrons do superconductivity

• ... and why?
         Photoelectric effect + electron analyser

          ARPES Image
energy




         angle / momentum
ARPES Image → ARPES Space
        Momentum-energy space

                                                                   EK
                                                                             ky
                                                                        kx
                           TiSe2



                      95
Kinetic energy (eV)




                      94


                      93


                      92


                      91

                                   -1 0   -5   0          5   10        15

                                               Momentum
Fermi surface (energy distribution) map

                      TiSe2    EK
                                          ky
                                    kx
         Surface vs Bulk

Bi2Se3
Iron-based superconductors




            Hai-Hu Wen and Shiliang Li, Annu. Rev. Condens.Matter Phys. 2011
Iron-based superconductors




   11
  FeSe     111      122
  FeTe   LiFeAs   BaFe2As2
                               1111
                             LaFeAsO


                             Paglione & Greene, Nat. Phys. (2010)
122: truncated square tiling

M       Г

    X



                     Z



            Z=
Band structure of 122 (BFA)




                              Yaresko 2010
Band structure of 122 (BFA)




                              Yaresko 2010
Band structure of FPS




                        Yaresko 2010
   Iron-based superconductors




      11
     FeSe     111      122
     FeTe   LiFeAs   BaFe2As2
                                  1111
                                LaFeAsO



ARPESable                       Paglione & Greene, Nat. Phys. (2010)
                                Phase diagrams




                                                                             H.Luetkens et al. Nature Mat. 2009
H.-H.Wen & S.Li Annu. Rev. Cond. Mat.          S.Nandi et al. PRL 2010
            Phys. 2011




N.Katayama et al. arXiv:1003.4525       Y.J.Yan et al. arXiv:1104.4941   Basov & Chubukov Nature Phys. 2011
                     Phase diagrams



                                                                 111




S.Jiang et al. J.Phys.Cond.Matt. 2009     X.C.Wang et al. High
                                        Pressure Research 2011
           111
LiFeAs (Tc = 18 K, non-magnetic)
NaFeAs (Tc = 9-26 K, TAF = 40 K)
        Perfectly ARPESable LiFeAs




1. Superconducting with Tc = 18 K but non-magnetic…
2. Stoichiometric = impurity clean.
3. Perfectly two-dimensional Fe-3dxy band well separated from
   other bands: easy to analyse its fine structure.
4. Cleaves between the two Li layers => non-polar surface.
LiFeAs: band structure




                         Borisenko PRL 2010
LiFeAs: band structure




        dxy
        dxz
        dyz




              Graser et al. New J. Phys. 2009
Three orbital model




                 P.A.Lee & X.-G.Wen PRB 2008
                                                LiFeAs: band structure
                           0.5



                                       LDA
Calculated energy (eV)
                           0.0
                           -0.5
Experimental energy (eV)
                           0.1
                           0.0




                                                           • 3 times renormalized;
                           -0.1




                                                           • dxy band is 60 (bare 180) meV higher:
                           -0.3 -0.2




                                                             no FS nesting;
                                                ARPES      • dxz/dyz bands are 40 (120) meV lower;
                                       Γ               X
                                                           • dxz/dyz bands are flattened or “pinned”
                                       In-plane momentum
                                                             to the Fermi level.
                                                                                              Borisenko PRL 2010
                                                                                                    Yaresko 2010
LiFeAs: renormalization




                λ = λel + λph = 2 + 1.38
                                 Kordyuk PRB 2010
LiFeAs: FS orbital character


                               dxy
                               dxz
                               dyz
               122
             hole doped
BaFe2As2 (BFA) ▪ Ba1-xKxFe2As2 (BKFA) ▪ KFA
          Ba1-xNaxFe2As2 (BNFA)
        122
   electron doped
BFA ▪ Ba(Fe1-xCox )2As2 (BFCA)
    122
isovalent doping
BaFe2(As1-xPx )2 (BFAP)




                   H. Shishido et al. PRL 2010
                  Fermi surface of BKFA




Mazin & Schmalian 2009

                                                         Ding EPL 2008




Tesanovic Physics 2009   Shimojima Science 2011   Hu & Ding arXiv:1107.1334
Fermi surface of BKFA
Fermi surface of BKFA




               V. Zabolotnyy Nature 2009, Phys C 2009
V. Zabolotnyy Nature 2009, Phys C 2009
             Propeller FS in 122

  Ba(Fe1-xCox )2As2       Ba1-xKxFe2As2       Ba1-xNaxFe2As2
ω = –90 meV, hv = 80 eV   ω = 0, hv = 80 eV    ω = 0, hv = 80 eV




                                                   Evtushinsky 2010
Calculated FC of BFA - BKFA          Г      M




                          Yaresko, Zabolotnyy 2011
BKFA: exp & calc




                   Yaresko, Zabolotnyy 2011
    Calculated BFA band structure
     renormalized and shifted by 76 meV




Г    X   Г   T   P   T   M   X   M
                                     Yaresko, Zabolotnyy 2011
dxz + dyz




dxy




            Yaresko 2010
                        Experimental energy (eV)          Calculated energy (eV)
                        -0.3 -0.2   -0.1   0.0   0.1          -0.5     0.0     0.5




                    Γ
                                                                             LDA




                                                  ARPES




In-plane momentum
                    X
                                                                                     BKFA: band structure
BKFA: Fermi surface and gaps




                        D. Evtushinsky PRB 2009, NJP 2009


   dxy
           Δ correlates with the orbital composition:
   dxz
            Δ = 3–4 meV for 3dxy and 3dz2
   dyz      Δ = 10.5 meV for 3dxz/yz.

                                       D. Evtushinsky 2011
BFAP: node or small gap?




                    Y. Zhang et al. arXiv:1109.0229
KFA: hole-like Fermi surfaces




                     T. Yoshida et al. arXiv:1007.2698v2
FS‘s of iron-based superconductors




                             D. Evtushinsky 2011
FS‘s of iron-based superconductors




                             D. Evtushinsky 2011
             BFA: density of states
                                                    AxFe2Se2 (31K)




                                   BFCA (26K)
                                   LiFeAs (18K)
DOS




                             BFA




      -0.2    -0.1          0                 0.1              0.2
                     Binding energy (eV)
             BFA: density of states
                                                    AxFe2Se2 (31K)
                             BKFA (38K)


                                   BFCA (26K)
                                   LiFeAs (18K)
DOS




                             BFA




      -0.2    -0.1          0                 0.1              0.2
                     Binding energy (eV)
Tc(density of states)?




                  Sadovskii, Kuchinskii, Nekrasov 2011
                      BFA: density of states
                                                                  AxFe2Se2 (31K)
                                           BKFA (38K)
      Hole doped KFA


                                                 BFCA (26K)
                                                 LiFeAs (18K)
DOS




                                           BFA


             KFA (4K) ???

      -0.2                  -0.1          0                 0.1              0.2
                                   Binding energy (eV)
Generalized phase diagram
              140




                                                                 Ba(Fe1-xCox )2As2
              120

              100




                                                                                     KxFe2-ySe2
Temperature

              80
                                  Ba1-xKxFe2As2
              60

              40      KFe2As2                         SDW
              20
                                         SC                     SC                   SC
               0
                    -0.5   -0.4    -0.3    -0.2    -0.1      0    0.1
                                      Extra electrons per Fe atom




                      dxz + dyz




                            KFA            BKFA           BFCA                               KFS
SC & SDW




           Kopaev & Rusinov Phys. Let. A 1987…
SC & SDW




           Kopaev & Rusinov Phys. Let. A 1987…
SC & SDW




           Yaresko 2011
                 Conclusions
• The band structure of Fe-SC is well captured by LDA
  but do not take it too literally. The calculated Fermi
  surface is usually bad starting point for theory.
• Main contributors to SC are dxz,yz electrons and Tc
  for different compounds seems to correlate with the
  position of the Van Hove singuliarities (Lifshitz
  transitions) for the xz- and yz-bands.
• Both the renormalization and SDW do increase the
  DOS at the Fermi level for dxz,yz- electrons.
THANK YOU

								
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