ARPES studiesof magneticphases in parents of iron-basedsuperconductors

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1 ARPES studiesof magneticphases in parents of iron-basedsuperconductors Véronique Brouet, Ping-Hui Lin, Maria Fuglsang Jensen, Laboratoire de Physique des Solides d Orsay Amina Taleb-Ibrahimi, Patrick Le Fèvre, François Bertran CASSIOPEE beamline, SOLEIL synchrotron, France Dorothée Colson, Anne Forget, Florence Rullier-Albenque SPEC, CEA-Saclay, France : Sample synthesis Emilio Giannini University of Geneva, Switzerland: FeTe samples

2 A surprise in 2008 : ironbasedsuperconductors => 55K in Sm(O 1-x F x )FeAs Ren et al., Chinese Phys. Letters April 2008 Electron-phonon coupling is expected and calculated to be weak(λ=0,2)! L. Boeriet al., PRL 2008 Unconventional superconductivity? Magnetic pairing?? Similarto cuprates?

3 Outline - What can we learn about magnetism by studying the electronic structure? - How canwelearnabout the electronicstructure? => Angle Resolved PhotoElectron Spectroscopy(ARPES) - Itinerant or localized magnetism in iron pnictides? Almost all magnetic phases are metallic, but they are correlated and cannot be described by a simple spin density wave picture. => BaFe 2 As 2 (T N =140K) : the AF orderingcorresponds to good FS nesting => FeTe(T N =76K) : the AF orderingdoesnot correspond to FS nesting => CaCo 2 As 2 (T N =72K) : ferromagneticorderingin the planes => seeposter by J. Mansart

4 Whatcanwelearnabout magnetismby studyingthe electronicstructure? ~ M ~ M 2a

5 How can we learn about the electronic structure? ARPES : Angle Resolved PhotoElectron Spectroscopy Hole pockets hv Z θ e - Electron analyser X φ Crystal Y k y E = hν W kin E B hk = 2mEkin sinθ k x

6 How can we learn about the electronic structure? ARPES : Angle Resolved PhotoElectron Spectroscopy Electron pocket hv Z θ e - Electron analyser X φ Crystal Y k y E = hν W kin E B hk = 2mEkin sinθ k x

7 How can we learn about the electronic structure? Fermi Surface The Fermi Surface ismade out of smallholeand electronpocketsmade out of at least three different orbitals.

8 How can we learn about the electronic structure? q Band structure along diagonal q Γ X => Good nestingbetweenholeand electron pockets for q=(π, π) 6e - /Fe The Fermi Surface ismade out of smallholeand electronpocketsmade out of at least three different orbitals.

9 BaFe 2 As 2 : magneticorderat(π, π) q AF Neutrons Resistivity Q AF = (π,π) M = 0,87 µ B Τ Ν =150Κ Huang et al., PRL 2008

10 Localizedmagnetismpoint of view Magnetic ordering patterns can also be understood from localized picture Fe As J 2 Frustrated AF interactions : J 1 => Checkerboardfor J 1 > 2J 2 => Stripefor J 2 > J 1 /2 Yildirim, PRL2008

11 Fermi Surface in BaFe 2 As 2 acrosst mag Fermi Surface at 150K Fermi Surface at 20K «droplets» [de Jong, EPL10] M.F. Jensen, V. Brouet et al, PRB 2011

12 Nestingof holeand electronpocketsin Fermi Surface at 150K BaFe 2 As 2 Minor ellipse axis Gap from ARPES spectra 20K ~ 20meV q AF Major ellipse axis 20K 0 mev M.F. Jensen, V. Brouet et al, PRB 2011

13 Nestingof holeand electronpocketsin Fermi Surface at 20K BaFe 2 As 2 Minor ellipse axis Gap from ARPES spectra 20K ~ 20meV Major ellipse axis 20K 0 mev M.F. Jensen, V. Brouet et al, PRB 2011

14 Reconstruction beyondnesting Band move withrespect to PM state => Gaps and shifts of bands have a similar order of magnitude (20-30meV). They stabilize equally the AFM state. SeeM.D. Johannes and I.I. Mazin, PRB 2009 Detwinned experiment Yi, Shenet al., PNAS 2011 Orbital orderingbetweend xz and d yz Γ X Γ Y

15 MagneticorderinFeTe q AF FeTe Resistivity Τ Ν =72Κ Much larger magnetic moment => M=2,1µ B Bao, PRL 2009 Chen, PRB 2009

16 Localizedmagnetismpoint of view Magnetic ordering patterns can also be understood from localized picture J 2 Frustrated AF interactions : J 3 J 1 => Checkerboardfor J 1 > 2J 2 => Stripefor J 2 > J 1 /2 Yildirim, PRL2008 At high d v J 1 and J 2 decrease J 3 increase => Double stripe for J 3 >J 2 /2 Ma et al.,prl2009 Moon and Choi, PRL2010

17 Fermi Surface throughthe magnetic 80Κ transition Seealso: Zhang et al., PRB 2012 Liu et al., PRL Κ Differentevolutioncomparedto BaFe 2 As 2 : no «droplets»

18 Evolution of the different bands Γ odd/xz Energy (ev) Γ even/xz Μ odd/yz No foldedband, no gap opening Shift of somebands and changes in lineshapes P.H. Lin et al., to appearin Phys. Rev. Letters

19 «Pseudogap» on the electronpocket 80K - The pseudogapexplainsverywellthe «badmetallicbehavior» in the PM state. - It shows thatmagneticfluctuations are detrimental to metallicity «Hund smetals» : new type of correlations due to the interplay between local moment and itinerancy 20K P.H. Lin et al., to appearin Phys. Rev. Letters Fe 1 Fe 2 K. Hauleand G Kotliar, New J. of Phys L. demedici, Mravlje, Georges, PRL 2011

20 Conclusions => Very different reconstruction of the electronic structure are observed witharpes, wherenestingdoesnot playthe leadingrole. => The formation of magneticmoment ismostlya local effect, but the magnetic structure optimizes conducting channel. => New types of correlations emerge form this particular magnetic background.