Iron%20pnictides%20and%20calchogenides:%20a%20new%20class%20of%20strongly%20correlated%20metals

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Iron pnictides and calchogenides a new class of
strongly correlated metals

• Gabriel Kotliar
• Center for Materials Theory
• Rutgers University

RPMBT16
16th International Conference on Progress
in Many Body Theory Nov28-Dec 2nd (2011) San
Carlos de Bariloche Argentina
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References and Collaborators

• Itinerant or localized ? Quantify!
• Haule K, Shim J H and GK Phys. Rev. Lett. 100,
  226402 (2008)
• Origin of the correlations .
• K Haule and GK New Journal of Physics 11 (2009)
  025021
• Where is the spectral weight ?
• A. Kutepov K. Haule Savrasov and GK Phys. Rev. B
  82, 045105 (2010)
• Magnetic State Spin and orbital anisotropy
• Yin Z Haule K and GK Nature Physics 7, 294297
  (2011)
• Landscape of tetrahedrally coordinated d6
  materials.
• Yin Z Haule K and GK Nature Materials
  10,932935(2011)
• Neutron Scattering
• H Park K. Haule and G. K ,Phys. Rev. Lett. 107,
  137007 (2011)

Intermediate strength m/m3-5
Hunds Coupling Orbital Blocking
122 Uniformly spread no clear satellites
Spin and orbitals exchange opposite frequency
dept.
Ligand height nesting correlaton
Apparent anisotropy of the spin waves
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2008 superconductivity in LaFeAsO1-xFx
La O-- (LaO) ionic-insulating (FeAs)-
layers active block Atomic iron , Fe
3d6 4s2. As Atomic arsenic Ar 3d10 4s2 4p3
Fe d6 As--- p6 Doping with electrons
F, d7
Hosono et.a.., Tokyo, JACS (2008)
Address Predictive power of state of the art
methods
Predictive power of realistic DMFT and its
extensions, LDADMFT . .
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Paglione and Greene Nature Physics 6, 645(2010)
The space of Fe pnictide/chalcogenide materials
Is there physics common ot the tetrahedrally
coordinated Fe d6 layers ?
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K1-xFe2-2xSe2
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Iron Pnictides correlation strength ?

• LDA calculation. D. J Singh and M.H. Du Phys.
  Rev. Lett. 100, 237003 (2008), I. Mazin, M.
  Johannes and collaborators. Itinerant magnets.
  
• LDA should be corrected by long wavelength
  fluctuations effects. LDA overestimate of moment
  due to proximity to quantum critical point.
  Include fluctuating twin and antiphase domain
  boundaries.
• Haule K, Shim J H and Kotliar G Phys. Rev. Lett.
  100, 226402 (2008). Parent compounds
  correlated multiorbital bad semi-metals
  on the itninerant side of localization
  delocalization transition. m/m3-5). small
  crystal fields.
• Band theory should be supplemented by local
  correlations to capture local quantum
  fluctuations. LDADMFT extensions correlations
  are implemented via F0 F2 F4 applied to a set of
  orbitals (projector)
• Localized point of view, magnetic
  frustration. Q.Si and E.Abrahams Phys. Rev.
  Lett. 101, 076401. (2008).
• Extension of the t-J model to S2 multiorbital
  situation.

Different views suggest different theoretical
approaches. Different reference systems to think
about and compute the properties of materials.
Validity of the approaches as experimental
information becomes available ?
The jury is still out.
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Early DMFT predictions
Generic values of U , 4 ev, and J .9 ev ,
orbital built on a 4 ev window
Small X-field splittings
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Hunds metals not doped Mott insulators ,
Strength of correlations are due to Fe Hunds
rule J not to Hubbard U. K. Haule and G. Kotliar
cond-mat arXiv0805.0722 New Journal of Physics
11 (2009) 025021
Reduction of the impurity model, J-gtJ/N
Nevidomsky and Coleman PRL (2010)
Orbital Blocking low energy J diagonal in
orbial indices Yin Haule and Kotliar Nature
Physics ( 2011)
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Orbital blocking due to Hunds
Low energy Kondo-like Hamiltonian
N5
unless
Only diagonal Kondo couplng J
N6
N5
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Yin et. al Nature Materials 2011
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Optical Spectroscopy can be used to determine the
mass enhancement relative to the band theory mass
(LDA)
LDADMFT had predicted correlation effects m/m
.3 -.2 this WAS seen in OPTICS.

• M. M. Qazilbash et. al. Nature Physics 5, 647
  (2009)

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Freq. dep. U matrix applied to localized Fe d
orbital, (12 ev window) Well parametrized by F0
F2 F4
After the constrained RPA
But with the self consistent GW input and
adopting a local Orbiital rather than a band
perspective Kutepov et. al.
F0 49 eV, F2 64 eV and F4 43 eV., nc6.2
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DOS and valence histogram
There is transfer of spectral weight to high
energies, spectral weight is conserved. But the
DOS is featuresless no satellites, and resembles
the LDA! Strong Correlations without Hubbard
bands. Big difference between oxides and
pnictides important role of As.
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M. Moment Optics by LDADMFT
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Z. Yin, Khaule , G Kotliar, Nature Physics (2011).
Exp moment 0.87 µB
LDADMFT moment 0.9 LDA moment 2µB
Correct plasma ?p DMFT 1.6eV Exp
1.6eV LDA 2.6eV 3 peak structure
beyond SDW
Experiment W. Z. Hu, et al, PRL 101, 257005
(2008). Nakajima, M. et al. Phys. Rev. B 81,
104528 (2010).
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Anisotropy of the conductivity predicted.
b FM short
a AFM long
Z. Yin K. Haule and GK Nature Physics 7, 294-297
(2011)
Experiment M. Nakajima, ,S Uchida, PNAS 108,
12238 (2011) Dusca . I Fisher L DiGiorgi EPL
(2011)
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QUALITATIVE INSIGHTS a) Strongly Frequency
Dependent Spin and Orbital Exchange Splittingb)
Spin splitting large at high frequency like in
Fe, Lichtenstein Katsnelson and Kotliar PRLPhys.
Rev. Lett 87, 067205 (2001). . Orbital
splitting large at low frequency. c) Qualitative
difference between BaFe2As2 and Oxides.
Z. P. Yin, Khaule , G. Kotliar Nature Physics 7,
294-297 (2011)
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All families share the same FePn layers Fe d6,
similar bands What governs the variations
among the families ?
DSDW
SDW
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Yin Haule GK Nature Materials (2011)
distance
Overal trend consistent with Fe-As distance
Hybridization with pnictogen
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Kinetic frustration and FeTe
Effective low energy hoppings
usually larger, but not when pnictogen height
large!
Destructive interference leads to kinetic
frustration!
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Phys. Rev. B 84, 054544 (2011)
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Neutron spectroscopy with LDADMFT
Theory H. Park , K. Haule and GK PRL in press
Experiments L Harriger H. Luo M. Liu T. Perring
C Frost H. Ju M. Norman and Pengcheng Dai
arXiv1011.3771
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Needed absolute intensities
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Fluctuating moment by neutrons
Large fluctuating moment can not be explained by
a purely itinerant model- doping dependence
different than in localized model.
Understandable in the Hunds metal picture. and
localized nature.
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Open Issues

• Superconductivity. Does the nature of the normal
  state matter for the superconductivity
• Refine fermiology photoemission and optics in
  the magnetic state of the materials
• Effects non local corrections.
• Other systems, 5fs, 4ds

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Thanks!! Collaborators
upportAFOSR (MURI) NSF, DOE (BES)
Collaborators Kristjan Haule, Andrei Kutepov,
Zhiping Yin, Hyowon. Park