Zhiping Yin - mcc.uiuc. · PDF filea magnetic field Problem of a quantum impurity (atom in a...
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DFT+DMFT to Correlated Electronic Structures: Recent Developments and Applications to
Iron-based Superconductors
Zhiping Yin
Department of Physics, Rutgers University
Collaborators: G. Kotliar, K. Haule
Electronic Structures 2013, Williamsburg, VA, June 11-14, 2013
(Some unpublished results were removed from the slides. Interested readers can contact the author via email yinzping at physics.rutgers.edu for details.)
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Acknowledgements
• Gabriel Kotliar, Kristjan Haule, Warren Pickett
• Hyowon Park, Jan Tomczak, and other group members (Rutgers)
• Girsh Blumberg (Rutgers)
• Pengcheng Dai (UTK)
• Meigan Aronson (Stony Brook, BNL)
• NSF and AFOSR for $upport
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• Summary
• Applications of DFT+DMFT to FeSCs
SpectroscopySusceptibilitySuperconductivityResonant Raman, Thermoelectric
• Features of our implementation of DFT+DMFT
• DMFT and DFT+DMFT in a nutshell
Outline
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Dynamic Mean Field Theory (DMFT) in a nutshell
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Weiss mean field theory for spin systems
Exact in the limit of large z
Classical problem of spin ina magnetic field Problem of a quantum impurity (atom in a fermionic band)
Space fluctuations are ignored, time fluctuations are treated exactly
Dynamical mean field theory (DMFT) for the electronic problem
exact in the limit of large z
(G. Kotliar, S. Savrasov, K.Haule, V. Oudovenko, O. Parcollet, and C. Marianetti, RMP 78, 865-951 2006).
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DFT+DMFT
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Impurity Lattice
K. Haule et al, Phys. Rev. B 81, 195107 (2010).
Charge self-consistent implementation ,avoids construction of low energy models
DFT (WIEN2k)
DMFT(CTQMC)
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Features• Valence histogram, self-energy, Green’s function• ARPES• Optical conductivity• Non-colinear magnetism with spin-orbit coupling (non-
perturbative)• Thermoelectric power coefficient using proper dipole
transition matrix element (unlike Boltztrap and BoltzWann: Peierls appr., no phase factors)
• Local and momentum dependent spin and charge susceptibility including two-particle vertex corrections
• Superconducting gap symmetry and coupling strength including vertex corrections (available soon)
• Resonant Raman spectra (in progress)
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Fmax 26CT K
26 K
The iron-based superconductors
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First discovery in 2008: LaFeAsO1-xFx, H. Hosono, JACS 130, 3296 (2/13/2008).
H. Hosono
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The diversity of FeSC’s
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J. Paglione and R L. Greene, Nature Physics 6, 645-658 (2010).
KxFe2-ySe2
+K
M. R. Norman, Physics 1, 21 (2008).
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Thin film FeSe
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All FeSCs share the same FePn layer, but there are large variations among them.
SDWDSDW
Mass enhancement in the PM phase. Magnetic moment in the ordered phases.
Can DFT+DMFT account for these variations without tuning U and J?
ZPY, K. Haule and G. Kotliar, Nature Materials 10, 932 (2011).
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Moments and Magnetism
Moments by DFT are around 2 , overestimated by a factor of two (ZPY et al, PRL 101, 047001 (2008).)
Moments by DFT+DMFT are in good agreement with experiments
FeTe: 2.03, W. Bao et al., PRL 102, 247001 (2009). NaFeAs: 0.31, L. Ma et al., PRB 83, 132501 (2011).
Ba122: 0.87, Q. Huang et al., PRL 101, 257003 (2008).LaFeAsO: 0.82, H.-F. Li et al., PRB 82, 064409 (2010).CaFeAsF: 0.49, Y. Xiao et al., PRB 79, 060504(R) (2009).SrFeAsF: 0.58, Y. Xiao et al., PRB 81, 094523 (2010).
Sr122: 0.94, J. Zhao et al., PRB 78, 140504(R) (2008).Ca122: 0.80, A. I. Goldman et al., PRB 78, 100506(R) (2008).
Experimental moment ( ):
TheoryZPY, K. Haule and G. Kotliar, Nature Materials 10, 932 (2011).
B
B
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Mass enhancement
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ZPY, K. Haule and G. Kotliar, Nature Materials 10, 932 (2011). DFT+DMFT accounts for the variations in all families
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Valence Histogram
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ZPY, K. Haule and G. Kotliar, Nature Materials 10, 932 (2011).
LaMnPO
J. W. Simonson, ZPY et al., PNAS 109, E1815-E1819 (2012).
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Self-energy: Fractional power-law behavior in some FeSC’s
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Experiments Theory (DFT+DMFT)
1 '' ' '
1( ) Re[ ]
( ) ( ) ( 0)i
1( ) ~
''( )
ZPY et al., PRB 86, 195141 (2012). is orbital and material dependent, not necessarily 1/2.
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T-dependence: Coherence-incoherence crossover
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Theory: ZPY et al., PRB 86, 195141 (2012). Experiments: M. Yi et al., PRL 101, 067003 (2013).
2 2x yK Fe SeFeTe
Very low coherence temperature
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Experiments: W. Z. Hu, et al, PRL 101, 257005 (2008).Nakajima, M. et al. Phys. Rev. B 81, 104528 (2010).
PM statebroader Drude peak
Correct plasma ωp:
DMFT ~ 1.6eVExp ~ 1.6eVLDA ~ 2.6eV
SDW state more coherentsharper Drude peak
Above SDW gap: 3 peaks
ZPY, K. Haule, G. Kotliar, Nature Physics 7, 294 (2011).
Optical conductivity: BaFe2As2
Good agreement at low energy in both paramagnetic and magnetic phases
SDW gap
BaFe2As2
Magnetic moment:Exp. : 0.87 DMFT: 0.9LSDA: 2.0
B
B
B
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Optical in-plane anisotropy predicted by DFT+DMFT
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First two excitations only in AFM x-direction
Larger SDW gap in FM y-direction
BaFe2As2 in the SDW phaseDMFT prediction:Nature Physics 7, 294 (04/2011),arXiv:1007.2867 (07/2010).
Experiment:M. Nakajima, …,S Uchida,PNAS 108, 12238 (07/2011), arXiv: 1106.4967 (06/2011).
1
23
1
23
AFM (x) direction
FM(y
) d
irec
tio
n
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Susceptibility with vertex correction
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One particle Green’s function
Sampled by ctqmc
Bethe-Salpeter equation:
H. Park et al., PRL 107, 137007 (2011).Easily replaced with charge or orbital to obtain charge or orbital susceptibility
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Spin susceptibility in iron pnictides
Theory and Experiments: M. Liu et al., Nature Physics 8, 376-381 (2012), M. Wang et al, arXiv:1303.7339
PM BaFe2As2
Theory: H. Park et al., PRL 107, 137007 (2011).Experiments: L. W. Harriger et al, PRB 84, 054544 (2011)
Theory
Experiment
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Superconductivity
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H. Park, Ph.D thesis, Rutgers University (2011).
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Superconductivity
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H. Park, Ph.D thesis, Rutgers University (2011).
Leading eigenvalueapproaches 1 gives Tc
The corresponding eigenfunction gives the pairing symmetry
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Superconductivity: pairing symmetry
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Orbital space Band space: on FS
S+-
d-wave
Ground State
First Excited State
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Raman susceptibility
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Experimental data from V. K. Thorsmolle and G. Blumberg (Rutgers University)
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Thermoelectric Power: FeSi
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J. M. Tomczak, K. Haule and G. Kotliar, PNAS 109 (9), 3243-3246 (2012)
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Summary
• DFT+DMFT is shown to capture quantitatively many experimental observables in the correlated iron-based superconductors.
• DFT+DMFT is a promising tool to study correlated materials and can be used, in collaborations with experiments, to rationally design novel correlated functional materials with desirable properties such as high temperature superconductivity and large thermoelectric power.
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