Page 1
Kinks in the dispersion of strongly correlatedelectrons
Krzysztof Byczuk
Institute of Physics, EKM, Augsburg University, Germany
April 20th, 2007
K. Byczuk, M. Kollar, K. Held, Y.-F. Yang, I.A. Nekrasov, Th. Pruschke, D. VollhardtNature Physics 3, 168 (2007)
Page 2
Collaboration M. Kollar, D. Vollhardt, Augsburg, Germany
K. Held, Y.-F. Yang, Stuttgart, Germany
I. Nekrasov, Ekaterinburg, Russia
T. Pruschke, Gottingen, Germany
Support from SFB 484
Page 3
Standard model of quantum many-body system
E(k)
k
quasiparticlequasiholeholonspinonplasmonmagnonphononpolaritonexcitonanyong-on...
emergent particles
(i) well defined dispersion relation
(ii) long (infinite) life-time
(iii) proper set of quantum numbers
(iv) statistics
Page 4
Dispersions and kinks
Coupling/hybridization
between different particles/modes
E(k)
k
E(k)
k
Df. kinks are abrupt slope changes in the dispersion relations
anticrossing, lifting degeneracy, ...
Provide information on modes and couplings
Page 5
Dispersions and kinks - coupling to bosons
E(k)
electron
k
boson
energy of a kink is related to energy of a bosonic fluctuation
Page 6
Dispersion of correlated electrons
One-particle spectral function - excitations at and
Dispersion relation
Dispersion relation is experimentally measured
Page 7
Angular Resolved Photoemission Spectroscopy
;
<
=KY
H
I
T
(OHFWURQ
HQHUJ\DQDO\]HU
&U\VWDO
k
k
k
k
1
2
3
4
Energy
Inte
nsity
energy distribution curve (EDC)
Inte
nsity
Momentum
E
E
E
E
1
2
3
4
momentum distribution curve (MDC)
energy resolution 1meV
Page 8
ARPES and graphene
Dirac linear dispersion relation for graphene
cond-mat/0608069
Page 9
Kinks in HTC
Kinks at meV
electron-phonon or electron-spin fluctuations coupling
cond-mat/0604284
Page 10
“Waterfalls” in HTC
different HTC systems, cond-mat/0607319
Kinks seen experimentally between 300-800 meVOrigin: phonos, spin fluctuations, not known yet
Page 11
Kinks orbital selective
π
γ β
π π π
α π
π
π
Γ
Χαβ
γ
Sr RuO , cond-mat/0508312
Kink at 30meV in -band only
Page 12
More examples of kinks in ARPES
SrVO
, cond-mat/0504075
Kinks seen experimentally at 150 meVPure electronic origin?
Page 13
Kinks in LDA+DMFT study of SrVO
plain band model with local correlations, no other bosons, ... but kinks!
≥21.510.50-0.5-1-1.5≤-2
ener
gy [e
V]
RΓXMΓ
-1
-0.5
0
0.5
1
1.5
log A(k,ω) [1/eV]
0.60.40.2
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
-5 -4 -3 -2 -1 0 1 2 3 4 5 6 7Energy, eV
-6
-5
-4
-3
-2
-1
0
1
2
Σ(ω
), eV
Real partImaginary part
-0.5 0 0.5
Energy, eV
-0.5
0
0.5
ReΣ
(ω),
eVSrVO3
LDA+DMFT(QMC) self-energy
V3d(t2g
) orbitals
I.A. Nekrasov et al., cond-mat/0508313, PRB (2006)
Not found in SIAM with simple hybridization function! DMFT self-consistency effect
Page 14
New purely electronic mechanism in strongly correlated systems
characteristic energy scale
range of validity for Fermi liquid theory
Page 15
Hubbard model for strongly correlated electrons
t
U
t
! !! !! ! " "" "" "# ## ## #
$ $$ $$ $% %% %% % & && && &' '' '' ' ( (( (( () )) )) ) * ** ** *+ ++ ++ +
, ,, ,, ,- -- -- - . .. .. ./ // // / 0 00 00 01 11 11 1 2 22 22 23 33 33 34 44 44 45 55 55 5
67676767676767676767676
87878787878787878787878
979797979797979797979
:7:7:7:7:7:7:7:7:7:7:
; ;; ;; ;; ;< << << << < = == == == => >> >> >> > ? ?? ?? ?? ?@ @@ @@ @@ @ A AA AA AA AB BB BB BB B
InIn
Out
TIME
DC DC E DC DC F
Local Hubbard physics
Page 16
All what we know about Hubbard model
Solved in limit (non-interacting limit)
Dispersion relation
Spectral function - one-particle excitations
Density of states (DOS) - thermodynamics
k
ω
A(k, )ω
ω
ωN( )
Page 17
All what we know about Hubbard model
Solved in limit (atomic limit)
Real self-energy
Spectral function
Green function and self-energy are local,i.e. independent
k
ω
A(k, )ω
ω
ωN( )LHB UHB
U
U
Page 18
Weakly correlated system
≥210-1-2≤-3
ener
gy [e
V]
RΓXMΓ
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
log A(k,ω) [1/eV]
Fermi liquid : for
for
Page 19
Kinks due to strong correlations
≥10.50-0.5-1-1.5≤-2
ener
gy [e
V]
RΓXMΓ
-0.2
-0.1
0
0.1
0.2
log A(k,ω) [1/eV]
0.60.4
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
ω qp
U
Ω
Fermi liquid : for
Different renormalization : for
Page 20
Mathematical explanation of kinks within DMFT
DMFT self-consistency condition
Three-peak structure sufficient condition
Fermi-liquid for
Page 21
Microscopic predictions
Starting from:
- bare dispersion relation
we predict that:
Page 22
Microscopic predictions Kink position
Intermediate energy regime
Change in the slope interaction independent
Curvature of the kink
Sharpness of the kink
Sharper for stronger
Page 23
Outlook: possible origin of the “waterfalls”
“Waterfalls”: kinks at ω? ≈ 300-400 meV in cuprates
• crossover to Hubbard bands? Wang et al. (2006)
• U t ⇒ dispersion goes from central peak to Hubbard bandK. Byczuk, M. Kollar (unpublished)
Σ(ω) = Σ0 +Σ1
ω+O
(1
ω2
)
⇓
EUHB,LHBk
≈1
2
[εk ±
√ε2
k+ cU2
] -2 -1.5 -1 -0.5 0 0.5 10
2
4
6
8
10U=8t=2, n=0.79
-2 -1.5 -1 -0.5 0 0.5 10
2
4
6
(0,0)-(0,π)
(0,0)-(π,π)
(0,π)
(0,0)
(π,π)
(0,0)
Page 24
Crossover to Hubbard bands
Hubbard model, square lattice, DMFT(NRG), U = 8t, n = 0.79
• ImΣ decays faster than ReΣ
• for large energies: Ek approaches EUHB,LHBk
• waterfalls from central peak to LHBK. Byczuk, M. Kollar (unpublished)Y.-F. Yang, K. Held (unpublished)
Page 25
Conclusions Strong correlations (three peak spectral function) a sufficient condition for
electronic kinks
Energy scale for electronic kinks determined by Fermi-liquidrenormalization and bare (LDA) density of states
sets the energy scale for Fermi-liquid regime where for
Beyond Fermi-liquid regime the dispersion is still renormalized and useful
for where the offset and determined by
and
Electronic kinks are within cluster extension of DMFT (DCA)
Electronic kinks and waterfalls are generic feature of strongly correlatedsystems