introduction to the electron phonon renormalization of the electronic band structure
TRANSCRIPT
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Elena CannucciaInstitut Laue-Langevin, Grenoble (France)
Introduction to the electron Introduction to the electron phonon renormalization of phonon renormalization of electronic band structureelectronic band structure
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The N particles The N particles world: world:
ionsions and and electronelectronss all togetherall together
Electron phonon renormalizationElectron phonon renormalization of electronic band structure of electronic band structure
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Born–Oppenheimer approximation Born–Oppenheimer approximation
a perturbative approacha perturbative approach
Electron phonon at workElectron phonon at work
beyond the beyond the Born–Oppenheimer approximationBorn–Oppenheimer approximation
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The separated worlds of The separated worlds of phononsphonons and electron and electronss
Electrons live in the bands generated by the ionic potential
Phonons are the quantizedionic vibrations on the potential
generated by the electrons
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Born–Oppenheimer approximation Born–Oppenheimer approximation
a perturbative approacha perturbative approach
Electron phonon at workElectron phonon at work
beyond the beyond the Born–Oppenheimer approximationBorn–Oppenheimer approximation
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Coupling electrons and phonons …Coupling electrons and phonons …Superconductivity Joule's heating
Electron relaxation(luminescence)
Polaronic transport Coherent PhononsPeierls instability
Raman Spectroscopyetc......
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EPC on the electronic structureEPC on the electronic structure
Kink in the band structure Mass Enhancement
Temperature dependence of band gaps
A. Marini, PRL 101,106405 (2008)
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Energy levels renormalizationEnergy levels renormalization
Thermal Thermal expansionexpansion
Electron-Phonon Electron-Phonon interactioninteraction
P.B. Allen and M. Cardona Phys. Rev. B 27 4760 (1983)
>>
Where does the coupling come from?
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Born–Oppenheimer approximation Born–Oppenheimer approximation
a perturbative approacha perturbative approach
Electron phonon at workElectron phonon at work
beyond the beyond the Born–Oppenheimer approximationBorn–Oppenheimer approximation
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A perturbative approach:A perturbative approach:Heine-Allen-Cardona 1/2Heine-Allen-Cardona 1/2
For a review see M. Cardona, Solid State Commun. 133, 3 (2005).
H (x+u)=H (x) + ∂V scf
∂ x u +
12
∂
2V scf
∂ x2 u2 +...
Using Perturbation TheoryPerturbation Theory, we get the correction
to the energy
δ Ei=⟨Ψi(0)∣ ∣Ψi
(0)⟩ + ⟨Ψi
(0)∣ ∣Ψ i
(0)⟩ + ⟨Ψi
(0)∣ ∣Ψi
(1)⟩ +...
First order PT Second order PT
V scf (x+u)=V scf (x) + ∂V scf
∂ x u +
12
∂
2V scf
∂ x2 u2 +....
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A perturbative approach:A perturbative approach:Heine-Allen-Cardona 2/2Heine-Allen-Cardona 2/2
Debye-Waller Fan
δ Ei(β) = [12
⟨∂
2V scf
∂ x2⟩ + ∑ j
(Ei−E j)−1
⟨∂V scf
∂ x∣j ⟩ ⟨ j∣
∂V scf
∂ x⟩] ⟨u2
⟩
Clear dependence on the Temperature
B(w) = Bose function
δ En k (β)=∑q λ n '[
∣gn n' kqλ ∣
En k−En ' k+q
−Λnn ' k
q λ
En k−En ' k
](2B (ωq λ)+1)
Thermal average
Average on theelectronic
wavefunction
FINAL FORMULA
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All the previous theory can be reformulated in term of Green's function including nonadiabatic effects
Beyond the static Beyond the static perturbation theoryperturbation theory
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Electron-phonon coupling from a MBPT perspective
ϵn k En k(T )+iΓn k(T )
Electron scatters with 1 phonon at a time
ElectronPhonon Self Energy
Temperature dependenceSpectral Functions
Enk
Γnk
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Born–Oppenheimer approximation Born–Oppenheimer approximation
a perturbative approacha perturbative approach
Electron phonon coupling at workElectron phonon coupling at work
beyond the beyond the Born–Oppenheimer approximationBorn–Oppenheimer approximation
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Spectroscopy: theoretical point of
viewWhat really theoreticians
calculate!!
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Finite temperature electronic Finite temperature electronic and optical and optical
properties of zb-GaNproperties of zb-GaN
H. Kawai, K. Yamashita, E. Cannuccia, A. MariniPhys. Rev. B. 89, 085202 (2014)
What we can
do now!!!BroadeningBroadening induced
by electron-phonon scattering andtemperature dependence
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The gap of diamond The gap of diamond (1/2)(1/2)
F. Giustino, et al. PRL, 105, 265501 (2010)E. Cannuccia, Phys. Rev. Lett. 107, 255501 (2011)
Logothedis et al. PRB 46, 4483 (1992)
Electronic Gap: 7.715 eV
Renormalization: ~400 meV
Classical ions
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The gap of diamond The gap of diamond (2/2)(2/2)
Exp: Logothetidis et al.PRB 46, 4483 (1992)
Quantum (PI)MD calculations
Ramirez et al. PRB 73, 245202 (2006)
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Isotopic EffectsIsotopic Effects
⟨u2⟩=⟨
h4Mω
{2[e−hω/KT−1]
−1+1}⟩
At high T, independent of M (classical effect)
At low T, zero point vibrations (quantum)
⟨u2⟩∝KT
⟨u2⟩∝M−1/2
The quantistic The quantistic zero-point zero-point
motion effectmotion effect
Parks et al. PRB 49,14244 (1994)
This renormalization should be taken into account when state of the art ab initio calculations of the gap are
comparedwith experimental results.
Eg
MM→∞Eg electronic
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Shrinking of the gapShrinking of the gap
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It's time to revise previous electronic structure
calculations?
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What about dynamical effects?What about dynamical effects?
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Dynamical effects in diamondDynamical effects in diamond
Logothedis et al. PRB 46, 4483 (1992)
E. Cannuccia, Phys. Rev. Lett. 107, 255501 (2011)
Signature of Signature of the dynamical the dynamical
effectseffects
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Breakdown of the QP pictureBreakdown of the QP picture
E. Cannuccia and A. MariniE. Cannuccia and A. Marini
Europ. Phys. J. B. Europ. Phys. J. B. 8585, 320 (2012), 320 (2012)
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What if LDA fails to describe the electron-phonon coupling?
What if the electron-phonon coupling causes degeneracy and crossing of quasi-particle levels?
In the next talks......In the next talks......
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ConclusionsConclusions Perturbative approach to the electronphonon coupling
Finite temperature optical spectra
Band gap renormalization induced by the EPC
Dynamical effects on the electronic properties
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Thank you for your attention
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S. Ponce, G. Antonius, P. Boulanger, E. Cannuccia, et al. Comp. Mat. Science, 83, 341, (2014)
Implementation of large formula: source of infinite
errors but ...
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Carbon contributionSi contrib.
TotalRenorm.
Temp. Dep. of gap: SiC, path integral molecular dynamics
Hernández, Herrero, Ramírez, Cardona, PRB 77 045210 2008
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Polarons in an Hamiltonian representation (I)
k kq
k kq
q
q
Phonon population:
Basis setT = 0 °K
H
Many Body
GF's evaluated from the matrix diagonalization are equivalent to the
MB ones
Two bands model
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Polaronic State:
More polarons than electrons!
H
T = 0 °KBasis Set
0
E
Spectral Function
Polarons in an Hamiltonian representation (II)
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A. Eiguren and C. Ambrosch-Draxl, PRL 101 036402 (2008)
Quasi-particle Band Structure Induced by the Electron-phonon interaction on a surface