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WIR SCHAFFEN WISSEN – HEUTE FÜR MORGEN
Phase mixture and pseudogap behavior in the bismuthate high Tc superconductors
Muntaser Naamneh:: SIS beamline @ Swiss Light Source :: Paul Scherrer Institut
Empa Postdocs-II & PSI-Fellow II-3i Retreat
Empa Dübendorf, 21.09.2018
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Page 2
Acknowledgments
• PLD + ARPES team (PSI): N. Plumb, M. Radovic, J. Jandke , J. Ma, M. Yao, M. Shi, J. Mesot • Materials: D. Gawryluk, T. Shang, M. Medarde, K. Conder, E. Pomjakushina • Theory: Y. Wang, S. Li, S. Johnston (U. Tennessee Knoxville), T. Berlijn (Oak
Ridge Nat’l Lab), M. Müller (PSI)
• Raman: J. Teyssier, A. Stucky, D. van der Marel (U. Geneva)
This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 701647
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Unconventional superconductors
Strongly correlated systems
Page 3 Nature volume438, pages474–478 (24 November 2005)
Manganites
Transition metal dichalcogenides Rare earth nickelates
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Pseudogap term is used in all of this materials to describe a suppression of spectral weight with no obvious symmetry breaking.
Pseudogap
Page 4
What is the origin of the pseudogap?
Nature volume438, pages474–478 (24 November 2005)
Phys. Rev. Lett. 80, 149, 1998
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Ba1-xKxBiO3 phase diagram
Page 5 An overview: A. W. Sleight, Physica C 514, 152 (2015)
• 3D perovskite structure. • Parent compound insulating behavior is linked to lattice distortions in the form of breathing
mode • SC emerges with doping. Tc = 32 - 34 K (x ~ 0.38) from insulating parent compound. • No magnetic order. SC is phonon-mediated (isotope shift in Tc)
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Electronic structure of the Parent Compound Freezed lattice of bipolarons
Page 6 Plumb et al., PRL 117, 037002 (2016)
• The Brillouin zone is folded due to breathing distortions of insulating.
• The BaBiO3 insulator is negative charge transfer insulator, similar to the nickelates.
Bi3+
6s
E
EF
2p
2p E
EF
6s
Foyevtsova, Sawatzky, et al., PRB 91, 121114(R) (2015)
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Fermi surface (x = 0.34)
Page 7
Bin
ding
Ene
rgy
(eV
)
-0.3
-0.22
-0.16
-0.09
EF
Max
Min
E b[eV]
0
-0.05
-0.1
-0.2
-0.25
-0.15
-0.30 0.5 1 0.5 1
k[Å-1] k[Å-1]
E b[eV]
0
-0.05
-0.1
-0.2
-0.25
-0.15
-0.30 0.5 1 0.5 1
k[Å-1] k[Å-1]
At temperatures below Tp, a spectral weight near Ef is reduced
G-M
G
-X
T=17K T=200K
TB: Sahrakorpi et al, PRB 61, 7388 (2000).
k z
kx
Γ
X M
Naamneh et al., arxiv:1808.06135
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Electronic structure of BKBO: pseudogap
Page 8
• Quasiparticle peak is absent. • The spectral weight is suppressed below Tp. • The reduction is isotropic at Ef. • The redistribution of the weight is anisotropic
at deep binding energies.
Bin
ding
Ene
rgy
(eV
)
-0.3
-0.22
-0.16
-0.09
EF
Max
Min
70
60
50
40
30
20
10
-0.4 -0.2 0.0 0.2Binding Energy (eV)
Inte
nsity
(cou
nts
rate
a.u
.)
T=17 KT=50 K
T=290 KT=200 K
α=0.6
Γ-M 100
80
60
40
20
-0.4 -0.2 0.0 0.2Binding Energy (eV)
Inte
nsity
(cou
nts
rate
a.u
.)
Γ-X 14
12
10
8
6
4
100500-50
α=0.6
Binding Energy (meV)
Inte
nsity
T=17 KT=50 K
T=290 KT=200 K
See also -Karlow et al., PRB 48, 6499 (1993) -Chainani et al., PRB 64, 180509 (2001)
2. Precipitation of frozen bipolarons (metal-insulator phase mixture)
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Phase separation- cuts
Page 9
0
-0.1
-0.2
-0.30 0.5 1
k(Å-1)
Bin
ding
Ene
rgy
(eV
)
T=17K
Insulator+Metal
𝐼𝐼𝐿𝐿𝐿𝐿𝐿𝐿𝑇𝑇 (𝐸𝐸𝐹𝐹 , 𝑘𝑘𝐹𝐹)𝐼𝐼𝐻𝐻𝐻𝐻𝐻𝐻𝐻𝑇𝑇 (𝐸𝐸𝐹𝐹 , 𝑘𝑘𝐹𝐹)
−
α
0 0.5 1k(Å-1)
T=200K
Metal
=
Subtracted
0 0.5 1k(Å-1)
-0.4
-0.3
-0.2
-0.1
0 0.5 1k(Å-1)
Bin
ding
Ene
rgy
(eV
)
Max
Min
Insulator
Superconducting BKBO Insulating BKBO
Naamneh et al., arxiv:1808.06135
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Phase separation-Fermi Surface
Page 10
-0.4
-0.32
-0.26
-0.19
-0.1
Bin
ding
Ene
rgy
(eV
)
-0.3
-0.22
-0.16
-0.09
EFГ
XM
ГX
M
Superconducting BKBO Insulating BKBO
T>Tp
T<Tp
T=17K T=200K Subtracted
Single scaling value.
Naamneh et al., arxiv:1808.06135
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Raman scattering
11
• Breathing distortion peak at all temperatures, in contrast with neutrons
• Local distortions embedded/fluctuating in a different global symmetry
• Similar findings in nickelates:
Little happening in structural probes. Why is there an electronic transition to phase separation?
Li et al., Adv. Electron. Mater. 2, 1500261 (2016). Shamblin et al, Nat. Commun. 9, 86 (2018).
BiO6
breathing
Naamneh et al., arxiv:1808.06135
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ARPES view of electronic scattering
12
Subtracted spectra
Insulating bands
MDC
wid
th @
EF (
1/Å)
Onset when scattering at EF corresponds to electron mean free path = 2a.
Formation of insulator impeded by (lack of) electronic coherence.
Naamneh et al., arxiv:1808.06135
At X point (near vHs)
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Doping dependence of Tp
13
Naïve picture: Higher doping lower Tp (further from insulator) … WRONG!
Scattering picture: Higher doping less scattering higher Tp … OBSERVED!
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• Depending on definition, we observe two types of PG: − Appear below Tp and be regarded as true bandgap whose origin and underlying
symmetry had been obscured by phase separation.
− Broad energy suppression approaching Ef persisting to room temperature and characterized by an absence of QP peak.
• Both pseudogaps stem from bi-polarons interactions.
• The phase separation is driven by scattering rather than change in the lattice.
Conclusions
Page 14
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Very dispersive bands with no QPs?
28.09.2018 15
Sous et al., arxiv: 1805.06109
In Su-Schrieffer-Heeger model, (bi)polaron “wants” to hop. Strong coupling doesn’t necessarily imply high mass.
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Unique tools at the SIS beamline
Page 16
Our approach: In situ spectroscopy on thin films
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Electronic structure of BKBO: pseudogap
Page 17
70
60
50
40
30
20
10
-0.4 -0.2 0.0 0.2Binding Energy (eV)
Inte
nsity
(cou
nts
rate
a.u
.)
T=17 KT=50 K
T=290 KT=200 K
α=0.6
Γ-M 100
80
60
40
20
-0.4 -0.2 0.0 0.2Binding Energy (eV)
Inte
nsity
(cou
nts
rate
a.u
.)
Γ-X 14
12
10
8
6
4
100500-50
α=0.6
Binding Energy (meV)
Inte
nsity
T=17 KT=50 K
T=290 KT=200 K
R. S. Dhaka et al, Phys. Rev. B 92, 035127 (2015)
Naamneh et al., arxiv:1808.06135
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Phase separation simulation-Model
Page 18
Minimizing the energy of the system with correspond to the O displacement.
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Phase separation simulation-Results
Page 19
MГX-12
-8
-4
0
4b n = 1
Bind
ing
ener
gy (e
V)
c
MГX
n = 1.4
MГX
Bind
ing
ener
gy (e
V)
-12
-8
-4
0
4
Momentum
n = 1.2
MГX
Mixed
Momentum
f
Intermediate doping behaves as a suppression of metallic and insulator.
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Doped “normal state” transport
28.09.2018 20
Nagata et al., J. Phys. Chem. Solids 60, 1933 (1999).
Our films Single crystals
x = 0.34 x = 0.39
x = 0.48 x = 0.62
Naamneh et al., arxiv:1808.06135
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Same signatures in single crystals
Page 21
k-integrated PES Chainini et al., PRB 64, 180509(R) (2001).
Transport
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TEM: Phase separation in BaPBiO3
Page 22 Giraldo-Gallo, P. el al, Nat. Commun. 6, 8231 (2015).
10nm
structural polymorphs is detected by TEM in superconducting sample of BaPb1-xBixO3. The system is ordered in nano-stripes having different structures, tetragonal and orthorhombic. Maximum Tc occurs when the superconducting coherence length matches the width of the partially disordered stripes.
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Debates surrounding insulating phase
Page 23
Classical picture Bi charge order
6s
E
EF
2p
2p
E
EF
6s
Alternative proposal “Bond disproportionation”
• Rice, Varma, et al in 80s: gap opened by attractive effective on-site interaction (-U) • Not clear a priori whether we can trust single-electron calculations
e.g.: Foyevtsova et al., PRB 91, 121114(R) (2015)
Picture: Franchini et al., PRB 81, 085213 (2010)
VS.
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The evolution of constant energy map with doping up to superconductivity.
Doped BKBO
Page 24
Percolation picture from insulator to superconducting
X=40%, E=Ef x=25% , E=-0.2eV x=10% , E=-0.2eV x=2% , E=-0.2eV
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Polarization dependence
Page 25
Plumb et al., PRL 117, 037002 (2016)
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Angle-resolved photoemission spectroscopy
Page 26 Review: Damascelli,Physica Scripta T109, 61-74 (2004).
ARPES can map electronic structure in 4
dimensions
(E, kx, ky, kz)
Strontium ruthenate. Baumberger Group, U. Geneva
STO. Nature 469, 189 (2011).
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Half filled bi-polarons
Page 27
Bi3+
2p
E
EF
6s
-U ???
• Polarons cannot move independently when there lattice distortions overlap.
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• LDA methods successfully compute most aspects of the band structure of BaBiO3.
• The electron correlations are weak.
Weak electronic correlations
Page 28
zero-, single-, bi-polaron state