phase mixture and pseudogap behavior in the bismuthate ... · phase mixture and pseudogap behavior...

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

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

Unconventional superconductors

Strongly correlated systems

Nature volume438, pages474–478 (24 November 2005)

Manganites

Transition metal dichalcogenides Rare earth nickelates

Pseudogap term is used in all of this materials to describe a suppression of spectral weight with no obvious symmetry breaking.

Pseudogap

What is the origin of the pseudogap?

Nature volume438, pages474–478 (24 November 2005)

Phys. Rev. Lett. 80, 149, 1998

Ba1-xKxBiO3 phase diagram

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)

Electronic structure of the Parent Compound Freezed lattice of bipolarons

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)

Fermi surface (x = 0.34)

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

Electronic structure of BKBO: pseudogap

• 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


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)

Phase separation- cuts

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


Phase separation-Fermi Surface

-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.


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


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.


At X point (near vHs)

Doping dependence of Tp

13

Naïve picture: Higher doping lower Tp (further from insulator) … WRONG!

Scattering picture: Higher doping less scattering higher Tp … OBSERVED!

• 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

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.

Unique tools at the SIS beamline

Our approach: In situ spectroscopy on thin films

Electronic structure of BKBO: pseudogap

70

60

50

40

30

20

10


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


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)


https://arxiv.org/find/cond-mat/1/au:+Dhaka_R/0/1/0/all/0/1

Phase separation simulation-Model

Minimizing the energy of the system with correspond to the O displacement.

Phase separation simulation-Results

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.

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


Same signatures in single crystals

k-integrated PES Chainini et al., PRB 64, 180509(R) (2001).

Transport

TEM: Phase separation in BaPBiO3

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.

Debates surrounding insulating phase

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.

The evolution of constant energy map with doping up to superconductivity.

Doped BKBO

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

Polarization dependence

Plumb et al., PRL 117, 037002 (2016)

Angle-resolved photoemission spectroscopy

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).

Half filled bi-polarons

Bi3+

2p

E

EF

6s

-U ???

• Polarons cannot move independently when there lattice distortions overlap.

• LDA methods successfully compute most aspects of the band structure of BaBiO3.

• The electron correlations are weak.

Weak electronic correlations

zero-, single-, bi-polaron state

phase mixture and pseudogap behavior in the bismuthate ... · phase mixture and pseudogap behavior...

Documents