1. Superconductivity in Ba1-XKXBiO3(BKBO)
I’m Shouta Maki. I am a member of Kitaoka Lab. Today I talk about SC in BaKBiO3 called BKBO.
Kitaoka Lab.
M1 Maki Shouta
H. Matsuura and K. Miyake, J. Phys. Soc. Jpn. 81 (2012)
C. Varma PRL (1988)
Physica B 296 (2001) 112}119 W.E. Pickett
JETP LETTERS VOLUME 70, NUMBER 5 K. N. Mikhalev, S. V. Verkhovski et.al
K.Kumagai.et,al Physica C 274 (l 997)
B. A. Baumert et.al. Barium Potassium Bismuth Oxide: A Review

2. Introduction Discussion Contents My work Summary
-Ba1-XKXBiO3(BKBO)&BaBiO3(BBO)
-Valence Skipper(VS)
-VS relate to Superconductivity(SC)
My work
Summary
This contents of my presentation are shown here. In Introduction, I talk about the history and properties of oxide SC. In discussion, First I talk about BKBO and BBO structure and K doping effect on BKBO. Second what is VS? and relationship of VS and SC. Next my work and summary. 1
contents

3. Introduction spin Spin + orbital phonon Spin/valence 1 1975 Tcmax~12K
BaPbXBi1-XO3
1988
TCmax~30K
Spin +
orbital
Ba1-XKXBiO3
First, I introduce the history of searching high-Tc SC. In 1975, BaPbBiO3 was discovered. The Tc was 12K and this was the first SC in oxides. After that, the related oxide BaKBiO3 was discovered in The Tc was about 30K which was twice higher than BPBO. At that time, people believe that these SC can be explained within the BCS thory. But, now, we know that there are many SC mechanisms. For example, the SC of cuprate must be explained by spin mechanism, that of heavy electron system is by spin or valence, iron based system is by spin and orbital and so on. So we try to reconsider the mechanism of BKBO again.
1988年には銅酸化物と同じペロブスカイト構造を取る酸化物のBa1-xKxBiO3[9]が30 Kで超伝導を示す物質として発見されました。現在でも銅酸化物を除
いた酸化物超伝導体の中では、最高のTcを持っています。この物質では、電荷密度波(CDW = Charge Density Wave)が超伝導と密接に関連してるのではないかといわれています。
phonon
Spin/valence 1
Introduction

4. Phase diagram in Ba1-XKXBiO3(BKBO)
K concentration X
TC~30K at X=0.37
On set
Off set
No magnetic phase
Low carrier=5×1021/cm3
Next. In this slide, I talk about the properties of BKBO. The BKBO has the perovskite structure like this. Please look at right figure. When K concentration is smaller than 30%, the BKBO is not SC. However when K concentration is over 37%, the BKBO become SC suddenly. The BKBO doesn’t have magnetic phase and has high Tc irrespective of low carrier density. Today the Tc is the highest in oxide without cuprate. So this BKBO SC mechanism attracts much attention again, recently
Highest TC in oxide
(without cuprate) 2
introduction-BKBO

5. Previous study of BKBO system
Please look at the figure. The Tc was plotted as a function of 6s electron of Bi or Pb. The number of 6s electron is changed by replacing the Ba with K. And the relationship of the number of 6s electron and Tc among the related oxides is summarized in this figure. This means that Tc becomes high when number of 6s electron approaches one
Bi(Pb) 6s electrons 3
introduction-BKBO

6. Parent material BaBiO3(BBO)
Band calculation
H. Matsuura and K. Miyake, J. Phys. Soc. Jpn. 81 (2012) Ba
Bi4+ 2+ 2-
Tilting
and
Breathing
Insulator
Band gap 2eV
Ionic radii (Å)
Ba2+
　1.61
Bi3+
　1.03
Bi4+(6s)1
Bi5+
　0.76
metallic
(6s)2
charge density wave(CDW) state
If this Perovskite structure is Cubic , the behavior is metallic when we calculate the band gap. R q
(6s)0
Bi3+
Bi5+
-2e 1
discussion-BKBO 0e

7. Crystal structure and distortion
I2/m
Ibmm
Pm3m
lattice systems 
Space group
Lattice image
 rhombohedral
 monoclinic
orthorhombic
 cubic R3
T(K)
solubility limit
I2/m
Ibmm
Pm3m
Ba1-XKXBiO3(BKBO) SC 2
discussion-BKBO
B. A. Baumert et.al. Barium Potassium Bismuth Oxide: A Review

8. K doping effect in Ba1-XKXBiO3(BKBO)R3
I2/m
Ibmm
Pm3m
K dope ↓
Hole dope
Ionic radii (Å) K+
　1.64
Ba2+
　1.61
T(K)
solubility limit
Commensurate CDW
　→　Incommensurate CDW
Tcmax~30K
on set
off set
Temperature↑
and
K concentration↑
X~0.37
suppression of structural distortion
K concentration X 3
discussion-BKBO

9. Properties of Ba1-XKXBiO3(BKBO)
I2/m
Ibmm
Pm3m
solubility limit
T(K) SC ×
0.1
0.37
0.5
Insulator
Semiconductor
Metallic
Monoclinic
Orthorhombic
Cubic
Tilting
&
breathing
No?
Distortion
Structure
Band gap 4
discussion-BKBO

10. Superconductivity gap in BKBO＋
2Δ/kTC =3.5±0.5
Full gap
Week-coupling SC 5
discussion-BKBO

11. × BCS superconductivity? TC∝ ∝(1/M)α high TC
Physica B 296 (2001) 112}119 W.E. Pickett α
TC∝ ∝(1/M)α
M:isotope mass
BCS ×
Low carrier=5×1021/cm3
high TC
Electron-phonon interaction
constant λ=0.2
We can not explain the high TC in this material with BCS
The valence skip is important in the study of "Charge Kondo effect" as well as valence - fluctuation induced SC
New theory
Valence Skipper relate to SC mechanism? 6
discussion-BKBO

12. What is Valence Skipper?
Missing valence state (ns)1
For example
Bi3+
Bi5+
[Xe](4f)14(5d)10(6s)2(6p)0
[Xe](4f)14(5d)10(6s)0(6p)0
Bi4+
[Xe](4f)14(5d)10(6s)1(6p)0
induce negative U
6s0
6s1
6s2
for example, Tl and In form compounds with the valence states +1 and +3, Bi and Sb form with +3 and +5 states, and Pb and Sn with +2 and +4 valence state.
H. Matsuura and K. Miyake, J. Phys. Soc. Jpn. 81 (2012)
condition 7
discussion-VS

13. Theory of SC by VS CDW SC t≪Δ eliminate the flexibility of oxygen x
C. Varma PRL(1988)
U:intra-atomic repulsion parameter(Bi-Bi)
t:hopping(Bi-O)
V:intra-atomic repulsion parameter(Bi-O)
Δ:level
CDW SC x
t≪Δ
eliminate the flexibility of oxygen
attraction-repulsion AF SC x
ccccccccc
Bi3+
Bi5+ 9
discussion-BKBO

14. ? 39K-NMR in Ba1-XKXBiO3(BKBO) × R3 Ibmm Pm3m half-height 3kHz.
I2/m
Ibmm
Pm3m
solubility limit
half-height 3kHz.
39K NMR
X=0.5
X=0.4
Spectrum dose not change
by T and K concentration
X=0.3
Here T1e-1 is the contribution due to the interaction of nuclear spins with the conduction
electrons ~Korringa contribution! and T1Q-1 is the contribution due to the interaction of the
quadrupole moment of potassium with the electric field gradient ~EFG!, modulated by
motion in the lattice.
The smallness of this value and the fact that the
relaxation rates for all experimental samples at T520 K are essentially the same, suggests
that the Korringa contribution is the same for all the samples investigated, and it can
be subtracted from the experimental data. ×
K’s s electron
Conduction band ? 9
discussion-BKBO
JETP LETTERS VOLUME 70, NUMBER 5 K. N. Mikhalev, S. V. Verkhovski et.al

15. 39K-NMR in Ba1-XKXBiO3(BKBO)
JETP LETTERS VOLUME 70, NUMBER 5 K. N. Mikhalev, S. V. Verkhovski et.al
T1-1(s-1)
T(K)
X=0.5
X=0.4
X=0.3
T1Q-1(s-1)
1000/T(1/K)
X=0.5
X=0.4
X=0.3
x small → peak large
T1-1(s-1)
T(K)
Normal
metallic
K.Kumagai.et,al Physica C 274 (l 997)
BaPbXBi1-XO3
137Ba/135Ba-NMR
T1Q-1
(137eQ/135eQ)=2.4
Valence fluctuation large
T1e-1
(137γ/135γ)=1.2
eQ : Quadrupole moment
γ : gyromagnetic ratio 10
discussion-BKBO
(137T1-1/135T1-1)=2.1 at T＞80K

16. Evidence of valence fluctuationR3
I2/m
Ibmm
Pm3m
T1Q-1(s-1)
1000/T(1/K)
X=0.5
X=0.4
X=0.3
T(K)
solubility limit
Valence fluctuation is
largest nearly Tcmax
on set
off set
CDW
X~0.37 11
discussion-BKBO
K concentration X

17. Evidence of valence fluctuation
T1Q-1(s-1)
1000/T(1/K)
X=0.5
X=0.4
X=0.3
X~0.37
K concentration X
CDW
Likely behavior
Heavy electron system
Cuprate 12
discussion-BKBO

18. Bi(Pb) 6s electrons relate to TC?
on set
off set
6s0.4
6s1
K concentration X
There is a tendency for TC to become high,
so that 6s electron is close to 1.
Bi(Pb) 6s electrons
TCmax~50K is limit ? 13
discussion-BKBO
H. Matsuura and K. Miyake, J. Phys. Soc. Jpn. 81 (2012)

19. My work Pb1-xTlxTe Low carrier ~ 1018~19/cm3 VS 1 TC~0.3K at X=0.3% 6s
X(at.%)
TC~0.3K at X=0.3%
Pb1-xTlxTe
0.646nm
image
NaCl structure
(space group Fm3m) VS 6s
Tl+
・・・
Tl3+
Tl+
Tl3+ 0e
-2e 1
My work

20. Summary
Ba1-XKXBiO3(BKBO) reaches highest TC at X=0.37 irrespective of low carrier density.
Some results are consistent with BCS theory.
In Tcmax, valence fluctuation becomes maximum.
Valence Skipper
Bi Bi5+
Tl Tl3+ ⇔
Finally, let me summarize my talk. BKBO has high TC irrespective of low carrier density. Some results are consistent with BCS theory however any results are not. In sample with highest Tc, valence fluctuation becomes maximum. So SC may be explained by VS mechanism which cause the high Tc SC. Thus VS is so interesting in researching high Tc SC.
High TCSC ? 1
Summary

21. Thank you for your listening
END

22. appendix

23. Theory of SC by VS CDW SC ~ 1 – t4/z2|U|2V2
C. Varma PRL(1988)
U:intra-atomic repulsion parameter(Bi-Bi)
t:hopping(Bi-O)
V:intra-atomic repulsion parameter(Bi-O)
Δ:level
attraction-repulsion
CDW SC
~ 1 – t4/z2|U|2V2 x
t≪Δ
eliminate the flexibility of oxygen 9
discussion-BKBO x

24. Phase diagram in Ba1-XKXBiO3(BKBO)
K concentration X
TC~30K at X=0.37
On set
Off set
No magnetic phase
Low carrier
Bi(Pb) 6s electrons
Highest TC in oxide
(without cuprate) 2
intriduction-BKBO

25. ? × × BCS superconductivity? TC∝ ∝(1/M)α 6
Physica B 296 (2001) 112}119 W.E. Pickett α
TC∝ ∝(1/M)α
M:isotope mass ×
BCS theory
Low-carrier
high TC ?
We can not explain the high TC in this material with BCS
The valence skip is important in the study of "Charge Kondo effect" as well as valence - fluctuation induced SC ×
Electron-phonon interaction
constant λ=0.2
K concentration X 6
discussion-BKBO
New theory
Valence Skipper relate to SC mechanism?

26. CDW SC Properties of Ba1-XKXBiO3(BKBO) U,V ⇒ larger ~ 1 – t4/z2|U|2V2
I2/m
Ibmm
Pm3m
CDW SC
U,V ⇒ larger
T(K)
High TC???
~ 1 – t4/z2|U|2V2 x ×
0.1
0.37
0.5
Insulator
Semiconductor
Metallic
Monoclinic
Orthorhombic
Cubic
Tilting
&
breathing
No?
Distortion
Structure
Band gap 13
discussion-BKBO

27. Theory of SC by VS CDW SC t≪Δ eliminate the flexibility of oxygen x
C. Varma PRL(1988)
U:intra-atomic repulsion parameter(Bi-Bi)
t:hopping(Bi-O)
V:intra-atomic repulsion parameter(Bi-O)
Δ:level
CDW SC x
Bi3+
Bi5+
t≪Δ
eliminate the flexibility of oxygen
attraction-repulsion AF SC x
Heavy electron system
ccccccccc 9
discussion-BKBO

28. charge density wave(CDW) state
Bi+3
Bi+5
charge density wave(CDW) state R q
Bi3+
Bi5+

29. CDW SC ~ 1 – t4/z2|U|2V2 AF SC AF SC x Heavy electron system x AF + SC
(K)
Hole or electron dope (high TC SC)
Pressure (heavy electron system)
CDW SC
~ 1 – t4/z2|U|2V2 x AF + SC AF SC x
Heavy electron system

30. Phase Diagram of HF system
TK ∝ W exp(-1/J cf D(εF))
TRKKY ∝ D(εF) Jcf2
AFM : antiferromagnetism
HF　 : heavy fermion state
QCP : quantum critical point
<
( )
γ＝ρ(f)J 30

32. SC ,which has VS in the origin ,appearing condition
Summary
1.BKBO
SC ,which has VS in the origin ,appearing condition
1.nearing CDW (due to VS)
2.condition which chemical potential is pinned when VS is doped
How to rise the TC
1.control CDW (structure)
2.negative U become large 1
Summary
2.PbTlTe

33. 同位体効果
TC∝(1/M)αj

34. Properties of Ba1-XKXBiO3(BKBO)
K dope ↓
Hall dope
Ionic radii (Å) K+
　1.64
Ba2+
　1.61
Incommensurate CDW
Tcmax=30K
Temperature
and
K substitution
on set
off set
Tc≒30K　and　has metallic behavior　at X≧0.37
suppression of structural distortion
X~0.37
K concentration X 2
discussion-BKBO

35. まとめ ・バレンススキッピング起源の超伝導 が出てきそうな所 １．バレンススキッパー起源のCDW付近
２．バレンススキッパーをドープしていき、
　　化学ポテンシャルがピン止めされるところ
３．Ag酸化物の可能性
・転移温度を上げる方法
1. 価数を制御する（→結晶構造の制御）
2. 波動関数の広がりが大きいと
ネガティブ-Uが大きくなる。
周期表で下の元素を使う。

36. What is charge density wave(CDW)?
Ionic radii (Å) K+
　1.64
Ba2+
　1.61
Bi3+
　1.03
Bi5+
　0.76 5
Introduction-VS

37. すこし理論の話
C. Varma PRL(1988)
引力-斥力変換の対応
酸素の自由度の消去
引力-斥力変換
二次摂動

38. "Tilting" and "Breathing" distortion
Breathing refers to distotion due to the BiO6 octahedra expanding and shrinking alternatly in the perovskite structure.
tilting of BiO6 octahedra brings about the lowering of the
symmetry of the structure from cubic to monoclinic or rhombohedral 5
Introduction-VS

39. 同位体効果

40. No-tilt sample (thin film)

41. 5 × 0.1 0.37 0.5 Insulator Semiconductor Metallic Monoclinic
0.37
0.5
Insulator
Semiconductor
Metallic
Monoclinic
Orthorhombic
Cubic
Tilting
&
breathing
No?
Distortion
Structure
Band gap 5
Summary

42. X
Charge density

43. R q
Bi3+
Bi5+
ρ(μΩ)
TC~11K
BaPb0.8Bi0.2O3

44. BaBiO3(BBO)&Ba1-XKXBiO3(BKBO)
These material has Perovskite structure with “tilting” and “breathing”.
In addition to band structure calcuration , BBO is metallic.However BBO is insulater　with band gap 2eV . 5
Introduction-BKBO