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Superconductivity in Ba 1-X K X BiO 3 (BKBO) Kitaoka Lab. M1 Maki Shouta H. Matsuura and K. Miyake, J. Phys. Soc. Jpn. 81 (2012) 11370581 C. Varma PRL.

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Presentation on theme: "Superconductivity in Ba 1-X K X BiO 3 (BKBO) Kitaoka Lab. M1 Maki Shouta H. Matsuura and K. Miyake, J. Phys. Soc. Jpn. 81 (2012) 11370581 C. Varma PRL."— Presentation transcript:

1 Superconductivity in Ba 1-X K X BiO 3 (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 Contents ▪Introduction ▪Discussion -Ba 1-X K X BiO 3 (BKBO)&BaBiO 3 (BBO) -Valence Skipper(VS) -VS relate to Superconductivity(SC) ▪My work ▪Summary 1 contents

3 Introduction 1 T C max~30K Ba 1-X K X BiO spin Spin + orbital phonon Spin/valence BaPb X Bi 1-X O 3 T c max~12K 1975

4 Phase diagram in Ba 1-X K X BiO 3 (BKBO)2 introduction-BKBO K concentration X Highest T C in oxide (without cuprate) Low carrier=5×10 21 /cm 3 T C ~30K at X=0.37 On set Off set No magnetic phase

5 Previous study of BKBO system3 introduction-BKBO BKBO Bi(Pb) 6s electrons

6 Parent material BaBiO 3 (BBO)1 discussion-BKBO Ionic radii ( Å ) Ba Bi Bi 4+ (6s) 1 Bi Ba Bi 4+ metallic Insulator Band gap 2eV Tilting and Breathing charge density wave(CDW) state (6s) 2 (6s) 0 -2e 0e Bi 3+ Bi 5+ Bi 3+ Bi 5+ R q H. Matsuura and K. Miyake, J. Phys. Soc. Jpn. 81 (2012) Band calculation

7 R3 I2/m Ibmm Pm3m lattice systems Space groupLattice image rhombohedra lrhombohedra l monoclinic orthorhombic cubic I2/m Ibmm Pm3m 2 discussion-BKBO Crystal structure and distortion Ba 1-X K X BiO 3 (BKBO) T(K) B. A. Baumert et.al. Barium Potassium Bismuth Oxide: A Review solubility limit R3 SC

8 R3 I2/m Ibmm Pm3m K doping effect in Ba 1-X K X BiO 3 (BKBO)3 discussion-BKBO Temperature↑ and K concentration↑ suppression of structural distortion Commensurate CDW → Incommensurate CDW Ionic radii ( Å ) K+K Ba K dope ↓ Hole dope X~0.37 K concentration X on set off set T c max~30K T(K) solubility limit

9 Properties of Ba 1-X K X BiO 3 (BKBO)4 discussion-BKBO R3 I2/m Ibmm Pm3m solubility limit × Insul ator Semiconductor Metallic MonoclinicOrthorhombic Cubic Tilting & breathing Tilting No? Distortion Structure Band gap T(K) SC

10 Superconductivity gap in BKBO5 discussion-BKBO + 2Δ/kT C =3.5±0.5 Full gap Week-coupling SC

11 BCS superconductivity? Electron-phonon interaction constant λ=0.2 Low carrier=5×10 21 /cm 3 high T C Valence Skipper relate to SC mechanism? New theory 6 discussion-BKBO Physica B 296 (2001) 112}119 W.E. Pickett α M:isotope mass T C ∝ ∝ (1/M) α BCS ×

12 6s 0 6s 1 6s 2 What is Valence Skipper? ▪induce negative U Missing valence state (ns) 1 Bi 3+ Bi 5+ [Xe](4f) 14 (5d) 10 (6s) 2 (6p) 0 [Xe](4f) 14 (5d) 10 (6s) 0 (6p) 0 For example condition 7 discussion-VS Bi 4+ [Xe](4f) 14 (5d) 10 (6s) 1 (6p) 0 H. Matsuura and K. Miyake, J. Phys. Soc. Jpn. 81 (2012)

13 AF SC x CDW SC x C. Varma PRL(1988) Theory of SC by VS U:intra-atomic repulsion parameter(Bi-Bi) t:hopping(Bi-O) V:intra-atomic repulsion parameter(Bi-O) Δ:level t≪Δt≪Δ eliminate the flexibility of oxygen ccccccccc attraction-repulsion 9 discussion-BKBO Bi 3+ Bi 5+

14 39 K-NMR in Ba 1-X K X BiO 3 (BKBO)9 discussion-BKBO half-height 3kHz. 39 K NMR Spectrum dose not change by T and K concentration K’s s electronConduction band × X=0.5 X=0.4 X=0.3 JETP LETTERS VOLUME 70, NUMBER 5 K. N. Mikhalev, S. V. Verkhovski et.al R3 I2/m Ibmm Pm3m solubility limit ?

15 T 1Q -1 (s -1 ) 1000/T(1/K) X=0.5 X=0.4 X= discussion-BKBO 137 Ba/ 135 Ba-NMR ( 137 γ/ 135 γ)=1.2 ( 137 eQ/ 135 eQ)=2.4 T 1e -1 T 1Q -1 ( 137 T 1 -1 / 135 T 1 -1 )=2.1 at T > 80K x small → peak large T 1 -1 (s -1 ) T(K) X=0.5 X=0.4 X=0.3 T 1 -1 (s -1 ) T(K) Normal metallic K.Kumagai.et,al Physica C 274 (l 997) BaPb X Bi 1-X O 3 eQ : Quadrupole moment γ : gyromagnetic ratio Valence fluctuation large JETP LETTERS VOLUME 70, NUMBER 5 K. N. Mikhalev, S. V. Verkhovski et.al 39 K-NMR in Ba 1-X K X BiO 3 (BKBO)

16 R3 I2/m Ibmm Pm3m Evidence of valence fluctuation11 discussion-BKBO X~0.37 K concentration X on set off set T(K) solubility limit Valence fluctuation is largest nearly T c max T 1Q -1 (s -1 ) 1000/T(1/K) X=0.5 X=0.4 X=0.3 CDW

17 X~0.37 K concentration X CDW T 1Q -1 (s -1 ) 1000/T(1/K) X=0.5 X=0.4 X=0.3 Evidence of valence fluctuation12 discussion-BKBO Heavy electron system Cuprate Likely behavior

18 6s 0.4 6s 1 13 discussion-BKBO on set off set K concentration X Bi(Pb) 6s electrons T C max~50K is limit ? Bi(Pb) 6s electrons relate to T C ? H. Matsuura and K. Miyake, J. Phys. Soc. Jpn. 81 (2012)

19 0.646nm image NaCl structure (space group Fm3m) Pb 1-x Tl x Te My work 1 6s Tl + ・・・ Tl 3+ ・・・ Tl + Tl 3+ 0e0e -2 e VS T c (K) X(at.%) T C ~0.3K at X=0.3% Low carrier ~ 10 18~19 /cm 3

20 Summary 1 ▪Ba 1-X K X BiO3(BKBO) reaches highest T C at X=0.37 irrespective of low carrier density. ▪Some results are consistent with BCS theory. ▪In T c max, valence fluctuation becomes maximum. Valence Skipper Bi 3+ Bi 5+ Tl 1+ Tl 3+ ⇔ ⇔ High T C SC ?

21 Thank you for your listening END

22 appendix

23 CDW SC ~ 1 – t 4 /z 2 |U| 2 V 2 x C. Varma PRL(1988) Theory of SC by VS U:intra-atomic repulsion parameter(Bi-Bi) t:hopping(Bi-O) V:intra-atomic repulsion parameter(Bi-O) Δ:level t≪Δt≪Δ eliminate the flexibility of oxygen attraction-repulsion x 9 discussion-BKBO

24 Phase diagram in Ba 1-X K X BiO 3 (BKBO)2 intriduction-BKBO K concentration X Highest T C in oxide (without cuprate) Low carrier T C ~30K at X=0.37 On set Off set Bi(Pb) 6s electrons No magnetic phase

25 BCS superconductivity? BCS theory Electron-phonon interaction constant λ=0.2 ? Low-carrierhigh T C × × Valence Skipper relate to SC mechanism? New theory 6 discussion-BKBO K concentration X Physica B 296 (2001) 112}119 W.E. Pickett α M:isotope mass T C ∝ ∝ (1/M) α

26 × Insul ator Semiconductor Metallic MonoclinicOrthorhombic Cubic Tilting & breathing Tilting No? Distortion Structure Band gap CDW SC Properties of Ba 1-X K X BiO 3 (BKBO) ~ 1 – t 4 /z 2 |U| 2 V 2 R3 I2/m Ibmm Pm3m T(K) 13 discussion-BKBO High T C ??? U,V ⇒ larger x

27 AF SC x Heavy electron system CDW SC x C. Varma PRL(1988) Theory of SC by VS U:intra-atomic repulsion parameter(Bi-Bi) t:hopping(Bi-O) V:intra-atomic repulsion parameter(Bi-O) Δ:level t≪Δt≪Δ eliminate the flexibility of oxygen ccccccccc attraction-repulsion 9 discussion-BKBO Bi 3+ Bi 5+

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

29 AF SC AF + SC T (K) Hole or electron dope (high T C SC) Pressure (heavy electron system) CDW SC ~ 1 – t 4 /z 2 |U| 2 V 2 x AF + SC AF SC x Heavy electron system

30 T K ∝ W exp(-1/J cf D(ε F )) T RKKY ∝ D(ε F ) J cf 2 Phase Diagram of HF system AFM : antiferromagnetism HF : heavy fermion state QCP : quantum critical point < ( ) γ = ρ(f)J

31

32 Summary1 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 T C 1.control CDW (structure) 2.negative U become large 1.BKBO 2.PbTlTe

33 同位体効果 T C ∝ (1/M) αj

34 Properties of Ba 1-X K X BiO 3 (BKBO) X~ discussion-BKBO Temperature and K substitution suppression of structural distortion K concentration X on set off set Incommensurate CDW Ionic radii ( Å ) K+K Ba K dope ↓ Hall dope T c max=30K

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 ・転移温度を上げる方法 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。 3. Ag 酸化物の可能性 1. 価数を制御する( → 結晶構造の制御)

36 What is charge density wave (CDW)? 5 Introduction-VS Ionic radii ( Å ) K+K Ba Bi Bi

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

38 "Tilting" and "Breathing" distortion ▪ "Breathing" ▪"Tilting" 5 Introduction-VS

39 同位体効果

40 No-tilt sample (thin film)

41 × Insul ator Semiconductor Metallic Monoclini c Orthorhombic Cubic Tilting & breathing Tilting No? Distortion Structure Band gap 5 Summary

42 X Charge density

43 Bi 3+ Bi 5+ Bi 3+ Bi 5+ R q BaPb 0.8 Bi 0.2 O 3 T C ~11K ρ(μΩ)

44 BaBiO 3 (BBO) & Ba 1-X K X BiO 3 (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


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