Superconductivity in Ba1-XKXBiO3(BKBO) Kitaoka Lab. M1 Maki Shouta H. Matsuura and K. Miyake, J. Phys. Soc. Jpn. 81 (2012) 113705 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) 209-220 B. A. Baumert et.al. Barium Potassium Bismuth Oxide: A Review Contents ▪Introduction ▪Discussion -Ba1-XKXBiO3(BKBO)&BaBiO3(BBO) -Valence Skipper(VS) -VS relate to Superconductivity(SC) ▪My work ▪Summary 1 contents Introduction 1975 Tcmax~12K spin BaPbXBi1-XO3 1988 TCmax~30K Spin + orbital Ba1-XKXBiO3 phonon 1 Spin/valence Introduction Phase diagram in Ba1-XKXBiO3(BKBO) 40 Ba Bi3+ Bi5+ O Tc (K) 30 (a) TC~30K at X=0.37 Ba1-xKxBiO3 電気抵抗率より決定 20 オンセット On set オフセット Off set 10 No magnetic phase Low carrier=5×1021/cm3 0 0 0.2 0.4 0.6 K濃度 K concentration X x Highest TC in oxide (without cuprate) 2 introduction-BKBO Previous study of BKBO system BaPbO3 KBiO3 BaBiO3 50 Tc (K) 40 30 (Ba,Rb)BiO3 20 10 0 1 BKBO (Ba,K)BiO3 (Ba,K)(Pb,Bi)O3 Ba(Pb,Bi)O3 (Sr,Rb)BiO3 (Sr,K)BiO3 (K,Bi)BiO3 (K,La)BiO3 Ba(Pb,Sb)O3 0.8 0.6 0.4 0.2 0 Bi(Pb) 6s軌道の電子数 Bi(Pb) 6s electrons 3 introduction-BKBO Parent material BaBiO3(BBO) Band calculation H. Matsuura and K. Miyake, J. Phys. Soc. Jpn. 81 (2012) 113705 Ba 2+ Ba Bi3+ Bi4+ 2- Tilting and Breathing Bi5+ O Insulator metallic Band gap 2eV charge density wave(CDW) state q Bi5+ -2e Bi3+ 0e Bi5+ Bi3+ Bi5+ Bi3+ Bi5+ Ba2+ Bi3+ (6s)2 Bi4+(6s)1 Bi5+ (6s)0 Ionic radii (Å) 1.61 1.03 0.76 Bi3+ R 1 discussion-BKBO Crystal structure and distortion lattice systems T(K) R3 I2/m Ibmm solubility limit Pm3m Space group rhombohedra l R3 monoclinic I2/m orthorhombic Ibmm cubic Pm3m Lattice image Ba1-XKXBiO3(BKBO) SC B. A. Baumert et.al. Barium Potassium Bismuth Oxide: A Review 2 discussion-BKBO K doping effect in Ba1-XKXBiO3(BKBO) K dope ↓ Hole dope Pm3m T(K) solubility limit R3 I2/m 40 Tc (K) 30 Ibmm K+ Ba2+ Ionic radii (Å) 1.64 1.61 Commensurate CDW → Incommensurate CDW Ba1-xKxBiO3 (a) Tcmax~30K 電気抵抗率より決定 20 オンセット on set オフセット off set Temperature↑ and K concentration↑ 10 X~0.37 0 0 0.2 0.4 K濃度 x K concentration X 0.6 suppression of structural distortion 3 discussion-BKBO Properties of Ba1-XKXBiO3(BKBO) solubility limit Pm3m T(K) R3 Ibmm I2/m SC Tilting & breathing Distortion Band gap Insul ator Structure Monoclinic 0 No? Tilting Semiconductor Metallic Orthorhombic 0.1 Cubic 0.37 0.5 × 4 discussion-BKBO Superconductivity gap in BKBO + 2Δ/kTC =3.5±0.5 Full gap Week-coupling SC 5 discussion-BKBO BCS superconductivity? α TC∝ ∝(1/M)α M:isotope mass Physica B 296 (2001) 112}119 W.E. Pickett BCS Low carrier=5×1021/cm3 × high TC Electron-phonon interaction constant λ=0.2 New theory Valence Skipper relate to SC mechanism? 6 discussion-BKBO What is Valence Skipper? • Missing valence state (ns)1 For example Bi3+ Bi4+ Bi5+ [Xe](4f)14(5d)10(6s)2(6p)0 [Xe](4f)14(5d)10(6s)1(6p)0 [Xe](4f)14(5d)10(6s)0(6p)0 ▪ induce negative U 6s0 6s1 6s2 H. Matsuura and K. Miyake, J. Phys. Soc. Jpn. 81 (2012) 113705 condition 7 discussion-VS Theory of SC by VS C. Varma PRL(1988) U:intra-atomic repulsion parameter(Bi-Bi) t:hopping(Bi-O) V:intra-atomic repulsion parameter(Bi-O) Δ:level t≪Δ eliminate the flexibility of oxygen CDW SC x attraction-repulsion ccccccccc Bi3+ AF SC Bi5+ 9 xdiscussion-BKBO Ba1-XKXBiO3(BKBO) Pm3m R3 39K NMR half-height 3kHz. I2/m Ibmm solubility limit 39K-NMR in X=0.5 X=0.4 X=0.3 Spectrum dose not change by T and K concentration K’s s electron × ? Conduction band 9 JETP LETTERS VOLUME 70, NUMBER 5 K. N. Mikhalev, S. V. Verkhovski et.al discussion-BKBO 39K-NMR in Ba1-XKXBiO3(BKBO) JETP LETTERS VOLUME 70, NUMBER 5 K. N. Mikhalev, S. V. Verkhovski et.al X=0.3 T1Q-1(s-1) T1-1(s-1) X=0.3 X=0.4 X=0.5 X=0.5 T1-1(s-1) T(K) Normal metallic X=0.4 1000/T(1/K) x small → peak large BaPbXBi1-XO3 137Ba/135Ba-NMR T1Q-1 T(K) T1e -1 (137eQ/135eQ)=2.4 (137γ/135γ)=1.2 eQ : Quadrupole moment γ : gyromagnetic ratio Valence fluctuation large 10 (137T1-1/135T1-1)=2.1 at T>80K K.Kumagai.et,al Physica C 274 (l 997) 209-220 discussion-BKBO Evidence of valence fluctuation X=0.3 T1Q-1(s-1) Pm3m T(K) solubility limit R3 I2/m Ibmm X=0.4 X=0.5 40 Ba1-xKxBiO3 (a) 1000/T(1/K) Tc (K) 30 電気抵抗率より決定 20 Valence fluctuation is largest nearly Tcmax オンセット on set CDW オフセット off set 10 X~0.37 0 0 0.2 0.4 K濃度 x K concentration X 0.6 11 discussion-BKBO Evidence of valence fluctuation T1Q-1(s-1) X=0.3 X=0.4 X=0.5 1000/T(1/K) 40 Likely behavior Ba1-xKxBiO3 (a) Tc (K) 30 Heavy electron system Cuprate 電気抵抗率より決定 20 オンセット CDW オフセット 10 X~0.37 0 0 0.2 0.4 K濃度 x X K concentration 12 0.6 discussion-BKBO Bi(Pb) 6s electrons relate to TC? BaPbO3 KBiO3 BaBiO3 40 50 Ba1-xKxBiO3 (a) 40 電気抵抗率より決定 20 Tc (K) Tc (K) 30 on set オンセット オフセット off set 30 20 10 10 6s0.4 0 0 6s1 0.2 0.4 0.6 0 1 K concentration K濃度 xX (Ba,Rb)BiO3 (Ba,K)BiO3 (Ba,K)(Pb,Bi)O3 Ba(Pb,Bi)O3 (Sr,Rb)BiO3 (Sr,K)BiO3 (K,Bi)BiO3 (K,La)BiO3 Ba(Pb,Sb)O3 0.8 0.6 0.4 0.2 0 Bi(Pb) 6s軌道の電子数 Bi(Pb) 6s electrons TCmax~50K is limit ? 13 H. Matsuura and K. Miyake, J. Phys. Soc. Jpn. 81 (2012) 113705 discussion-BKBO Low carrier ~ 1018~19/cm3 Tc(K) My work Pb1-xTlxTe image X(at.%) TC~0.3K at X=0.3% VS 6s NaCl structure (space group Fm3m) Tl+ Tl3+ ・・・ ・・・ Tl+ Tl3+ -2e 0e 1 My work Ba Bi3+ Summary Bi5+ O ▪ 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 Bi3+ ⇔ Bi5+ Tl1+ ⇔ Tl3+ High TCSC ? 1 Summary Thank you for your listening END appendix Theory of SC by VS C. Varma PRL(1988) U:intra-atomic repulsion parameter(Bi-Bi) t:hopping(Bi-O) V:intra-atomic repulsion parameter(Bi-O) Δ:level t≪Δ attraction-repulsion eliminate the flexibility of oxygen CDW SC ~ 1 – t4/z2|U|2V2 x 9x discussion-BKBO Phase diagram in Ba1-XKXBiO3(BKBO) 40 BaBiO3 (a) TC~30K at X=0.37 Ba1-xKxBiO3 40 電気抵抗率より決定 20 10 50 Tc (K) Tc (K) 30 オンセット On set オフセット Off set No magnetic phase 0.2 30 0.4 0.6 K濃度 K concentration X x (Ba,Rb)BiO3 20 10 Low carrier 0 0 BaPbO3 KBiO3 0 1 (Ba,K)BiO3 (Ba,K)(Pb,Bi)O3 (Sr,Rb)BiO3 Ba(Pb,Bi)O3 (Sr,K)BiO3 (K,Bi)BiO3 (K,La)BiO3 Ba(Pb,Sb)O3 0.8 0.6 0.4 0.2 0 Bi(Pb) 6s軌道の電子数 Bi(Pb) 6s electrons Ba Bi3+ Bi5+ O Highest TC in oxide (without cuprate) 2 intriduction-BKBO BCS superconductivity? α TC∝ ∝(1/M)α M:isotope mass Physica B 296 (2001) 112}119 W.E. Pickett ? BCS theory × high TC Ba1-xKxBiO3 (a) 30 × Tc (K) Low-carrier 40 Electron-phonon interaction constant λ=0.2 電気抵抗率より決定 20 オンセット オフセット 10 0 0 0.2 0.4 K濃度 x X K concentration 0.6 6 New theory Valence Skipper relate to SC mechanism? discussion-BKBO Properties of Ba1-XKXBiO3(BKBO) U,V ⇒ larger Pm3m T(K) R3 CDW High TC??? I2/m Ibmm SC ~ 1 – t4/z2|U|2V2 x Ba Tilting & breathing Distortion Band gap Insul ator Structure Monoclinic 0 Bi3+ No? Tilting Semiconductor Metallic 13 Orthorhombic 0.1 Bi5+ O Cubic 0.37 0.5 × discussion-BKBO Theory of SC by VS C. Varma PRL(1988) U:intra-atomic repulsion parameter(Bi-Bi) t:hopping(Bi-O) V:intra-atomic repulsion parameter(Bi-O) Δ:level t≪Δ Bi3+ Bi5+ eliminate the flexibility of oxygen CDW SC x attraction-repulsion ccccccccc AF SC 9 Heavy electron system xdiscussion-BKBO Bi+3 Bi+5 charge density wave(CDW) state q Bi5+ Bi3+ Bi5+ Bi3+ Bi5+ Bi3+ Bi5+ Bi3+ R T (K) AF AF AF ++ SC SC SC CDW Hole or electron dope (high TC SC) Pressure (heavy electron system) SC ~ 1 – t4/z2|U|2V2 AF SC Heavy electron system x x 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 ( ) Summary 1.BKBO SC ,which has VS in the origin ,appearing condition 1.nearing CDW (due to VS) Ba Bi3+ Bi5+ O 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 2.PbTlTe Summary 同位体効果 TC∝(1/M)αj Properties of Ba1-XKXBiO3(BKBO) K dope ↓ Hall dope + K Ba2+ Ionic radii (Å) 1.64 1.61 Incommensurate CDW 40 and suppression of structural distortion Bi5+ O Tcmax=30K 電気抵抗率より決定 20 オンセット on set オフセット off set 10 Ba Bi3+ 30 K substitution Tc (K) Temperature Ba1-xKxBiO3 (a) 0 0 X~0.37 0.2 0.4 0.6 K濃度 x K concentration X 2 discussion-BKBO 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。 What is charge density wave(CDW)? K+ Ba2+ Bi3+ Bi5+ Ionic radii (Å) 1.64 1.61 1.03 0.76 5 Introduction-VS 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 "Tilting" and "Breathing" distortion ▪ "Breathing" ▪"Tilting" 5 Introduction-VS 同位体効果 No-tilt sample (thin film) Distortion Tilting & breathing Band gap Insul ator Structure Monoclini c 0 No? Tilting Semiconductor Metallic Cubic Orthorhombic 0.1 0.37 0.5 × 5 Summary arge density X q Bi5+ Bi3+ Bi5+ Bi3+ Bi5+ Bi3+ Bi5+ Bi3+ ρ(μΩ) R TC~11K BaPb0.8Bi0.2O3 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
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