Slide 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) 11370581 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 Slide 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 Slide 3 Introduction 1 T C max~30K Ba 1-X K X BiO 3 1988 spin Spin + orbital phonon Spin/valence BaPb X Bi 1-X O 3 T c max~12K 1975 Slide 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=510 21 /cm 3 T C ~30K at X=0.37 On set Off set No magnetic phase Slide 5 Previous study of BKBO system3 introduction-BKBO BKBO Bi(Pb) 6s electrons Slide 6 Parent material BaBiO 3 (BBO)1 discussion-BKBO Ionic radii ( ) Ba 2+ 1.61 Bi 3+ 1.03 Bi 4+ (6s) 1 Bi 5+ 0.76 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) 11370581 2+ 2- Band calculation Slide 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 Slide 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 ( ) K+K+ 1.64 Ba 2+ 1.61 K dope Hole dope X~0.37 K concentration X on set off set T c max~30K T(K) solubility limit Slide 9 Properties of Ba 1-X K X BiO 3 (BKBO)4 discussion-BKBO R3 I2/m Ibmm Pm3m solubility limit 0.1 0 0.37 0.5 Insul ator Semiconductor Metallic MonoclinicOrthorhombic Cubic Tilting & breathing Tilting No? Distortion Structure Band gap T(K) SC Slide 10 Superconductivity gap in BKBO5 discussion-BKBO 2/kT C =3.50.5 Full gap Week-coupling SC Slide 11 BCS superconductivity? Electron-phonon interaction constant =0.2 Low carrier=510 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 M:isotope mass T C (1/M) BCS Slide 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) 11370581 Slide 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) :level tt eliminate the flexibility of oxygen ccccccccc attraction-repulsion 9 discussion-BKBO Bi 3+ Bi 5+ Slide 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 Ks 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 ? Slide 15 T 1Q -1 (s -1 ) 1000/T(1/K) X=0.5 X=0.4 X=0.3 10 discussion-BKBO 137 Ba/ 135 Ba-NMR ( 137 / 135 )=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) 209-220 BaPb X Bi 1-X O 3 eQ : Quadrupole moment : 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) Slide 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 Slide 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 Slide 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) 11370581 Slide 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 Slide 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 ? Slide 21 Thank you for your listening END Slide 22 appendix Slide 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) :level tt eliminate the flexibility of oxygen attraction-repulsion x 9 discussion-BKBO Slide 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 Slide 25 BCS superconductivity? BCS theory Electron-phonon interaction constant =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 M:isotope mass T C (1/M) Slide 26 0.1 0 0.37 0.5 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 Slide 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) :level tt eliminate the flexibility of oxygen ccccccccc attraction-repulsion 9 discussion-BKBO Bi 3+ Bi 5+ Slide 28 Bi 3+ Bi 5+ Bi 3+ Bi 5+ Bi +3 Bi +5 charge density wave(CDW) state R q Slide 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 Slide 30 T K W exp(-1/J cf D( F )) T RKKY D( F ) J cf 2 Phase Diagram of HF system AFM : antiferromagnetism HF : heavy fermion state QCP : quantum critical point < ( ) (f)J Slide 31 Slide 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 Slide 33 T C (1/M) j Slide 34 Properties of Ba 1-X K X BiO 3 (BKBO) X~0.37 2 discussion-BKBO Temperature and K substitution suppression of structural distortion K concentration X on set off set Incommensurate CDW Ionic radii ( ) K+K+ 1.64 Ba 2+ 1.61 K dope Hall dope T c max=30K Slide 35 CDW 2. -U Ag 1. Slide 36 What is charge density wave (CDW)? 5 Introduction-VS Ionic radii ( ) K+K+ 1.64 Ba 2+ 1.61 Bi 3+ 1.03 Bi 5+ 0.76 Slide 37 - - C. Varma PRL(1988) Slide 38 "Tilting" and "Breathing" distortion "Breathing" "Tilting" 5 Introduction-VS Slide 39 Slide 40 No-tilt sample (thin film) Slide 41 0.1 0 0.37 0.5 Insul ator Semiconductor Metallic Monoclini c Orthorhombic Cubic Tilting & breathing Tilting No? Distortion Structure Band gap 5 Summary Slide 42 X Charge density Slide 43 Bi 3+ Bi 5+ Bi 3+ Bi 5+ R q BaPb 0.8 Bi 0.2 O 3 T C ~11K () Slide 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