NMR study on bismuth oxide superconductor BaPb x Bi 1-x O 3 H. Matsuura and K. Miyake, J. Phys. Soc. Jpn. 81 (2012) Kitaoka Lab. Takashi MATSUMURA K.Kumagai.et,al Physica C 274 (1997)

Contents Introduction NMR,NQR Result 137 Ba spectrum 137 Ba ・ 135 Ba T 1 Summary

T C max~30K Ba 1-X K X BiO spin Spin + orbital phonon BaPb X Bi 1-X O 3 T c max~12K 1975 History of Superconductors Introduction Valence skipper?

O (1s) 2 (2s) 2 (2p) 4 O 2- (1s) 2 (2s) 2 (2p) 6 Bi [Xe](4f) 14 (5d) 10 (6s) 2 (6p) 3 Bi 3+ Bi 5+ [Xe](4f) 14 (5d) 10 (6s) 2 (6p) 0 [Xe](4f) 14 (5d) 10 (6s) 0 (6p) 0 Skipping (ns) 1 state Valence skipper 結晶化学入門 遠藤忠 他 講談社サイエンティフィック、 wikipedia Valence skipper Introduction Anion Cation closed-shell structure stable structure Bi 4+ [Xe](4f) 14 (5d) 10 (6s) 1 (6p) 0 unstable structure

Negative U Introduction 6s 0 6s 1 6s 2 U S : Coulomb interaction Attraction U S <0

Candidates for Valence skipper SC Introduction Valence skipping effect? Nb 1-x Ta x Se 3 (Nb 3+,Nb 5+ ) AgSnSe 2 (Sn 2+,Sn 4+ ) Pb 1-x Tl x Te (Tl 1+,Tl 3+ ) BKBO,BPBO (Bi 3+,Bi 5+ ) ・・・・・・ ・・・・・・

Mother compound BaBiO 3 Perovskite structure BaPb x Bi 1-x O 3 Different valence Bi

Mother compound BaBiO 3 / BaPb x Bi 1-x O 3

Superconductivity of BaPb x Bi 1-x O 3 BaPb x Bi 1-x O 3 sc BaBiO 3 Bi [Xe](4f) 14 (5d) 10 (6s) 2 (6p) 3 Pb [Xe](4f) 14 (5d) 10 (6s) 2 (6p) 2 Hole doping BaPb 0.5 Bi 0.5 O 3 BaPbO 3 Hole doping CDW state

Samples sc Hole doping BaPb x Bi 1-x O 3 x=0.64 Semiconductor x=0.75 Superconductor x=0.91 Metallic BaBiO 3 CDW state BaPb x Bi 1-x O 3

Ex. I=1/2 I=1/2 H0＝0H0＝0 H 0 ≠0 m=+1/2 m=-1/2  ℏ H 0 Zeemann splitting ω=  H 0 NMR (Nuclear Magnetic Resonance) 核磁気共鳴 γ (gyromagnetic ratio) 磁気回転比 Nuclear Magnetic Resonance NMR,NQR NMR Intensity [a.u.] Frequency,H 0 ω,H 0

NMR,NQR NQR Intensity [a.u.] Frequency Nuclear Quadrupole Resonance Ex. Ba I=3/ m=±1/2 m=±3/2 hν Q quadrupole interaction

137 Ba NQR Spectrum of x=0.91: Metallic (T=1.6K) Spectrum

Nuclear Magnetic Resonance Ex. Ba I=3/2 NMR,NQR NMR Intensity ω EFG: 電荷分布 Real, broadening Ideal Real, broadening Ideal ω

Mother compound BaBiO 3 Perovskite structure BaPb x Bi 1-x O 3 Rotation

Ba site: tetragonal Spectrum (1,0,0) V XX V ZZ V YY

Spectrum Ba site: orthorhombic Crystal structure  Spectrum shape

137 Ba NMR Spectrum of x=0.91: Metallic x=0.91 Metallic Spectrum 20K One component tetragonal

137 Ba NQR Spectrum of x=0.64: Semiconductor (T=1.6K) Spectrum

137 Ba NMR Spectrum of x=0.64: Semiconductor 40% 60% + Spectrum 20K Two components tetragonal orthorhombic

Two components 30% 70% Ba NMR Spectrum of x=0.75: Superconductor Spectrum 20K tetragonal orthorhombic

Tetragonal phase x=0.91 Metallic x=0.64 Semiconductor x=0.75 Superconductor Tetragonal phase + Orthorhombic distortion Tetragonal phase + Orthorhombic distortion Spectrum T<350K Whole temperature Tetra Ortho

m=+1/2 m=-1/2 H0H0 time t M M(t) = M(∞)[1- exp(-t/T 1 )] Thermal equilibrium state M = M （ ∞ ） Relaxation M = M （ t ） Exited state M = M(0) = 0 t < 0t = 0t > 0 0 Ex. I=1/2 Ba T 1 Electronic spin, etc. Nuclear magnetic relaxation rate (T 1 -1 )

Ba T Ba/ 135 Ba-NMR T 1Q -1 T 1M -1 Valence skipping fluctuation? T 1 -1 =T 1M -1 +T 1Q -1 Nuclear magnetic relaxation rate (T 1 -1 )

x=0.91 Metallic x=0.75 Superconductor x=0.64 Semiconductor Ba T 1 small large EaEa

Samples sc Hole doping BaPb x Bi 1-x O 3 x=0.64 Semiconductor x=0.75 Superconductor x=0.91 Metallic BaBiO 3 CDWCDW fluctuation small large CDW fluctuation? Ba T 1

Pair hopping Bi Pb BaPb x Bi 1-x O 3 x=0.75 Pair hopping

Bi (6S) state Pair hopping BaPb x Bi 1-x O 3 x=0.75 Pair hopping

Bi (6S) state Pair hopping BaPb x Bi 1-x O 3 x=0.75 Negative U Pair hopping

Summary Superconductivity and a change of the structure are in a close relation. Nuclear relaxation mechanism was determined by charge fluctuations. The superconductivity in BPBO may be mediated by the valence skipping effect.