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Superconducting gap structure in BaFe 2 (As 0.7 P 0.3 ) 2 revealed by ARPES

Superconducting gap structure in BaFe 2 (As 0.7 P 0.3 ) 2 revealed by ARPES. T.Yoshida et.al. a rxiv : 1301.4818. T.Shimojima et.al. Science 332,564. Kitaoka Lab Masashi Miyamoto. ① Introduction ・ Iron-based Superconductors ・ BaFe 2 (As 1-x P x ) 2

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Superconducting gap structure in BaFe 2 (As 0.7 P 0.3 ) 2 revealed by ARPES

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  1. Superconducting gap structure in BaFe2(As0.7P0.3)2 revealed by ARPES T.Yoshida et.al. arxiv : 1301.4818 T.Shimojima et.al. Science 332,564 Kitaoka Lab Masashi Miyamoto

  2. ① Introduction ・Iron-based Superconductors ・BaFe2(As1-xPx)2 ・Fermi surfaces (FSs) ・Motivation ②Experiments ・Angle-Resolved Photoemission Spectroscopy (ARPES) ③ Results ・ARPES results ・Comparison to theoretical calculation. ④ Summary Contents

  3. Introduction Iron-based Superconductors 1900 1920 1940 1960 1980 2000 2020 Year 200 2006 metal heavy fermion system Iron-based high-Tc superconductor high-Tc cuprate 163 Hg-Ba-Ca-Cu-O iron-based system under high pressure （ ） 150 Hg-Ba-Ca-Cu-O Tl-Ba-Ca-Cu-O Bi-Sr-Ca-Cu-O 100 Transition temperature (K) Y-Ba-Cu-O 77 SmO F FeAs 50 0.9 0.11 MgB2 La-Ba-Cu-O LaO F FeAs PuCoGa5 Nb Ge 0.11 0.89 Nb Pb CeCu2Si2 NbN LaOFeP Hg NbC 0

  4. Iron-based Superconductors Introduction 1111 122 111 11 Fe As FeSe LiFeAs LaFeAsO BaFe2As2 Tc max = 55K Tc max = 38K Tc max = 18K Tc max = 8K Each system has FeAs (FeSe) layer

  5. Introduction • BaFe2As2 Ba1-yKyFe2As2 Ba(Fe1-zCoz)2As2 T hole-doping electron-doping Stripe AFM SC y SC z 0

  6. Introduction • BaFe2(As1-xPx)2 Motivation Substitution P for As ⇒ iso-valent doping ⇒ chemical pressure Substitution : 置換 iso-valent : 等価な

  7. Introduction • BaFe2(As1-xPx)2 Motivation X=0.3 (This work) AFO : Anti Ferromagnetic-orthorhombic SC : Superconductivity (tetragonal) PT : Paramagnetic-tetragonal orthorhombic : 斜方晶の tetragonal : 正方晶の

  8. Introduction • BaFe2(As1-xPx)2 The origin of Superconductivity? Motivation z Degenerated 3d-orbital ⇒ orbital degrees of freedom Orbital fluctuation ⇔Superconductivity ? Anti-ferromagnetic spin fluctuation ⇔ Superconductivity ? fluctuation : 揺らぎ degenerated : 縮退した

  9. Introduction ky kx Superconductivity mediated by anti-ferromagnetic spin fluctuation Sign-changing of Superconducting gap Fermi Surfaces Single band (cuprate) Multi band (Iron-based) Δ>0 Node( Δ= 0 ) Δ<0 Δ<0 ？ Δ>0 Nodal gap node : 超伝導ギャップが０になる点 Δ : 超伝導ギャップ Cuprate : 銅酸化物

  10. Introduction kz ky electron Fermi Surface (Iron-based) kx hole Band structure Two dimensional structure like a cylinder Full gap Some of these have nodes ?

  11. Introduction • Existence of line node • in BaFe2(As1-xPx)2 Motivation Magnetic penetration-depth ①Where nodes exist ? Thermal conductivity ② SC gap structure NMR (Nuclear Magnetic Resonance) Observe the Fermi Surfaces of BaFe2(As0.7P0.3)2 directly by ARPES Magnetic penetration-depth : 磁場侵入長 ＮＭＲ : 核磁気共鳴

  12. ARPES Photo-emisson spectroscopy Experiments Photo-emissonspectroscopy (PES) E detect Vacuum level (Ev) Fermi level (EF) Φ仕事関数 Energy conservation photoelectric effect EB: Binding Energy DOS PES provides information of Density of states. Photo emission spectroscopy : 光電子分光

  13. Experiments ARPES Angle-resolved photo-emission spectroscopy P// Vacuum photon P⊥ θ p⊥ Sample surface detector p// Sample Momentum conservation in surface parallel direction ARPES reveals Band dispersions and Fermi surface picture. Angle-resolved photo-emission spectroscopy : 角度分解型光電子分光 dispersion : 分散

  14. Result example 5 1 θFS ① hole FSs kz ky kx Γ Isotropic SC gap Isotropic : 等方的　⇔ anisotropic : 異方的

  15. Results example ① hole Fermi Surfaces kz ky kx No line nodes

  16. Results ②electron Fermi Surface A clear anisotropy is not identified Anisotropic gap !

  17. Results ＋ Momentum dependence of the SC gap － Hole FSs K.Suzuki et.al. JPSJ-80-013710 isotropic gap (no node) anisotropic gap node onlySpin-fluctuation-mediated mechanism

  18. Results Calculation with consideration of both spin and orbital fluctuation experiment theory Loop-like node Theoretical calculation Inner electron FS Inner electron FSs : anisotropic gap (loop node) Hole FSs : isotropic gap (no node)

  19. Summary In BaFe2(As0.7P0.3)2 ・Hole FSs have no node Motivation ・Inner electron FS has gap anisotropy and loop-like node ・Both spin fluctuations and orbital fluctuations may contribute to the superconductivity

  20. Thank you for your listening.

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