Transcript BaFe 2
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 Contents 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 Iron-based Superconductors Transition temperature (K) 200 2006 metal heavy fermion system high-Tc cuprate 163 Hg-Ba-Ca-Cu-O iron-based system 150 （under high pressure ） Hg-Ba-Ca-Cu-O Tl-Ba-Ca-Cu-O Bi-Sr-Ca-Cu-O 100 Y-Ba-Cu-O 77 50 MgB2 Pb Hg 0 1900 Nb NbC 1920 1940 La-Ba-Cu-O PuCoGa5 NbGe NbN CeCu2Si2 1960 Year Introduction 1980 2000 SmO 0.9F 0.11FeAs LaO 0.89F 0.11FeAs LaOFeP 2020 Iron-based high-Tc superconductor Introduction Iron-based Superconductors 122 1111 111 11 Fe As LaFeAsO BaFe2As2 LiFeAs FeSe Tc max = 55K Tc max = 38K Tc max = 18K Tc max = 8K Each system has FeAs (FeSe) layer Introduction BaFe2As2 T Ba1-yKyFe2As2 Ba(Fe1-zCoz)2As2 electron-doping hole-doping Stripe AFM y SC SC 0 z BaFe Motivation 2(As1-xPx)2 Introduction Substitution P for As ⇒ iso-valent doping ⇒ chemical pressure Substitution : 置換 iso-valent : 等価な BaFe Motivation 2(As1-xPx)2 Introduction 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 BaFe Motivation 2(As1-xPx)2 Introduction The origin of Superconductivity? z Degenerated 3d-orbital ⇒ orbital degrees of freedom Anti-ferromagnetic spin fluctuation ⇔ Superconductivity ? Orbital fluctuation ⇔Superconductivity ? fluctuation : 揺らぎ degenerated : 縮退した Introduction Fermi Surfaces Superconductivity mediated by anti-ferromagnetic spin fluctuation Sign-changing of Superconducting gap Single band (cuprate) ky Node ( Δ= 0 ) Δ>0 Δ<0 Δ<0 Multi band (Iron-based) ？ kx Δ>0 Nodal gap Δ : 超伝導ギャップ Cuprate : 銅酸化物 node : 超伝導ギャップが０になる点 Fermi Surface (Iron-based) Introduction kz ky electron kx hole Band structure Two dimensional structure like a cylinder Full gap Some of these have nodes ? Motivation Introduction Magnetic penetration-depth Existence of line node in BaFe2(As1-xPx)2 Thermal conductivity NMR (Nuclear Magnetic Resonance) ① Where nodes exist ? ② SC gap structure 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 ARPESPhoto-emisson spectroscopy Photo-emisson spectroscopy E Vacuum level (Ev) Fermi level (EF) h Experiments (PES) detect h Ek EB Energy conservation EB h Ek EB: Binding Energy photoelectric effect DOS PES provides information of Density of states. Photo emission spectroscopy : 光電子分光 Experiments ARPES Angle-resolved photo-emission spectroscopy P// Vacuum photon h h detector P⊥ θ Sample surface p⊥ Sample p// 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 Result ① hole FSs example θFS 5 1 kz ky Γ kx Isotropic SC gap Isotropic : 等方的 ⇔ anisotropic : 異方的 ① hole Fermi Surfaces Results example kz ky kx No line nodes ②electron Fermi Surface Anisotropic gap ! Results A clear anisotropy is not identified Momentum dependence of the SC gap ＋ isotropic gap anisotropic gap (no node) only Spin-fluctuation-mediated mechanism node Results Hole FSs － K.Suzuki et.al. JPSJ-80-013710 Results Theoretical calculation Calculation with consideration of both spin and orbital fluctuation experiment theory Loop-like node Inner electron FS Inner electron FSs : anisotropic gap (loop node) Hole FSs : isotropic gap (no node) Summary Motivation In BaFe2(As0.7P0.3)2 ・Hole FSs have no node ・Inner electron FS has gap anisotropy and loop-like node ・Both spin fluctuations and orbital fluctuations may contribute to the superconductivity Thank you for your listening.