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A = Ca, Sr , Ba

Superconductivity in system A Fe 2 ( As 1-x P x ) 2. Fe. As. A = Ca, Sr , Ba. Evolution from non-Fermi- to Fermi-liquid transport via isovalent doping in BaFe 2 (As 1− x P x ) 2 superconductors Kasahara et. al., Phys. Rev. 81, 184519(2010). Dulguun Tsendsuren Kitaoka Lab.

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A = Ca, Sr , Ba

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  1. Superconductivity in system AFe2(As1-xPx)2 Fe As A = Ca, Sr, Ba Evolution from non-Fermi- to Fermi-liquid transport via isovalent doping in BaFe2(As1−xPx)2 superconductors Kasahara et. al., Phys. Rev. 81, 184519(2010) DulguunTsendsuren Kitaoka Lab. Division of Frontier Materials Sc. Department of Materials Engineering Sc. Graduate School of Engineering Sc., Osaka Univ.

  2. Introduction 1900 1920 1940 1960 1980 2000 2020 Year History of Superconductivity 200 metal heavy fermion system Discovery of superconductivity 1911 high-Tccuprate 163 Hg-Ba-Ca-Cu-O iron-based system under high pressure （ ） 150 Hg-Ba-Ca-Cu-O Tl-Ba-Ca-Cu-O Heavy fermion superconductor Bi-Sr-Ca-Cu-O 1979 1986 100 Transition temperature (K) Y-Ba-Cu-O 77 High-Tccuprate superconductor 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 2006 CeCu2Si2 NbN LaOFeP Hg NbC 0 Iron-based high-Tc superconductor

  3. Introduction Iron-based Superconductors 42226 1111 122 111 11 Fe As Today’s talk Each system has FeAs layer

  4. AFe2As2 System Introduction CaFe2As2 SrFe2As2 BaFe2As2 CaFe2(As1-xPx)2 SrFe2(As1-yPy)2 BaFe2(As1-zPz)2 iso-valent doping Role of FeAs layer in 122 system

  5. Superconducting gap Introduction Full gap Nodal gap Density of State Density of State gap gap Energy Energy EFermi EFermi Spin-Lattice Relaxation Rate (by NMR) Magnetic Penetration Depth Thermal Conductivity Specific Heat Spin-Lattice Relaxation Rate (by NMR) Magnetic Penetration Depth Thermal Conductivity Specific Heat

  6. Relaxation rate 1/T1 by NMR Introduction Releases the energy T1: spin-lattice relaxation time I Spin-Lattice interaction e nuclear spin electronic spin Energy Transfers in almost T1 time

  7. How to verify SC gap? Introduction Spin-Lattice Relaxation Rate (by NMR) Spin-Lattice relaxation time Nodal gap: Temperature Linear relation Full gap: Temperature Non-Linear relation

  8. Exp. Result Resistivity of BaFe2(As1-xPx)2 Resistivity: T0 Structure transition TSDW AFM Order TconSuperconductivity appears Resistivity reflects phase transition clearly as other transport properties

  9. Phase Diagram of BaFe2(As1-xPx)2 Exp. Result Transitions: Structure SDW onset Tc Bulk Tc At x = 0.26 Tcmax = 31 [K] Doping level (x) of P in BaFe2(As1-xPx)2

  10. Resistivity of BaFe2(As1-xPx)2 Exp. Result Resistivity: Fermi-liquid: Tc = 0[K] AFM fluctuation: Tc = 31[K] Highest Tc is clearly related to AFM fluctuation (Non-Fermi-liquid)

  11. Fermi Surfaces vs. Doping Calculation BaFe2As2 Ba0.8K0.2Fe2A2 BaFe2P2 iso-valent doping (P at As) hole doping (K at Ba) Tcmax = 38[K] Tcmax = 31[K] 2D like FS 3D like FS Full gap Nodal gap Full gap shows higher Tc compared with Nodal gap With 3D like FSs, SC gap becomes Nodal gap

  12. CaFe2(As1-xPx)2 Exp. Result Fermi surfaces: Tcmax = 15 [K], at x = 0.05 Tetragonal (SC) c-Tetra. (NC) SC occurs in tetragonal structure In c-Tetra., FS changed into 3D SC disappears in c-Tetra

  13. Summary • Superconductivity occurs: • AFM fluctuation appears nearby high Tc SC region • With structural change (Orthorhombic to Tetragonal) • Fermi Surface is structure dependent. In most cases, SC occurs when FSs are like 2D • Essence of Full gap is one of promising key to increase Tc in Superconductivity

  14. Thank you for your attention

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