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Antiferromagnetic spin fluctuation and Superconductivity

Antiferromagnetic spin fluctuation and Superconductivity. Y. Nakai et al., PRB 87, 174507 (2013). Kitaoka Lab. M1 Y usuke Yanai. Contents. Introduction ・ History of Superconductivity ・ AFM and Superconductivity ・ Character of AFM spin fluctuation Analysis on spin fluctuations

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Antiferromagnetic spin fluctuation and Superconductivity

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  1. Antiferromagnetic spin fluctuation and Superconductivity Y. Nakai et al., PRB 87, 174507 (2013) Kitaoka Lab. M1 Yusuke Yanai

  2. Contents • Introduction • ・ History of Superconductivity • ・ AFM and Superconductivity • ・ Character of AFM spin fluctuation • Analysis on spin fluctuations • ・Ba(Fe1−xCox )2As2 • ・BaFe2(As1−xPx )2 • Result & Discussion • Summary

  3. introduction History of Superconductivity 1900 1920 1940 1960 1980 2000 2020 Year metal superconductor 200 metal heavy fermion system electron-phonon interaction high-Tccuprate 163 Hg-Ba-Ca-Cu-O iron-based system under high pressure （ ） 150 Heavy fermion superconductor Hg-Ba-Ca-Cu-O Tl-Ba-Ca-Cu-O Bi-Sr-Ca-Cu-O 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 FeAs LaO F PuCoGa5 Nb Ge 0.11 0.89 Nb Iron-based high-Tc superconductor Pb CeCu2Si2 NbN LaOFeP Hg NbC 0

  4. introduction AFM and SC Temperature valence transition HF q = 0 ferromagnetism valence/spin fluctuation Tc～ 1K AFM SC Pressure TS Temperature Iron-based TN spin/orbital fluctuation Tc～ 50K q = Q (π , π) antiferromagnetism AFM SC Doping fraction Cuprate Temperature spin fluctuation Tc～ 100K AFM q : wave vector SC Doping fraction

  5. introduction • Character of AFM spin fluctuation • Spin fluctuation parameter T0 and TA χ’’(Q,ω) q=Q (π , π) χq ω Temperature q = Q (π , π) antiferromagnetism AFM SC Doping fraction q

  6. introduction • Character of AFM spin fluctuation • Spin fluctuation parameter T0 and TA χ’’(Q,ω) ∝TA 1/ξ q=Q (π , π) χq ω Temperature q = Q (π , π) antiferromagnetism ∝T0 AFM SC ΓQ Doping fraction q ξ : magneticcorrelation length ΓQ : characteristic energy

  7. motivation • Relationship between T0and Tc , TA and TC Cuprate HF HF Cuprate Tc∝ TA3/4T01/4 ？ Higher T0 , TA enhance pairing interaction Iron- based Higher Tc

  8. BaFe2As2 • crystal structure of BaFe2As2 Co-dope (electron-doping) P-dope (isovalent-doping) • Ba(Fe1-xCox)2As2 • BaFe2(As1-xPx)2 F. L. Ning et al. , PRL 104, 037001(2010) Y. Nakai et al., PRB 81, 020503R(2010)

  9. Calculations ofT1 Release the energy Spin lattice relaxation time T1 (Dynamic information) ∝ T1 1/T1T is generally expressed by in SCR theory Time constant T1 ∝ χQ∝ Energy transfer Electronic spin system Nuclear spin system

  10. ❶ • Analysis on spin fluctuations in Ba(Fe1−xCox )2As2 ( 1/T1T )obs. loc. ( q independent ) 1/T1T (sec-1K-1) → loc. Temperature (K) K = Kspin + Kchem(0.15%) loc. K (%) Kspin Kchem (0.15%) Temperature (K)

  11. Analysis on spin fluctuations in Ba(Fe1−xCox )2As2 ❷ For QCP(θ =0 ), = const. QCP 0.05 < x < 0.08

  12. Analysis on spin fluctuations in Ba(Fe1−xCox )2As2 ❸ determine y0, T0, and TA y0 : parameter characterizing the closeness to QCP 1/T1T y0 NMRexperiment γ T0 specific heat experiment χ(Q,ω) TA neutron scattering experiment

  13. Analysis on spin fluctuations in Ba(Fe1−xCox )2As2 ❹ 1/T1 Electric resistivity (Ba(Fe0.92Co0.08)2As2) SCR calculation SCR calculation experiment experiment very good agreementwith the experimental data SCR theory

  14. Analysis on spin fluctuations in BaFe2(As1−xPx )2 ❶ • Analyze BaFe2(As1-xPx)2 • in the same way For QCP, = const. QCP x ～ 0.33

  15. Analysis on spin fluctuations in BaFe2(As1−xPx )2 ❷ 1/T1 Electric resistivity ~T 1 experiment SCR calculation experiment SCR calculation away from the QCP crossover to a Fermi-liquid-like T 2 very good agreement with the experimental data SCR theory

  16. Result &Discussion • QCP and Tc max • Ba(Fe1-xCox)2As2 • BaFe2(As1-xPx)2 QCP x ～ 0.33 QCP x ～ 0.06 Tc max x ～ 0.3 Tc max x ～ 0.06 QCP ≃ Tc max

  17. Result &Discussion TcvsT0 χ’’(Q,ω) 0.06 (OPT) Iron-based HF Cuprate 0.08 ω SC ＆ AFM ∝T0 HF Iron-based Cuprate Tc～ 1K Tc～ 50K Tc～ 100K

  18. Result &Discussion • TcvsTA Cuprate Iron-based HF χq SC ＆ AFM ∝TA HF Iron-based Cuprate Tc～ 1K Tc～ 50K Tc～ 100K q q=Q (π , π)

  19. Result &Discussion • TN and TC Result TN Cuprate Iron-based Cuprate Iron-based HF HF Temperature AFM PQ : antifferromagnetic moment per magnetic atom at T=0K SC Doping fraction

  20. Summary • NMR and resistivity data of Ba(Fe1-xCox)2As2, • BaFe2(As1-xPx)2 are simulated by SCR theory. • The concentration of maximum Tc corresponds to • that of AF QCP. AFM fluctuation plays an important role for SC. • Along with HF and cuprate, for iron-based • superconductors, higher T0 and TA give higher Tc. • The physics of iron-based may be closely related to the physics of HF and cuprate.

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