Kitaoka lab. Takayoshi SHIOTA M1 colloquium N. Fujiwara et al.,
Phys. Rev. Lett. 111, 097002 (2013) K. Suzuki et al., Phys. Rev.
Lett. 113, 027002 (2014) S. IIMURA et al., Nature Commun. 3, 943
(2012)
introduction Superconductivity Superconductivity is caused by
forming electron pairs
Slide 4
introduction Superconductivity Electron-phonon interaction Spin
or valence fluctuation Spin or valence fluctuation Spin fluctuation
Pairing glue ? ?
Slide 5
introduction Iron-based superconductors Ln Ae A Ln =La, Ce, Pr,
Nd, Gd, Tb, Dy, Er, Y Ae =Ba, Sr, Ca, Eu A =Li, Na Ae 4 M 2 O 6 Fe
2 Pn 2 Ln Fe Pn O Ae Fe 2 Pn 2 A Fe Pn Fe Ch 42622111112211111 T c
max =46KT c max =56KT c max =38KT c max =31K T c max =13K Distance
between Fe-planes Long Short Long Distance between FePn-planes Fe
Pn Ch M Ae O
Slide 6
introduction FePn tetrahedral structure and T c h Pn Fe Pn
Mizuguchi et al. Supercond. Sci. Technol. 23 (2010) 054013. = 109.5
C. H. LEE et al. J. Phys. Soc. Jpn., Vol. 77, No. 8 h Pn ~ 1.38
(Regular tetrahedron)
Slide 7
introduction Electronic state Phase diagram The correlation
between magnetic fluctuation and superconductivity?
AF:antiferromagnetic SC:superconductivity
Slide 8
introduction Electron doping effect k electron E Electron
doping Electron doping Worse nesting Phase diagram Band structure
Fermi- surface (,0) hole FF
Slide 9
Sample LaFeAs(O 1-x H x ) x=0.36 T c =36K x=0.36 T c =36K
x=0.08 T c =29K x=0.08 T c =29K x 0.04
75 As-NMR of LaFeAs(O,H) AFM fluctuations revive with the
approach of the second AFM phase Worse nesting Fe As La (O,H)
Experiment
Slide 18
Superconductivity in LnFeAs(O,H) SC1 SC2 large small Bond angle
36K 47K 56K 55K SC1 : unique to La-1111 SC2 : universally to
Ln-1111 Fe As La (O,H) Ln a c La : Double domes Ln(La) : Single
dome Experiment
Slide 19
Theory Origin of SC2 in LaFeAs(O,H) Fe As Fe t1t1 t2t2 dxy t 2
>t 1 in the largely doped regime
Slide 20
Theory Fe As Fe large small Bond angle Electron doping t1t1
t2t2 dxy Origin of SC2 in LaFeAs(O,H)
Slide 21
Theory Fe As The next nearest hopping within the dxy orbitals
causes the enhancement of the spin fluctuation t 2 >t 1 in the
largely doped regime As Fe dxy t1t1 t2t2 Origin of SC2 in
LaFeAs(O,H)
Slide 22
Theory SC1 SC2 large small Bond angle 36K 47K 56K 55K Fe As
large small The next nearest hopping may be a key factor for
appearance of higher T c dome Bond angle t2t2 Superconductivity in
LnFeAs(O,H)
Slide 23
Summary These NMR and theoretical studies were performed in
LaFeAs(O,H). A new antiferromagnetic phase was discovered on
further electron doping. The spin fluctuations revive with the
approach of the second AFM phase. The next nearest hopping of
electrons within dxy orbital may be a key factor for this revival
of spin fluctuation and appearance of higher T c dome. As Fe
dxy