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(Color online) Fermi surfaces of iron based superconduc­tors8) (a) and pairing interaction mediated by spin uctua­
tions1) (b).

Fig. 3ªC­©©ç»ÝÜÅLÍÈ_ÆµÄc_³êÄ«(Color online) Superconducting and magnetic transition
122: T
temperatures (Tc and TN) of Ba(Fe1_xTx)2As2, (T_Co, Ni, Cu)4,16). (a): Plotted as functions of the number ofsubstituted transition­metal atoms per Fe site, x. (b): Plot­ted as functions of nominal extra electron number per Fe sitex , 2x, and 3x for Co_, Ni_, and Cu_
122, respectively.

½1) BXshç¬}îÌ´`±@\ÅÍCdqÊãÆz[ÊãÅ´`±p[^ D ªðÏ¦é s}gªàÁÆà©RÉÀ»³êémFig. 2(b)nBXshç¬ÌêCËÍÝìpªN[p[ÎÌÚÜÆµÄ­­

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Co_122Ì ARPES ÌÊÅÍCtF~ÊÌÌÏªuóÔÌ´`±MbvÉm[hÉÂ¢ÄCäXÌúËõð·´qÉæÁÄ³ê½dqÊ¾¯Ï»µCtF~Êp¢½ ARPES Éæé¤¬Ê14,15)ðSÉðàµC´`ª W bho h f É] ¢¬ ·µÄ ¢é17) Bµ ©

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µCs¨´qðüúIÉÀ×½´iqð¼èµ½§xÄÖ_iDFTjÌvZÉæéÆ18) Ch[v³ê½dqÍÙÆñÇª Co, Ni, Cu ÈÇÌu·´qTCgÌüèÉ

160  úËõ May 2013 Vol.26 No.3

ÁW ¡ Sn´`±ÌÌúËõ ARPES ðp¢½¤ÌiWF³fu·øÊÆ´`±Mbvm[hFig. 4(Color online) Angle­integrated photoemission spectra of
Ni_122 [panel (a)] and Cu_122 [panel (b)]. Partial densityof states for Ni and Cu 3d orbitals obtained by band­struc­ture calculation18) are also plotted. Shaded area shows theenergy region dominated by Ni and Cu 3d­derived states.
Fig. 5(Color online) ARPES intensity plot in ka_
kz momentum
space for Ni_
122 and Cu_122 obtained by hn­dependent(a4): Hole and electron FSs
ARPES measurements. (a1)_(b4): Hole and electron FSs for Cu_122.
for Ni_122. (b1)_
kF points of the hole and electron FSs are plotted by black
dots. The ARPES intensity plots have been symmetrizedwith respect to symmetry lines.

Fig. 6(Color online) Hole and electron FS volumes from the122, and Cu_122
ARPES data of BaFe2As2, Co_122, Ni_plotted as functions of the nominal extra electron number.
(a): Hole FS volume nh. (b): Electron FS volume nel. (c):Total FS volume nel_nh. Black dashed line shows the behav­ior (nel_nhextra electron per Fe/T site) expected from therigid­band model. BaFe2As2 and Co_122 data are taken from
Ref. 17. (d) Tc and TN of Ba(Fe1_xTx)2As2 (TCo, Ni,Cu)4,16) plotted as functions of the total FS volume nel_nh
evaluated by ARPES. Panel (e) is a magnied plot of Tc.

ªzµÄ¨èCÕðIÈdqªìéohÉdqðlßÄ
ä­CWbhohfÆµ·éæ¤ÉÝ¦éBêûÅC¯lÌ´iqÌvZÅtF~ÊÌ`óðß½ÊÅÍCtF~ÊÉÍÜê½dqÍm~iÈdqª¾¯ÁµÄ¢é±Æª¦³êÄ¨è19) CWbhohfðxµÄ¢éBSn´`±ÌÌdq\¢É¨¢ÄCJÚà®u·ªÇÌöxWbhohfÉÄÍÜéÌ©G

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éªdÈÁÄ¢éBêûCCu 3d RÌ\¢Í Fe 3d Ì\¢æèCÍé©É[­ 4_5 eV tßÉ©çê
éB±êÍCu·µ½JÚà®´qÌ|eVªC´qÔªiÞÉÂêÄ[­ÈÁÄ¢é±Æð¦µÄ¢éB¾çê½XyNg`óÍC´iqÌohvZÅ¾çê
½óÔ§xÆÇ­êvµÄ¢é18)BÉCdC`±Éñ^·étF~ÊtßÌdq\¢ð²×é½ßÉCãNõGlM[ðÏ»³¹Äªèµ½
ka_kz ½ÊÌtF~Ê}bvÌÊð Fig. 5 É¦·B±±Å ka Í ab ÊÉ½sÈ^®ÊÅCkz Í c ²ûüÌ^®ÊÅéBBZ æ«EÌ Z _ñèÉÍíÉ 2 Ìz[Êª¶ÝµÄ¢éªCBZ æÌ G _tßÍ Ni Zxðã°éÆtF~ÊªÈ­ÈèCz[Êª 3 ³IÈ`óð¦µÄ¢é±Æªª©éBêûCX _tßÌdqtF
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·Ìêà¯lÉ Ni ZxÌÁÆÆàÉ nel_nh ªÁµúËõ May 2013 Vol.26 No.3  161Ä¢éªCWbhohfÌ¼üæè­µºÉ¸êÄ¢é±Æªí©éB³çÉ Cu u·ÅÍ Ni u·æèÍé©ÉºÉ¸êÄ¨èCCo, Ni, Cu ÆiÞÉÂêÄCWbhohfª¬è§½È­ÈÁÄ¢é±Æª¾ç
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3d ÆêÉÈÁÄohðgÝC³ê½dqÍ»ÌohÉüéBêûCNi, Cu Ì 3d O¹Í Fe 3d O¹ÆÌGlM[|eV·ªå«­CFe 3d O¹ª`¬·é`±ohÉdqðµÉ­­ÈèCFe 3d oh©
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ARPES ©ç©Ïàçê½ nel_nh ªdC`±ðS¤³¡

Fig. 7(Color online) Fermi surfaces of BaFe2(As1_xPx)2 (x0.38)
observed by ARPES23). (a), (b) ARPES intensity at EF
mapped in the kX_
kY plane taken at several photon energies.
The Brillouin zone boundary is shown by blue lines. Red dots
indicate kF positions determined by the peak positions of
momentum distribution curves. (c) Fermi surface mappingkz plane obtained by changing the photon energy.
in the k//_(d) Band­structure calculation for x0.4.

Fig. 8(Color online) Line nodes in the superconducting gap ofiron­based superconductors predicted by theoretical studies.
(a) horizontal node in the hole FS around the Z point25). (b)Loop­like nodes in the electron FSs27).

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162  úËõ May 2013 Vol.26 No.3

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èmFig. 8É[vóÉm[hªüéÆ¢¤ñÄ27) ª(b)nCpxªðM`±¦ÌÀ±ÊÍCdqÊÉm[hªüéàðxµÄ¢é28) B_IÉÍ½m[hÆ[vóm[hÍC»ê¼êÙÈéN[p[ÎUÌvZXÅ¶¶é½ßC¼Òª¤¶·éÂ\«àéBàÁÆà¼ÚIÉ^®ÊóÔÌîñª¾çêé ARPES ÅÍC±êÜÅÉ[U[ãNõâúËõðp¢Ä´`±MbvªÏ
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IÉJ¢Ä¢élqªÏª³ê½29) B[U[ÌãNGlM[ hn7 eV Í Z _tßÉÎµÄ¢é½ßC±ÌÊÍ½ m[hàÆ eêÈ¢ ÊÅé BêûC

Zhang et al. ÍúËõðp¢ÄChn35 eV Å½m[hªÏª³ê½±ÆðñµXshç¬}îÌ_ðxµÄ¨è30) Cf[^ÔÌêvª©çêÄ¢È¢Ìª»óÅéB

Fig. 10

Fig. 9(Color online) Superconducting gap observed on the holeFSs in BaFe2(As1_xPx)2 (x0.30, Tc30 K) around the Zpoint (hn35 eV). (a) Temperature dependence of the sym­
metrized ARPES spectra in kX direction with a circularly
polarized light. Fermi momentum kF s are indicated by ar­rows in the data at T100 K. (b1) (b2) EDCs at kF for theouter and inner hole FSs. Gaps open not only for the data be­
low Tc but also for the higher temperatures, indicating pseu­
dogap behavior.

(Color online) Superconducting gap observed on the hole FSs with various kz in BaFe2(As1_xPx)2 (x0.30). (a)Correspondence between incident photon energy, kz and the three­dimensional hole FSs (blue curves). (b) (c)Second derivative plots of the ARPES spectra around the G and Z points. Around the G point, three QP disper­
sions are clearly resolved. (d_f) Symmetrized EDCs at kF points in the G_
X direction taken below Tc. Verticalbars indicate the gap energy. (g) Gaps estimated in panels d_f are plotted as a function of hn.

úËõ May 2013 Vol.26 No.3  163

Fig. 11

(Color online) Superconducting gap anisotropy observed on the electron FSs around the X point in BaFe2(As1_x
Px)2 (x0.30, Tc30 K) taken at hn40 eV. (a) Fermi surface mapping using a circularly polarized light. The
Fermi angle is dened so that the direction from X to G is uFS0. (b) EDCs at kF taken below Tc (T13 K) andcompared with gold spectra. (c) (d) EDCs at kF taken below (T13 K) and above (T35 K) Tc for the innerand outer FSs. Vertical bars indicate the crossing energy between the spectra below and above Tc. (e) (f) Energyof the crossing point for the inner and outer FSs are plotted as a function of Fermi surface angle uFS.

ª©éBFig. 9(b1)(b2)ÌtF~ÊãÌGlM[ªzÉÈÁÄ¢é¾ë¤©BFig. 11(a)ÉCãNGlM[40ÈüiEDCj©çàª©éæ¤ÉCà¤CO¤Ì¢¸ê

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®SÉÂ¶éêÍÏª³êÈ©Á½ªCARPES ÅÍ kzûüÌpxªð\ªé½ßCéöx kz ûüÌîñªÁW ¡ Sn´`±ÌÌúËõ ARPES ðp¢½¤ÌiWF³fu·øÊÆ´`±Mbvm[h4. ÜÆßÆ¡ãÌW]
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Wbhohf©çÌ¸êªFßçêCJÚà®Ì|eVÌ[³ÉæÁÄdqóÔªÏíÁÄ­é±Æª¾ç©ÉÈÁ½BARPES ÉæÁÄ©Ïàçê½³¡ÌLFig. 12 (Color online) SC gap D for all the FSs of BaFe2(As1_xPx)2.
Momentum dependence of the D for x0.30 deduced fromthe ARPES result. Color scale represents the magnitude of
the SC gap. Loop­like nodes or gap minima appear near therim of the inner electron FSs.

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éB

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såwåw@ClÔÉÂ«w¤ÈCy³ö
E­mail: yoshida.teppei.8vkyoto­u.ac.jpêåFÅÌ¨Cõdqªõmªðn
2002Nåwåw@wn¤Èm
ÛöC¹CmiwjB2002N_2004N
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2013N¯åw@wn¤È³B2013
Næè»EBoc^êYåwåw@CHwn¤ÈCú{wpU»ïÁÊ¤õE­mail: idetaap.t.u­tokyo.ac.jpêåFÅÌ¨Cõdqªõmªðn
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166  úËõ May 2013 Vol.26 No.3

¡X~åwåw@Cwn¤ÈC³ö
E­mail: fujimoriphys.s.u­tokyo.ac.jpêåFÅÌ¨CúËõªõmªðn
1978Nåwåw@wn¤ÈCm
ÛöC¹CwmB1978N_1988N³@
Þ¿¤¤õÉåC¤¯B1988N_
1999N åw w ³öB 1999N_
2007Nåwåw@VÌæn¬Èw¤È³öB2007Næè»EBÁW ¡ Sn´`±ÌÌúËõ ARPES ðp¢½¤ÌiWF³fu·øÊÆ´`±Mbvm[hProgress in the synchrotron radiation ARPES
studies of iron­based superconductors:
Element substitution eects andsuperconducting gap nodes
Teppei YOSHIDA

Graduate School of Human and Environmental Studies,
Kyoto University, Sakyo­ku, Kyoto 606_8501, Japan

Shin­ichiro IDETA

Department of Applied Physics, University of Tokyo,
Bunkyo­ku, Tokyo 113_8656, Japan

Atsushi FUJIMORI

Department of Physics, University of Tokyo,
Bunkyo­ku, Tokyo 113_0033, Japan

Abstract

After 5 years has passed from the discovery of iron­based superconductors, the characteristic
electronic structure has been claried and clues to understanding the mechanism of the supercon­
ductivity have been found. While the similarities with the cuprate high­T c superconductors havebeen emphasized from the beginning of the research in iron­based superconductors, dierent
aspects from the cuprates have also been claried. In this article, we will introduce recent angle­
resolved photoemission studies with synchrotron radiation which revealed the element substitu­
tion eects and the superconducting gap nodes in iron­based superconductors.

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