ARPES studies of Fe pnictides: Nature of the antiferromagnetic-orthorhombic phase and the superconducting gap

Transcription

1 Novel Superconductors and Synchrotron Radiation: state of the art and perspective Adriatico Guest House, Trieste, December 10-11, 2014 ARPES studies of Fe pnictides: Nature of the antiferromagnetic-orthorhombic phase and the superconducting gap Atsushi Fujimori University of Tokyo Nature of the AFM-orthorhombic (AFO) phase and the nematic phase : Band folding versus C 4 symmetry breaking Superconducting gap anisotropy

2 Collaborators Photoemission expt K. Koshiishi, L. Liu, H. Suzuki, J. Xu, K. Okazaki, T. Shimojima (U of Tokyo), T. Yoshida (Kyoto U), S. Ideta (TUS) K. Ono, H. Kumigashira (KEK-PF), Y. Ohta, S. Shin (ISSP) M. Hashimoto, D. Lu, Z.-X. Shen (Stanford U) A. Ino, M. Arita, H. Anzai, H. Namatame, M. Taniguchi (Hiroshima U) Samples K. Kihou, C.-H. Lee, T. Ito, Y. Tomioka, A. Iyo, H. Eisaki (AIST) S. Uchida (U of Tokyo) Y. Matsuda, S. Kasahara, T. Terashima (Kyoto U), T. Shibauchi (U of Tokyo) T. Kobayashi, S. Miyasaka, M. Nakajima, S. Tajima (Osaka U) Theory R. Arita (RIKEN), H. Ikeda (Ritsumeikan U) H. Kontani, T. Saito (Nagoya U.) S. Onari (Okayama U)

3 Outline Nature of the AFM-orthorhombic (AFO) phase and the nematic phase : Band folding versus C 4 symmetry breaking Superconducting gap anisotropy

4 Phase diagram of Fe-based superconductors Electron doping Hole doping Antiferromagnetic Orthorhombic (AFO) phase 0.0 Doped electron x N. Ni et al., PRL Doped holes x/2 per Fe atom M. Rotter et al., Angew. Chem. Int. Ed. 08

5 Phase diagram of Fe-based superconductors AFO SC

6 Magneto-structural transition and possible electronic nematic phase Antiferromagnetic -orthorhombic (AFO) phase BaFe 2 (As 1-x P x ) 2 T N =T S AFO phase Q. Huang et al., PRL 08 S. Kasahara et al., Nature 13

7 Folded Fermi surfaces of BaFe 2 As 2 in the AFO phase Hole FS Electron FS Z Electron FS Hole FS Electron FS Z F. Ma et al., Front. Phys. China 10

8 Folded Fermi surfaces of BaFe 2 As 2 in the AFO phase LDA calculation Hole FS Electron FS Z Z : Dirac cone Z Z T. Terashima et al., PRL 11

9 Folded Fermi surfaces of BaFe 2 As 2 in the AFO phase by ARPES LDA adjusted to de Haas-van Alphen experiment Z2 Hole FS C1 Electron FS Z X/Y Z1 D2 : Dirac cone Y/X Z X/Y ARPES for k z ~ Z, detwinned T. Terashima et al., PRL Dirac cone Cut D2 k y ( /a) Momentum(π/a) D D2 X -1 Z2 Z 0 k x ( /a) Y 1 k y ( /a) h = 63 ev T =20 K b Y Z a Z1 C k x ( /a) X 1.0 E-E F (ev) ε electron pocket Cut Z0 Momentum(π/a) C1 K. Koshishi et al.

10 Folded Fermi surfaces of BaFe 2 As 2 in the AFO phase revealed by ARPES Present result Correct ed α/β? Electron pocket δ Hole pocket? ε Dirac cone K. Koshiishi et al. M. Yi et al., PNAS 11

11 C 4 symmetry breaking in the AFO and nematic phases of BaFe 2 (As 1-x P x ) 2 Magnetic torque measurements Magnetic torque X-ray diffraction C 2 C 4 resistivity S. Kasahara et al., Nature 12

12 Anisotropic band dispersions in the AFO phase of BaFe 2 As 2 C 4 symmetry breaking 0 Z Y 0 Z X E-E F (ev) -0.1 d xz E-E F (ev) -0.1 d xz k y ( /a) k x ( /a) ARPES for k z ~ Z, detwinned k y ( /a) X Y k y ( /a) Y X D2-1 Z2 Z 0 k x ( /a) 1 h = 63 ev T =20 K b a Z1 C1 Z k x ( /a) 1.0 K. Koshishi et al.

13 Persistence of the anisotropic band dispersions above T N,S Ba(Fe 0.95 Co 0.05 ) 2 As 2 X- Y anisotropy T N T S T* M. Yi et al., PNAS 11

14 Persistence of the anisotropic band dispersions above T N,S BaFe 2 (As 0.93 P 0.07 ) 2 X- Y anisotropy T. Shimojima et al., PRB 14

15 C 4 symmetry breaking and band folding in Fe-based superconductor: Possible antiferro-orbital order 1.5 k y ( /a) X D1 X Z1 Z Y BaFe 2 (As 1-x P x ) k x ( /a) K K T N =T S E - E F (e V) E - E F (e V) AFO phase ferro-orbital order (q=0 )? Antiferro-orbital order (q 0 )? Angle (deg) Angle (deg) T N,S = 142 K K. Koshishi et al.

16 Possible antiferro-orbital order below T* O xz antiferro-quadrupole (AFQ) order? AFQ order = Antiferro-orbital + Ferro-orbital order Elastic constant C 66 H. Kontani et al., RB 11 q 0 AF orbital order T* M. Yoshizawa et al., JPSJ 12

17 Summary AFO and nematic phases Folded electron and hole Fermi surfaces in the AFO phase revealed by ARPES are in almost perfect agreement with those deduced from the Subunikov-de Haas measurements. Not only C 4 symmetry breaking but also band folding survive above T N, S, suggesting the persistence of an antiferro-orbital order above T N, S up to T*.

18 Outline Nature of the AFM-orthorhombic (AFO) phase and the nematic phase : Band folding versus C 4 symmetry breaking Superconducting gap anisotropy

19 Nodeless s + superconducting gap in Fe pnictides Superconducting gap of K 0.4 Ba 0.6 Fe 2 As 2 s + -wave superconductivity Electron Fermi surfaces - - /a + Hole Fermi surfaces /a /a Order parameter (k) = 0 (cosk x a + cosk y a)/2 H. Ding et al., Europhys. Lett. 08 K. Kuroki et al., PRB 09

20 Superconductivity with line nodes in BaFe 2 (As 1-x P x ) 2 Phase diagram Penetration depth S. Kasahara et al., Nature 13 K. Hashimoto et al., PRB 10

21 Superconductivity with line nodes in SrFe 2 (As 1-x P x ) 2 Phase diagram Penetration depth as grown annealed annealed as grown annealed T. Kobayashi et al., PRB 13 J. Murphy et al., PRB 13

22 Line nodes in order parameter according to spin-fluctuation mechanism high Pnictogen height h Pn low Hole FS d yz,zx (d z2 ) Electron FS d xy d yz,zx Hole FS d xy K. Kuroki et al., PRB 09 h pn

23 Superconducting gap on hole Fermi surfaces of BaFe 2 (As 0.65 P 0.35 ) 2 and SrFe 2 (As 0.65 P 0.35 ) 2 BaFe 2 (As 0.65 P 0.35 ) 2 h =7 ev, k z ~ Z SrFe 2 (As 0.65 P 0.35 ) 2 h =23 ev k z ~ Z FS independent, T. Shimojima et nearly al., Science isotropic 11 FS dependent, H. nearly Suzuki isotropic et al. SrFe 2 (As 0.65 P 0.35 ) 2

24 Line nodes in order parameter according to spin-fluctuation mechanism high Pnictogen height h Pn low Hole FS d yz,zx (d z2 ) Electron FS d xy d yz,zx Hole FS d xy K. Kuroki et al., PRB 09 h pn

25 Possibility of horizontal line nodes in spin-fluctuation mechanism + Hole FS - S. Graser et al., PRB 10. K. Suzuki et al., JPSJ 11

26 Superconducting gap on hole Fermi surfaces: Combined spin and orbital fluctuations FS1 FS2 FS1 FS2 FS3 FS3 SC gap S. Onari and H. Kontani, PRL 12 T. Saito, S. Onari, H. Kontani, PRB 13

27 k z dependence of the superconducting gap on hole Fermi surfaces of BaFe 2 (As 0.70 P 0.30 ) 2 Outer FS k z dependence Closes at k z ~ Z Y. Zhang et al., Nat. Phys. 12

28 k z dependence of the superconducting gap on hole Fermi surfaces of BaFe 2 (As 0.70 P 0.30 ) 2 Outer FS Middle FS Inner FS k z dependence Nearly k z independent T. Yoshida et al., Sci. Rep. 14

29 k z dependence of the superconducting gap on hole Fermi surfaces of SrFe 2 (As 0.65 P 0.35 ) 2 Z Z as-grown annealed Gap minimum around k z ~ Z Gap opens around k z ~ Z H. Suzuki et al.

30 Line nodes in order parameter according to spin-fluctuation mechanism high Pnictogen height h Pn low Hole FS d yz,zx (d z2 ) Electron FS d xy d yz,zx Hole FS d xy K. Kuroki et al., PRB 09 h pn

31 Four-fold symmetry of thermal conductivity in magnetic fields in BaFe 2 (As 1-x P x ) 2 Angular dependence M. Yamashita et al., PRB 11

32 Possible line nodes in superconducting gap on electron Fermi surfaces Vertical line nodes Loop-like line nodes M. Yamashita et al., PRB 11. Loop-like line nodes I. Mazin et al., PRB 10

33 Superconducting gap on electron Fermi surfaces of BaFe 2 (As 0.70 P 0.30 ) 2 Isotropic Y. Zhang et al., Nat. Phys. 12

34 Superconducting gap on electron Fermi surfaces of BaFe 2 (As 0.70 P 0.30 ) 2 h =40 ev Gap magnitude T c =30 K Inner electron FS Anisotropy T. Yoshida et al., Sci. Rep. 14

35 Superconducting gap on electron Fermi surfaces of SrFe 2 (As 0.65 P 0.35 ) 2 outer Inner As-grown Annealed Nearly isotropic H. Suzuki et al.

36 Summary of ARPES experiments on gap anisotropy in isovalent-substituted 122 systems Hole FS Electron FS BaFe 2 (As,P) 2 (x=0.30) Y. Zhang et al. ~ 0 at k z ~ Z isotropic (x=0.30, 0.38) (x=0.35) T. Yoshida et al. T. Shimojima et al. > 0 for all k z > 0 at k z ~ Z FS-independent anisotropic SrFe 2 (As,P) 2 (x=0.35) before annealing H. Suzuki et al. ~ 0 at k z ~ Z isotropic after annealing > 0 for all k z isotropic Ba(Fe,Ru) 2 As 2 (x=0.35) L. Liu et al. ~ 0 at k z ~ Z isotropic

37 Summary Superconducting gap Superconducting gap anisotropy is material, composition, and disorder dependent even in the limited number of isovalent P- and Ru-substituted systems: Hole FS: Gap minimum or no minimum around k z ~ Z. Electron FS: Isotropic or anisotropic.