Nodal s-wave superconductivity in BaFe 2 (As,P) 2

Transcription

1 Nodal swave superconductivity in BaFe 2 (As,P) 2 Taka Shibauchi Department of Physics Kyoto University

2 Collaborators K. Hashimoto M. Yamashita Y. Matsuda S. Kasahara T. Terashima H. Ikeda Y. Nakai K. Ishida Kyoto Univ., Japan I. Vekhter Louisiana State Univ. A.V. Vorontsov Montana State Univ. Penetration depth, Thermal conductivity Crystal growth, Transport Band Calculation NMR Thermal conductivity (theory) A. Carrington A. Serafin A.I. Coldea Univ. of Bristol, UK K. Cho R. Prozorov Ames Lab. T. Shimojima S. Shin T. Yoshida A. Fujimori Univ. of Tokyo, Japan G.R.Stewart J.S. Kim P.J. Hirschfeld Univ. of Florida Penetration depth, dhva Penetration depth ARPES Specific heat

3 Outline 1. Introduction Possible gap structures in Febased superconductors 2. Isovalent substitution system BaFe 2 (As,P) 2 Phase diagram and quantum critical point 3. Evidence for line nodes Penetration depth, thermal conductivity, NMR 4. Determination of the nodal structure ARPES, specific heat, angle dependent thermal conductivity 5. Summary

4 Possible gap functions q he Nodeless s ± Γ hole Γ hole s (s ) (k)= ー Σ q V(q) (kq)/2e kq X Interband nesting electron X electron Large χ(q) V(q) (kq) (k) < 0 Sign change Folded BZ (122) Mechanism of the superconductivity? spinfluctuation mediated pairing I.I. Mazin et al. PRL (08) K. Kuroki et al. PRL (08) PRB(09) A.V. Chubkov et al.prb (08) S. Graser et al. NJP (09) H. Ikeda JPSJ (08,09) K. Seo et al. PRL(08) F. Wang et al. PRL (09) orbital fluctuation (phonon) H. Kontani, S. Onari, PRL (10) T. Yildirim PRL (08) F. Kruger et al. PRB (09) Y. Yanagi et al. PRB (10)

5 Possible gap functions Folded BZ (122) Nodeless Nodal q he s ± Γ hole electron X d Γ hole q ee X electron Large χ(q) hole (kq) (k) < 0 Sign change electron s (s ) Γ X electron nodal s q he Γ X electron S. Graser et al., PRB (2010); K. Suzuki et al., JPSJ (2011) electron hole hole q ee I.I. Mazin et al., PRB (2010).

6 Gap Structures in Ironbased Superconductors Nodeless Anisotropic(?) Nodal 1111 PrFeAsO 1y [1] SmFeAs(O,F) [2] LaFeAs(O,F) [3] NdFeAs(O,F) [3] LaFePO (T c ~6 K) [2,4,1] 122 (Ba,K)Fe 2 As 2 [1,5,6] Ba(Fe,Co) 2 As 2 (optimum) [5,4] Ba(Fe,Co) 2 As 2 (overdoped) [5] Ba(Fe,Ni) 2 As 2 [3] KFe 2 As 2 (T c ~4 K) [7,1] BaFe 2 (As,P) 2 (T c ~31 K) [1] 111 LiFeAs [3,8] 11 Fe(Se,Te) [9] Based on bulk measurements of low energy quasiparticle excitations; penetration depth (superfluid density), thermal conductivity and specific heat. [1] Kyoto, [2] Bristol, [3] Ames, [4] Stanford, [5] Sherbrooke, [6]British Columbia, [7] Fudan, [8] Tokyo, [9] Nanjing It is important to determine the nodal structure in hight c BaFe 2 (As,P) 2

7 Outline 1. Introduction Possible gap structures in Febased superconductors 2. Isovalent substitution system BaFe 2 (As,P) 2 Phase diagram and quantum critical point 3. Evidence for line nodes Penetration depth, thermal conductivity, NMR 4. Determination of the nodal structure ARPES, specific heat, angle dependent thermal conductivity 5. Summary

8 Superconductivity in BaFe 2 As 2 systems Mother compound BaFe 2 As 2 (AF Metal) T Ba(Fe 1y Co y ) 2 As 2 electron doping SC 50 SDW (Ba 1x K x )Fe 2 As 2 hole doping SC y x BaFe 2 (As 1x P x ) 2 S. Jiang et al. JPCM (09) Isovalent doping (Chemical Pressure)

9 T (K) ρ(t) =ρ 0 AT α exponent ρ xx (T) T α α SDW BaFe 2 (As 1x P x ) 2 T N θ nonfl x c θ x BaFe 2 (As 1x P x ) 2 FL 0 Superconductivity x m * /m e Quantum critical point at the end point of SDW T 0 T SDW T c α BaFe 2 (As 1x P x ) 2 very clean single crystals dhva observations in doped system At a critical doping value x c =0.33 close to the end point of SDW T c becomes maximun Hallmark of nonfermi liquid in the transport coefficients S. Kasahara et al., PRB (10). Weiss temperature θ (NMR) goes to zero Y. Nakai et al., PRL (10). Strong enhancement of effective mass m * (dhva) H. Shishido et al., PRL (10). These trends originate from the same many body interactions which give rise to superconductivity

10 Outline 1. Introduction Possible gap structures in Febased superconductors 2. Isovalent substitution system BaFe 2 (As,P) 2 Phase diagram and quantum critical point 3. Evidence for line nodes Penetration depth, thermal conductivity, NMR 4. Determination of the nodal structure ARPES, specific heat, angle dependent thermal conductivity 5. Summary

11 BaFe 2 (As 1x P x ) 2 (T c ~ 31 K, x=0.33) magnetic penetration depth K. Hashimoto et al., PRB 81, (R) (2010). Tlinear penetration depth in BaFe 2 (As 1x P x ) 2 (T c ~ 30 K) clearly indicates the line nodes in the gap. with line nodes Impurity induced DOS λ(t) ~ T 2 /(TT*) T*=1.3 K cf. clean YBCO T*~1 K

12 BaFe 2 (As 1x P x ) 2 (T c ~ 31 K, x=0.33) magnetic penetration depth

13 BaFe 2 (As 1x P x ) 2 (T c ~ 31 K, x=0.33) Thermal conductivity κ isovalent Thermally excited QPs κ 00 /T: Impurity induced QPs hole Luo et al. Kurita et al. Doppler shift Field induced QPs Finite κ 0 /T in the T 0 K limit Thermally excited QPs H 1/2 dependence of κ 0 /T Clear evidence for line nodes in BaFe 2 (As 1x P x ) 2

14 NMR in isovalent doped BaFe 2 (As 0.7 P 0.3 ) 2 and hole doped (Ba 0.6 K 0.4 )Fe 2 As 2 Hole doped (Ba 1x K x )Fe 2 As 2 Full gap Tlinear isovalent hole Nodal superconductivity with high T c (31 K) Isovalent substitution BaFe 2 (As 1x P x ) 2 Line node unconventional mechanism is involved Y.Nakai et al. PRB (2010) T 1 T becomes constant at very low temperature Residual DOS due to line node NMR results are consistent with the penetration depth and thermal conductivity

15 Outline 1. Introduction Possible gap structures in Febased superconductors 2. Isovalent substitution system BaFe 2 (As,P) 2 Phase diagram and quantum critical point 3. Evidence for line nodes Penetration depth, thermal conductivity, NMR 4. Determination of the nodal structure ARPES, specific heat, angle dependent thermal conductivity 5. Summary

16 Gap structure of hole bands probed by Laser ARPES for BaFe 2 (As 0.65 P 0.35 ) 2 Hole band T. Shimojima et al. Science (2011). U. Tokyo Group 3 hole FSs around Zpoint Full gap in all three hole bands around Zpoint exclude the dwave symmetry

17 Specific heat vs Thermal conductivity K. Hashimoto et al., PRB (10). Specific heat C/T H H 1/2 component is less than 5% of the total specific heat Thermal conductivity J.S. Kim et al. PRB (10). κ/t H 1/2 H 1/2 component is more than 30% of the total thermal conductivity

18 K. Hashimoto et al., PRB (10). Specific heat vs Thermal conductivity Specific heat C/T H hole slow v F (heavy mass, large DOS) electron fast v F (light mass, small DOS) Thermal conductivity Hole J.S. Kim bands et al. PRB are (10). fully gapped κ/t H (consistent 1/2 with ARPES) Line nodes in the electron bands contributions of red parts in electron bands < 5% > 30%

19 Thermal conductivity in rotated H Doppler shift E (k, r) = E(k) v s (r) v F Fourfold oscillation, minima for H // node theory I.Vekhter et al K.Maki et al P.Thalmeier et al H.Kusunose 2004 M.Udagawa et al T. Nakai et al L.Tewordt and Fay 2005 review Y. Matsuda et al. J. Phys. C 18, R705 (06) T. Sakakibara et al. JPSJ 76, (07) Quasiparticles are not generated at nodal locations where v F // H (v s v F =0) The shape of the Fermi surface is important to determine the detailed gap structure A.Vorontsov and I.Vekhter, PRL 96, (06) PRB 75, (07) Y. Nagai and N. Hayashi, PRL 101, (08) G.R. Boyd et al. PRB 79, (09)

20 Angular variation of thermal conductivity BaFe 2 (As 0.67 P 0.33 ) 2 κ(φ)=κ 0 κ 2φ κ 4φ κ 2φ =C 2φ cos2φ, κ 4φ =C 4φ cos4φ large 4fold oscillation C 4φ ~C 2φ large C 2φ large C 4φ large C 2φ H//b H//a M. Yamashita et al. arxiv:

21 Nodal structure in BaFe 2 (As 1x P x ) 2 nodal loop nodes in electron bands fully gapped hole bands orbital character Nodal swave (extended swave) superconductivity change at the with nodal loops at the nodal flat positions parts of electron sheets

22 Doping dependence of penetration depth

23 Symmetries in (Ba,K)Fe 2 As 2 and BaFe 2 (As, P) 2 T Distinct pairing states (with and without nodes) 150 appear in a 122 family of Febased superconductors. This is unique among superconductors. 100 y electron doping x Line nodes (nodal s) SC SDW SDW Full gap (s± or s) SC (Ba 1x K x )Fe 2 As 2 BaFe 2 (As 1x P x ) 2 Isovalent doping (Chemical Pressure) Line nodes (d hole or horizontal) doping x KFe 2 As 2

24 Summary Superconducting gap structure probed by λ, κ, C, NMR, and ARPES Nodal s state in BaFe 2 (As,P) 2. Presence of line nodes indicates that unconventional mechanism is involved in superconductivity. Nodal loops in electron sheets Superconducting gap structure is not universal in a 122 family of Febased superconductors.