Systematic As-NMR study on iron oxpnictides F-doped LaFeAsO Kitaoka Laboratory Hiroki Yamashita Reference : Y. Nakai et al., J. Phys. Soc. Jpn 77, 073701 (2008) Y. Nakai et al., cond-mat/arXiv:0810.3569v1 (2008) Contents Introduction ・ history of superconductivity. ・ Fe-based oxypnictide compound. ・ Motivation. NMR measurement Experimental results Summary History of superconductivity 1911 200 High-Tc cuprate metal Iron-based system Hg-Ba-Ca-Cu-O Transition temperature (K) 163 150 (at a suitable pressure ) Hg-Ba-Ca-Cu-O Tl-Ba-Ca-Cu-O Bi-Sr-Ca-Cu-O 100 Y-Ba-Cu-O SmO0.9F0.11FeAs 50 Pb Hg 0 1900 La-Ba-Cu-O Nb NbC 1920 1940 NbN MgB 2 NbGe 1960 Year 1980 1957 BCS theory (Bardeen Cooper Schrieffer) 1986 77 nitrogen temperature BCS limit Superconductivity was discovered . LaO0.89F0.11FeAs LaOFeP 2000 2020 High-Tc cuprate was discovered . 2006 Iron-based layered oxypnictide . cuprate : 銅酸化物 Iron-based oxpnictide compound Phase diagram LaFeAs(O1-xFx) 160 Charge reservoir layer LaFeAsO1-xFx 140 FeAs layer e- Charge reservoir layer TN , TC(K) 120 100 TN from μSR 80 40 20 0 0.00 F Electron dope TC from μSR AFM 60 ?? 0.04 SC 0.08 0.12 0.16 0.20 Nominal F content x (O2-→F-) H. Luetkens et al., arXiv:0806.3533v1 ・ Superconducting transition relates to a magnetic instability ?? AFM:反強磁性 SC:超伝導 Motivation x = 0 sample : mother material LaFeAs(O1-xFx) x = 0.04 sample locates near the boundary between the AFM and SC phase. x = 0.07 sample : under-doped region 160 LaFeAsO1-xFx 140 x = 0.14 sample : over-doped region 120 TN , TC(K) x = 0.11 sample : optimally-doped region 100 TN from μSR 80 TC from μSR AFM 60 40 20 0 0.00 SC 0.04 0.08 0.12 0.16 0.20 Nominal F content x H. Luetkens et al., arXiv:0806.3533v1 We show systematic As-NMR stud on these samples. NMR measurement(1) Example As : I = 3/2 m= -3/2 m=±3/2 Energy Energy = m= -1/2 = m= +1/2 = m=±1/2 m= +3/2 Zeeman splitting Quadrupole splitting m= -3/2 HZ>>HQ Energy H = H Z + HQ = = = m= -1/2 m= +1/2 m= +3/2 NMR measurement(2) m= -3/2 Energy = = = m= -1/2 m= +1/2 m= +3/2 Echo Intensity second-order perturbation into the calculation E 1 1 2 2 1 1 2 2 1 3 2 2 Spin-lattice relaxation time T1 E external magnetic field E m=-1/2 m=1/2 m=-1/2 2Δ m=1/2 E Zeeman splitting Excitation 1 T5 T1 relaxation E m=-1/2 conduction electron m=1/2 1/T1 proportional to density of states. 1 T3 T1 1 e k bT T1 Experimental result(1) LaFeAsO ρ(mΩ・cm) 9 TN 6 3 The x=0 sample does not exhibit superconductivity. 0 1/T1(s-1) 12 6 0 0 50 200 150 100 Temperature(K) 250 300 *TN : antiferromagnetic transition temperature LaFeAsO is an itinerant antiferromagnet with TN~142K. Experimental result(3) X=0.14 sample does not exhibit superconductivity in H~9.89T. Recent theoretical 1/T1∝T3 Shape of gap ARPES measurement Penetration depth measurement 1/T1∝T3 inconsistent Line node Nodeless SC gap?? Fully gaped S± state with impurity effect Y. Nagai, et al., arXiv:0809.1197 (2008) H. Ding, et al., Europhys. Lett. 83, 47001 (2008). T. Kondo, et al., Phys. Rev. Lett. 101, 147003 (2008). K. Hashimoto, et al., arXiv:0806.3149 (2008). Experimental result(2) LaFeAs(O0.96F0.04) nonmetallic behavior We did not find a huge increase of 1/T1. The magnetic anomaly becomes weakened upon F-doping. TN The line width increases gradually below TN. 1/T1(s-1) 12 6 0 0 *TN : antiferromagnetic transition temperature *TC : superconducting transition temperature 50 100 150 200 250 300 Temperature(K) ▲LaFeAsO 1/T1 vs T Experimental result(4) At the x=0.07 sample , (T1T)-1 decrease rapidly. T* is not ascribed to a magnetic anomaly. Pseudogap behavior At x = 0.11 and x = 0.14 sample, pseudogap behavior is more pronounced. La2-xSrxCuO4 Pseudogap behavior is more pronounced in the underdope region. Summary ・Upon F-doping significant AFM fluctuations observed at x=0.04 are suppressed,and pseudogap behavior appears At x=0.11 and x=0.14. ・With existing experimental results,we have developed a phase diagram of LaFeAs(O1-xFx) .
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