Bipartite magnetic parent phases in the iron oxypnictide superconductor

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1 M. Hiraishi 1, S. Iimura 2, K. M. Kojima 1,3*, J. Yamaura 4, H. Hiraka 1, K. Ikeda 1, P. Miao 1,3, Y. Ishikawa 1, S. Torii 1, M. Miyazaki 1, I. Yamauchi 1, A. Koda 1,3, K. Ishii 5, M. Yoshida 5,6, J. Mizuki 6, R. Kadono 1,3, R. Kumai 1,3, T. Kamiyama 1,3, T. Otomo 1,3, Y. Murakami 1,3, S. Matsuishi 4 and H. Hosono 2,4 SUPPLEMENTARY INFORMATION Bipartite magnetic parent phases in the iron oxypnictide superconductor 1 Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki , Japan 2 Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama, Kanagawa , Japan. 3 Department of Materials Structure Science, The Graduate University for Advanced Studies, Tsukuba, Ibaraki , Japan 4 Materials Research Center for Element Strategy, Tokyo Institute of Technology, Yokohama, Kanagawa , Japan. 5 SPring-8, Japan Atomic Energy Agency, Sayo, Hyogo , Japan 6 School of Science and Technology, Kwansei Gakuin University, Sanda, Hyogo , Japan * kenji.kojima@kek.jp Supplementary Information Contents Page Title 2-3 Hydrogen content and carrier doping in LaFeAsO 1-x H x. 4-5 Muon spin relaxation measurement. 6-7 Space group determination in the low-temperature phase. 8 X-ray powder patterns of LaFeAsO 0.49 H 0.51 at 300 K and 43 K. 9 Structure parameters of LaFeAsO 0.49 H 0.51 at 300 K and 43 K. NATURE PHYSICS 1

2 SUPPLEMENTARY INFORMATION Hydrogen content and carrier doping in LaFeAsO 1-x H x Hydrogen content The values of the analysed hydrogen content x(analysed) were determined by means of the thermal desorption spectroscopy instead of the previous method of the thermogravimetric mass spectroscopy reported in Ref. 7. The results are listed in Table S1. The losses of the hydrogen contents from the nominal values of x(nominal) increase with increasing x. One might care about some kind of increase of impurity in the heavier doping region because of the difference between the x(analysed) and the x(nominal). Indeed, only small percentage impurities of Fe and LaAs were observed even in the heavier doping region. This is probably because the external sources of the hydrogen, NaBH 4 and Ca(OH) 2 also serve as suppliers for extra oxygen, which suppresses the emergence of the impurity in LaFeAsO 1-x H x. Table S1 Nominal and analysed hydrogen content x in LaFeAsO 1-x H x. x(nominal) x(analysed) Carrier doping by hydrogen substitution X-ray absorption spectroscopy is a probe to determine element-selective electronic ground states that guides the clarification of the carrier doping via the substitution of hydrogen anion. Figure S1 shows Fe K-edge X-ray spectra of LaFeAsO 1-x H x, measured on the beam line BL11XU at SPring-8. The spectra were measured by the partial fluorescence yield method of the Kβ 1,3 emission. The prepeaks, indicated by arrows, are sensitive to the electronic structure due to direct 1s-3d quadrupole transitions to the unoccupied Fe 3d hybridized with As 4p states S1. The intensities decline systematically with doping the hydrogen, corresponding to the decrease of the density of the unoccupied electronic states by electron-doping. Moreover, we performed Hall coefficient measurements in LaFeAsO 1-x H x (x = ). The estimated electron concentrations develop from cm -3 (x = 0.04) to cm -3 (x = 0.51) 2 NATURE PHYSICS

3 SUPPLEMENTARY INFORMATION with doping the hydrogen S2. The details will be reported elsewhere. These experimental results therefore pronounce the clear electron doping by the substitution from the oxygen O 2- to the hydrogen H -. Figure S1 X-ray absorption spectra near the Fe K-edge of LaFeAsO 1-x H x at room temperature. The spectra are normalised to the atomic absorption away from the absorption edge. NATURE PHYSICS 3

4 SUPPLEMENTARY INFORMATION Muon spin relaxation measurement Significant damping of the muon spin precession There is an apparent conflict between the inhomogeneous property in the μsr experiments and the commensurate magnetic structure in the neutron study. In order to explain the conflict, one might consider an incommensurability beyond the resolution limit of the neutron diffraction and/or a short-range magnetic order. However, the magnetic wave vector can be estimated at q o = (0, 1+ε, 0) with ε < based on the orthorhombic indices from the high-resolution data of the neutron diffraction. Moreover, the magnetic Bragg peaks can be described as the well-defined resolution limited. Hence, these findings demonstrate fairly the commensurate and long-range magnetic order. There is the other possibility intrinsic to the dopant; that is, randomly distributed H atoms give rise to a slight spatial variation of the magnitude of magnetic order. Klauss et al. reported clear muon spin precession signal with the commensurate stripe-type antiferromagnetic order in the undoped LaFeAsO 22. While, the significant damping of μsr spectra was observed in the 3% doped LaFeAsO 0.97 F S although the magnetic peak in the neutron diffraction is still commensurate S4. The inconsistent results in the lower as well as the heavier doping regions presumably come from the different experimental probes on a microscopic scale such as the μsr measurement and on a macroscopic scale such as the neutron diffraction measurement. The slight modulation of the magnitude field derived from the dopant triggers the damping of the muon spin precession regardless of the carrier homogeneously doped in FeAs layer as described in the previous section. Our preliminary Hartree potential and dipolar field calculations to clarify a local magnetic field on a muon site advocate the above explanation. The dipolar field at the stable position of the implanted muon in x = 0.5 exhibits higher gradient than that in x = 0, which implies that the muon in crystal is more sensitive to the dopant in the AF2 magnetic structure. Coexistence of magnetism and superconductivity The competition/coexistence of magnetism and superconductivity is the distinctive feature of 4 NATURE PHYSICS

5 SUPPLEMENTARY INFORMATION unconventional superconductivity. In this issue, the characteristic spatial scale of the coexistence is the important point. The microscopic-scale sensitive tool, μsr measurement, is suited for the investigation of the volume fraction of the magnetic and superconducting phases with high reliability. For instance, the magnetic volume fractions of Ba 1-x K x Fe 2 As 2 obtained from μsr measurement reach 100% even in the superconducting phase, indicating the emergence of the microscopic coexistence S5. While, the magnetic volume fractions in the present compound decrease with increasing the superconducting (non-magnetic) volume fraction in the coexistence state. We can roughly estimate the minimum size of the superconducting domain, based on the extent of the dipolar field of the magnetic moment of 1.2 μ B in the magnetic domain and the detectable internal field of 1 mt, at ca. 2 nm, as reported in Sanna et al S6. Moreover, the chemical inhomogeneity is probably not related to the origin of the present coexistence because a large broadening in the X-ray profile is needed to explain the chemical origin however it is not observed even in the heavier doping region as can be seen in the high-temperature profiles of Fig. S2a, b. It is therefore suggested that the magnetism and superconductivity do not coexist on the microscopic scale but the probable mesoscopic scale in LaFeAsO 1-x H x (x = ). NATURE PHYSICS 5

6 SUPPLEMENTARY INFORMATION Space group determination in the low-temperature phase We discuss the space group in the advanced structural-ordered phase on the bases of the group-subgroup relation. We can provide the possible orthorhombic space groups, Pmmn, Cmme, Pmm2, Pmn2 1, Cmm2, Aem2, P , and C222, within the subgroups of the high-temperature one P4/nmm S7, taking account of the splitting of the tetragonal 220 T peak. Any monoclinic distortion was not observed in the high-resolution synchrotron radiation experiments. Moreover, in the low-temperature phase, neither an additional peak nor a broadening of h00 T peaks was observed; the former excludes Pmm2, Cmm2, P , and C222, the latter excludes Pmmn and Pmn2 1 accompanied by the expansion or contraction of the lattice along the <100> axis. Thus, most probable space groups are Cmme with the inversion symmetry and Aem2 without the inversion symmetry, that are the orthorhombic-cell with the diagonal distortion along the <110> of the tetragonal-cell. Here, we calculate the structure factor of LaFeAsO 0.5 H 0.5 for Cmme and Aem2 with the aim of rationalizing the observed intensities in Fig. S2. The simplified structure factors F of the orthorhombic 400 O and 040 O reflections in Cmme, corresponding to the 220 T reflection in the tetragonal phase, are estimated: F(400 O ) = F(040 O ) = 4f(La) + 4f(Fe) + 4f(As) + 2f(O), where the f denotes the atomic structure factor, the anomalous scattering factors, and the contribution of the hydrogen are neglected. Thus, the intensities of the two peaks should be equivalent except for the Lorentz-polarization factor, which is in good agreement with the experimental result in Fig. S2a at x = 0 as previously confirmed 19,S8. While, the structure factors of the orthorhombic 040 O and 004 O reflections in Aem2 are estimated: F(040 O ) = 4f(La) + 4f(Fe) + 4f(As) + 2f(O), and F(004 O ) = 4f(La) + 3.8f(Fe) + 3.9f(As) + 2f(O) + 1.2if(Fe) 1.0if(As) 0.1if(O), where the tetragonal c-axis is transformed into the orthorhombic a-axis. The different values in Aem2 can be explained by the emergence of the imaginary part in only the F(004 O ) with the loss of the inversion symmetry. This is in good agreeable to the difference of the 040 O and 004 O intensities in the advanced structural-ordered phase as indicated in Fig. S2b. As a 6 NATURE PHYSICS

7 SUPPLEMENTARY INFORMATION consequence, Aem2, belonging in the polar point group, is a unique solution to the space group in the AF2 phase. Figure S2 X-ray profiles of the (2, 2, 0) T reflections for x = 0 and 0.51 with the wavelength of λ = Å. The single peaks (green dotted line) at the high-temperature split in two (blue solid line) at the low-temperature with the tetragonal-orthorhombic transitions. a, In x = 0, the low-temperature structure was confirmed to be Cmme as previously reported 19,S8 ; the intensities of the two split peaks (red solid line) should be equivalent. b, The different intensities of the split peaks (red solid line) in the low-temperature for x = 0.51 can be explained by the loss of the inversion symmetry in Aem2. NATURE PHYSICS 7

8 SUPPLEMENTARY INFORMATION Figure S3 X-ray powder patterns of LaFeAsO 0.49 H 0.51 at 300 K and 43 K obtained by the synchrotron radiation source (λ = Å). Experimental data points are shown by crosses, and the line through them is a fit by Rietveld analysis assuming a mixture of two phases, LaFeAsO 0.49 H 0.51 and LaAs. Resultant structural parameters are listed in Table S2. 8 NATURE PHYSICS

9 SUPPLEMENTARY INFORMATION Table S2 Refined structure parameters of the atom sites, the atomic coordinates, and the isotropic displacement parameters at 300 K and 43 K for LaFeAsO 0.49 H 0.51 are listed in the upper and lower panel, respectively. The displacements of the Fe and As atoms estimated by the present data across the structural transition are illustrated in the inset of Fig. 4. T = 300 K, tetragonal, P4/nmm (No. 129, origin 2), a = (3), c = (1) Å. Atom Site x y z U iso (10-2 Å 2 ) La 2c 1/4 1/ (9) 0.71(4) Fe 2a 3/4 1/ (4) As 2c 1/4 1/ (2) 0.68(3) O 2b 3/4 1/4 1/2 0.6 (3) R wp = 1.41%, R p = 0.95%, R F = 1.01% R wp, R p, and R F are residuals of observed and calculated intensities. T = 43 K, orthorhombic, Aem2 (No. 39), a = (1), b = (1), c = (1) Å. Atom Site x y z U iso (10-2 Å 2 ) La 4c (9) 3/ (2) Fe 4a (2) 0.34(3) As 4c (1) 3/ (2) 0.28(3) O 4b 1/ (11) 0.20 R wp = 1.53%, R p = 1.01%, R F = 0.62% The calculated U iso parameter of oxygen from 300 K was used. NATURE PHYSICS 9

10 SUPPLEMENTARY INFORMATION References S1. Joseph, B. et al. A study of the electronic structure of FeSe 1 x Te x chalcogenides by Fe and Se K-edge x-ray absorption near edge structure measurements. J. Phys. Condens. Matter 22, (2010). S2. Iimura, S. et al. Unusual Hall effect of iron oxypnictide LaFeAsO 1-x H x. unpublished. S3. Carlo, J. P. et al. Static magnetic order and superfluid density of RFeAs(O,F) (R = La; Nd; Ce) and LaFePO studied by muon spin relaxation: Unusual similarities with the behavior of cuprate superconductors. Phys. Rev. Lett. 102, (2009). S4. Huang, Q. et al. Doping evolution of antiferromagnetic order and structural distortion in LaFeAsO 1 x F x. Phys. Rev. B 78, (2008). S5. Wiesenmayer, E. et al. Microscopic coexistence of superconductiviy and magnetism in Ba 1-x K x Fe 2 As 2. Phys. Rev. Lett. 107, (2011). S6. Sanna, S. et al. Magnetic-superconducting phase boundary of SmFeAsO 1 x F x studied via muon spin rotation: Unified behavior in a pnictide family. Phys. Rev. B 80, (2009). S7. Wondratschek, H. & Müller, U. Ed., International Tables for X-ray Crystallography, Vol. A1, Kluwer Academic Publishers, 2004, p S8. Nomura, T. et al. Crystallographic phase transition and high-t c superconductivity in LaFeAsO:F. Supercond. Sci. Technol. 21, (2008). 10 NATURE PHYSICS