Electronic inhomogeneity, magnetic order & superconductivity probed by NMR in cuprates and pnictides

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1 Electronic inhomogeneity, magnetic order & superconductivity probed by NMR in cuprates and pnictides Marc-Henri Julien Laboratoire de Spectrométrie Physique Université J. Fourier Grenoble I

2 Acknowledgments Grenoble High Magnetic Field Lab. : V. Mitrovic (postdoc), C. de Vaulx (undergrad), H. Mayaffre, M. Horvatic, C. Berthier LSCO ( * ) x=0.12 crystals: T. Suzuki & K. Yamada (Sendai) Pnictide crystals: G.F. Chen, J.L. Luo, N.L. Wang (IOP Beijing) ( * ) Earlier LSCO work with F. Borsa (Pavia & Ames) Crystals by C.T. Lin (MPI Stuttgart), A.Vietkin & A. Revcolevschi (Orsay)

3 NMR, a true local probe of electronic inhomogeneity Staggered magnetization around impurities in Haldane chain Electronic density modulated by out-of-plane (Na + ) electrostatic potential MHJ et al., F. Tedoldi et al., PRL 83, 412 (1999) Co 3+ Co 3.3+ Co 3.4+ (not actual pattern)

4 Ubiquitous SC-AF coexistence in correlated systems NMR contributions: CUPRATES PNICTIDES (this talk) Heavy fermions 2D organics 1D organics NMR review N.J. Curro S. Lefebvre et al., PRL (2000) I.J.Lee, S.E. Brown et al.

5 Hyperfine couplings in NMR Nucleus 139 La Nucleus 139 La 75 As dipolar interaction Transferred hyperfine interaction Electron d orbital Nucleus 63 Cu 57 Fe On-site Hyperfine interaction

6 139 La NMR in La 2-x Sr x CuO 4 ( , the second youth of LSCO)

7 Magnetic transition

8 Magnetic volume fraction? Incommensurate elastic signal Truly static or slow (<<1 mev) fluctuations? T N (30 K) > T g (20 K) 100% of the muons experience both spin freezing and superconductivity (for x<0.1)

9 Magnetic volume fraction 100% of the La nuclei experience spin freezing 1/T 1 (s -1 ) La NMR La 1.88 Sr 0.12 CuO T (K) At least one magnetic Cu within ~1 nm from each La Superconductivity? Bulk (from magnetization) Not seen in 139 La data Residual paramagnetic 63 Cu signal Nanoscale/microscopic coexistence

10 Revised phase diagram of LSCO La 2-x Sr x CuO 4

11 SC / AF (Cluster SG) coexistence S. Sanna et al., PRL (2004) YBa 2 Cu 3 O 6+x Panagopoulos PRB (2002) Niedermayer PRL (1998) Ohishi JPSJ (2005) Bi 2.1 Sr 1.9 Ca 1-x Y x Cu 2 O 8+y Y 1-x Ca x Ba 2 Cu 3 O 6 Ca 2-x Na x CuO 2 Cl 2

12 Disordervs. stripe physics

13 Inhomogeneous spin fluctuations Distribution of relaxation times T 1 distribution single T 1 Freezing temperature T g is inhomogeneous (onset=20 K, av=13 K)

14 Inhomogeneous magnetism / cluster spin-glass 1/T 1 (s -1 ) La La 1.88 Sr 0.12 CuO 4 PRB (2008) Progressive freezing of spin fluctuations BPP-type description T g is frequency (thus probe) dependent T (K) NMR Signal (a.u.) La 1.94 Sr 0.06 CuO 4 LSCO x= Cu NMR, H c T=290 K PRL (1999) 24 T 17 T AF clusters Inhomogeneous local magnetization in CuO 2 planes with strong staggered component K total (%) M.-H. J et al., PRL (1999)

15 Nanoscale doping inhomogeneity

16 Quenched disorder in La 1.88 Sr 0.12 CuO 4 Pristine : T c = 30 K Disordered : T c = 10 K 1/T 1 (s -1 ) pristine disordered Magnetic transition shifts to lower T Consistent with ~1% planar defects σ log Magnetic distribution mostly unaffected T (K)

17 LSCO conclusions Similarity with stripe ordered (LTT) materials indirect evidence of stripes in LTO Ordered stripe phase «Stripe glass» Nematic Electronic liquid crystal Electronic glass with Unidirectional domains Intrinsic disorder/inhomogeneity is obvious (but 1% of planar defects not dramatic) Disorder also in stripe ordered (LTT) materials Magnetic order coexists with superconductivity at the microscopic scale

18 Pnictide zoology

19 Ba(Fe 1.95 Co 0.05 ) 2 As 2 Ba(Fe 1-x Co x ) 2 As 2 SDW Full Meissner fraction Sharp transition T c = 15 K SC 4πχ (emu/cm 3 ) 0-1 x = 0.05 Ba(Fe 1.95 Co 0.05 ) 2 As 2 H=10 Oe, ab T (K)

20 75 As NMR in Ba(Fe 1.95 Co 0.05 ) 2 As 2 MHJ et al., arxiv: ρ ab (µω m) S C SDW 0 I NMR (a.u) 2 Paramagnetic resonance position 1 S C SDW Skin effect T (K) 100% of the 75 As nuclei experience magnetic order

21 75 As NMR in Ba(Fe 1.95 Co 0.05 ) 2 As 2 Fe 75 As Fe Fe Transferred hyperfine field from nn >> dipolar field Fe Each 75 As has at least one magnetic Fe among its 4 nn Coexistence at the microscopic scale No phase separation Checkerboards, etc. unlikely Coexistence at the atomic scale

22 Spin dynamics above T SDW 80 MHJ et al., arxiv: /T 1 (ms -1 ) As NMR T (K) Sharp transition ( T SDW = 5 K) No critical slowing down No glassiness (same T SDW as in neutron scattering) Unlike LSCO, well-defined features (despite 5% Co doping)

23 75 As NMR in BaFe 2 As 2 (undoped) +H int -H int NMR width is extremely sensitive to ~1% of impurities in BaFe 2 As 2 Kitagawa, Baek, MHJ (unpublished)

24 Disordered vs. incommensurate magnetic structure F.L. Ning et al. x=0.04 x=0.05 our work x=0.06 Large distribution Inhomogeneity at long distances Y. Laplace et al., arxiv:

25 Magnetic inhomogeneity above T SDW 0.6 (T 1 T) -1 (s -1 K -1 ) As NMR 67 K 99 K 161 K MHJ et al., arxiv: f (MHz) NMR intensity (a.u.) 75 As NMR H (T)

26 Nanoscale doping inhomogeneity

27 75 As NMR in Ba 0.6 K 0.4 Fe 2 As 2 Ba 0.6 K 0.4 Fe 2 As 2 Stronger magnetic and lattice inhomogeneity than for 5% Co

28 75 As NMR in Ba 0.6 K 0.4 Fe 2 As 2 ρ ab (µω m) Fe/Co Ba 0.6 K 0.4 Fe 2 As 2 75 T1-1 (ms -1 ) I NMR (arb. u.) di/dt Regions without SDW (>40% volume) SC regions Inhomogeneous coexistence in this 40% K-doped sample

29 SC-SDW coexistence in Co & K doped pnictides «Homogeneous» (microscopic or atomic scale) in Co-doped BaFe 2 As 2 Not clear in K-doped BaFe 2 As 2 Electronic inhomogeneity is present in both systems. Relevant?