Electronic inhomogeneity, magnetic order & superconductivity probed by NMR in cuprates and pnictides Marc-Henri Julien Laboratoire de Spectrométrie Physique Université J. Fourier Grenoble I
Acknowledgments NMR @ 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)
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)
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.
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
139 La NMR in La 2-x Sr x CuO 4 (1998-1999, the second youth of LSCO)
Magnetic transition
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)
Magnetic volume fraction 100% of the La nuclei experience spin freezing 1/T 1 (s -1 ) 30 20 10 139 La NMR La 1.88 Sr 0.12 CuO 4 0 0 20 40 60 80 100 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
Revised phase diagram of LSCO La 2-x Sr x CuO 4
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
Disordervs. stripe physics
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)
Inhomogeneous magnetism / cluster spin-glass 1/T 1 (s -1 ) 30 20 10 139 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 0 0 20 40 60 80 100 T (K) NMR Signal (a.u.) La 1.94 Sr 0.06 CuO 4 LSCO x=0.06 63 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 -3-2 -1 0 1 2 K total (%) M.-H. J et al., PRL (1999)
Nanoscale doping inhomogeneity
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 ) 10 2 10 1 10 0 pristine disordered Magnetic transition shifts to lower T Consistent with ~1% planar defects σ log 10-1 2 1 Magnetic distribution mostly unaffected 0 0 20 40 60 80 100 T (K)
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
Pnictide zoology
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 0 20 40 60 80 T (K)
75 As NMR in Ba(Fe 1.95 Co 0.05 ) 2 As 2 MHJ et al., arxiv:0906.3708 ρ ab (µω m) 5 4 3 2 1 S C SDW 0 I NMR (a.u) 2 Paramagnetic resonance position 1 S C SDW Skin effect 0 0 50 100 150 200 250 T (K) 100% of the 75 As nuclei experience magnetic order
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
Spin dynamics above T SDW 80 MHJ et al., arxiv:0906.3708 1/T 1 (ms -1 ) 60 40 20 75 As NMR 0 0 100 200 300 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)
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)
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:0906.2125
Magnetic inhomogeneity above T SDW 0.6 (T 1 T) -1 (s -1 K -1 ) 0.5 0.4 0.3 0.2 0.1 75 As NMR 67 K 99 K 161 K MHJ et al., arxiv:0906.3708 0.0 105.74 105.76 105.78 105.80 f (MHz) NMR intensity (a.u.) 75 As NMR 14.0 14.2 14.4 14.6 14.8 15.0 H (T)
Nanoscale doping inhomogeneity
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
75 As NMR in Ba 0.6 K 0.4 Fe 2 As 2 ρ ab (µω m) 4 2 0 Fe/Co Ba 0.6 K 0.4 Fe 2 As 2 75 T1-1 (ms -1 ) I NMR (arb. u.) 2 1 0 100 50 di/dt 40 20 0 50 100 150 0 0 50 100 150 200 250 Regions without SDW (>40% volume) SC regions Inhomogeneous coexistence in this 40% K-doped sample
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?