Magnetic, structural and electronic properties of LaFeAsO1-xFx Rüdiger Klingeler Leibniz Inst. for Solid State and Materials Research IFW Dresden Today: Original Abstract: NMR mSR, M, r Pulsed field m-wave, M Optics Neutrons Magnetisation H. Grafe et al., PRL 101, 047003 (‘08) H.H. Klauss et al., PRL, in print H. Luetkens et al., PRL, accepted G. Fuchs et al., PRL, accepted A. Narduzzo et al., Phys. Rev. B, in print S.-L. Drechsler et al., arXiv:0805.1321 H. Luetkens et al., arXiv:0806.3533 S.A.J. Kimber et al. arXiv:0807.4441 R. Klingeler et al., arXiv:0808.0708

Our samples non-magnetic H. Luetkens et al., arXiv:0806.3533

LaFeAsO1-xFx C. Hess et al.

LaFeAsO1-xFx c(T) ~ T: AFM correlations? Sample degrades >500K R. Klingeler et al., arXiv:0808.0708

LaFeAsO1-xFx c(T) ~ T: pseudogap vs. AFM correlations Slope dc/dT const. AFM correlations in SC samples or: x-independent large pseudogap R. Klingeler et al., arXiv:0808.0708

LaFeAsO1-xFx c(T) ~ T: pseudogap vs. AFM correlations Slope dc/dT const. AFM correlations in SC samples or: x-independent large pseudogap R. Klingeler et al., arXiv:0808.0708

PrFeAsO: Thermal Expansion

PrFeAsO: Thermal Expansion La  Pr Field dependent structural changes below TN (no field effect in LaFeAsO)

Acknowledgements Cooperations: H.H. Klauss et al. TU Dresden B. Büchner Synthesis: G. Behr, J. Werner, M. Deutschmann, R. Müller, R. Pichl, … Theory: S.L. Drechsler, H. Eschrig, K. Koepernick, …. Transport : A. Kondrat, C. Hess et al. M, Thermodynamics: N. Leps, S. Gass, L. Wang et al. NMR: H. Grafe, G. Lang, D. Paar, V. Kataev et al. Diffraction: J. Hamann-Borrero Pulsed field: G. Fuchs et al. Microwave absorption: A. Narduzzo et al. Cooperations: H.H. Klauss et al. TU Dresden J. Litterst et al TU Braunschweig H. Luetkens et al. PSI Villingen A. de Visser et al. U Amsterdam M. Braden et al. U Köln I. Eremin et al. MPI PKS Dresden A. Vassiliev et al. Moscow State University

LaFeAsO: Pressure dependence Negative p-dependence of TN Coll.: M. Braden, U Köln A. De Visser, U. Amsterdam

Transport Resistivity Clearly two features in the second derivative Check with Christian T_dep something astonishingly similar to cuprates Clearly two features in the second derivative Anomaly at T = 150 K survives for x = 0.05 ~T2, ~T depending on doping and temperature

Susceptibility Phase Transition Kink around 140 K due to afm correlations Derivative shows two peak structure (magnetic and structural phase transition) Shift towards lower energies Decreasse of magnetization at the kink

Mößbauer/ZF-mSR Clear oscilations below TN Clear line splitting at TN AFM arises from a spin density wave of the conduction electrons Clear line splitting at TN Effective moment m=0.25mB << 2

mSR TF mSR, x = 0.1 ZF mSR, x = 0.1 Magnetism suppressed Relaxation rate s ~ l-2 ~ n/m* → lab(0) = 254 nm

Spin lattice relaxation NMR 75As, LaO0.9F0.1FeAs Knight shift Spin lattice relaxation Knight shift: 1) Pseudogap-like density suppression 2) Spin-singlet pairing T1-1 ~ T3 for T < Tc → line nodes

LaFeAsO1-xFx Weak localization-like behavior at low T for x<0.05 Superconductivity for x>0.04 Anomaly at T = 150 K for nonsuperconducting samples Maximum above Tc for sc samples remnant from upturn Change from linear T-dependence in the normal state to quadratic Tc decreases for high doping C. Hess et al.

LaFeAsO1-xFx R. Klingeler et al., arXiv:0808.0708