Phase Diagram of Pnictide Superconductors. Interplay between magnetism, structure, and superconductivity. B. Büchner

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1 Phase Diagram of Pnictide Superconductors Interplay between magnetism, structure, and superconductivity B. Büchner Institut für Festkörperforschung IFW Dresden

2 High Temperature Superconductivity in FeAs Compounds OUTLINE Introduction Phase Diagram of LaFeAsO 1-x F x (and other pnictides) Structural, magnetic, and superconducting transitions Superconducting State Gap, penetration depth, relaxation rate Normal State Properties Electronic Structure (XAS, PES, ARPES) Pseudogap (NMR, χ) Electronic transport and spin fluctuations Charge inhomogeneity (NQR) Tuesday

3 Superconductivity in La(O 1-x F x )FeAs: The initiation Y. Kamihara et al., J. Am. Chem. Soc. 130, 3296 (2008) Februrary 2008 Picture: H. Takahashi et al., Nature 453, 376 (2008) Dec. 2008: More than 600 papers on pnictide superconductors

4 Transition temperature (K) Superconductivity above 50 K Year of discovery C. Hess et al., EPL (2009) similar data: e.g. Ren et al. Chin Phys. Lett. 2008

5 Superconductivity above 50 K La. Sm Gd 4πχ 4πχ (0h) FC ZFC T (K) FC ZFC 2 (0.5h) T (K) FC ZFC 5 (6h) FC ZFC 6 (12h) πχ 4πχ 0.0 FC FC 0.0 4πχ ZFC 3 (1.5h) ZFC 7 (24h) πχ 4πχ FC ZFC 4 (3h) GdFeAsO 0.83 F 0.17 SE 1778/1-7 Milling Experiment B = 20G S. Wurmehl et al, work in progress T (K)

6 Fe pnictides: A class of high T c superconductors 1111 systems La, Ce Gd-based F, O doped F doped REOFeAs O defici. REOFeAs Sm doped SrFFeAs 122 systems Ba, Sr, Eu, Ca- based K, Na, Co doped T c up to 39 K Intermetallic comp. Single crystals M. Rotter, M. Tegel, and D. Johrendt PRL 2008

Fe pnictides: A class of high T c superconductors 0 FC χ (% (4π) 1 ) -10-20 -30 1111 systems BaAs 2 Fe 1.9 Co 0.1 SE 1737 A La, Ce Gd-based F, O doped B = 20G ZFC F doped REOFeAs O defici.

7 Fe pnictides: A class of high T c superconductors 0 FC χ (% (4π) 1 ) systems BaAs 2 Fe 1.9 Co 0.1 SE 1737 A La, Ce Gd-based F, O doped B = 20G ZFC F doped REOFeAs O defici. REOFeAs Sm doped SrFFeAs T (K) 122 systems Ba, Sr, Eu, Ca- based K, Na, Co doped T c up to 39 K Intermetallic comp. Single crystals M. Rotter, M. Tegel, and D. Johrendt PRL 2008

8 Fe pnictides: A class of high T c superconductors 1111 systems La, Ce Gd-based F, O doped F doped REOFeAs O defici. REOFeAs Sm doped SrFFeAs 122 systems Ba, Sr, Eu, Ca- based K, Na, Co doped T c up to 39 K Intermetallic comp. Single crystals M. Rotter, M. Tegel, and D. Johrendt PRL 2008

9 Fe pnictides: A class of high T c superconductors 1111 systems La, Ce Gd-based F, O doped F doped REOFeAs O defici. REOFeAs Sm doped SrFFeAs 122 systems Ba, Sr, Eu, Ca- based K, Na, Co doped T c up to 39 K Intermetallic comp. Single crystals M. Rotter, M. Tegel, and D. Johrendt PRL 2008 Medvedev, Felser et al., Nature Materials 2009

10 Interplanar distance may differ very much! LaO 1-x F x FeAs 1111 FeSe 1-x Te x (Fe 2 P 2 )(Sr 4 Sc 2 O 6 ) T C, max = 17 K H. Ogino et al., arxiv:

REOFeAs Sm doped SrFFeAs 122 systems Ba, Sr, Eu, Ca- based K, Na, Co

11 Fe pnictides: A class of high T c superconductors 1111 systems La, Ce Gd-based F, O doped F doped REOFeAs O defici. REOFeAs Sm doped SrFFeAs 122 systems Ba, Sr, Eu, Ca- based K, Na, Co doped T c up to 39 K Intermetallic comp. Single crystals M. Rotter, M. Tegel, and D. Johrendt PRL 2008

12 Cuprates Magnetism and Superconductivity

13 Cuprates Magnetism and Superconductivity

14 Magnetism and Superconductivity Cuprates Heavy fermions CePd 2 Si 2 Mathur, Julian, Lonzarich et al. 1998

15 Magnetism and Superconductivity Cuprates Heavy fermions CePd 2 Si 2 Mathur, Julian, Lonzarich et al. 1998

16 High Temperature Superconductivity in FeAs Compounds OUTLINE Introduction Phase Diagram of LaFeAsO 1-x F x (and other pnictides) Structural, magnetic, and superconducting transitions Superconducting State Gap, penetration depth, relaxation rate Normal State Properties Electronic Structure (XAS, PES, ARPES) Pseudogap (NMR, χ) Electronic transport and spin fluctuations Charge inhomogeneity (NQR)

17 Some of the IFW involved in the research on FeAs Synthesis: G. Behr, J. Werner, S. Singh, C. Nacke, S.Wurmehl et al. M, Thermodynamics: N. Leps, L. Wang, R. Klingeler et al. NMR, ESR: H. Grafe, G. Lang. F. Hammerath, V. Kataev et al. Transport : X-ray diffraction: Spectroscopy: A. Kondrat, G. Friemel, C. Hess et al. J. Hamann-Borrero S. Borysenko, D.V. Evtushinsky, A. Koitzsch, J. Geck A. Kordyuk, V.B. Zabolotnyy, T. Kroll, M. Knupfer et al. Cooperations μsr, Mößbauer H.H.Klauss, H. Maeter et al. TU Dresden μsr H. Luetkens, R. Khasanov et al. PSI Villingen Crystals C.T. Lin, D. Inosov, V. Hinkov, B. Keimer et al. MPI FKF Stuttgart NMR N. Curro UC Davis X-ray/neutron diffraction M. Braden et al. U Köln X-ray/neutron diffraction R. Feyerherm, D. Argyriou et al. HZ Berlin DFG-Research Unit FOR538 Doping Dependence of Phase Transitions and Ordering Phenomena in Copper-Oxygen Superconductors

18 Resistivity and Susceptibility of La(O 1-x F x )FeAs

19 Preparation & Characterization LaO 1-x F x FeAs, x= Phase purity... Lattice constants...

20 Preparation & Characterization LaO 1-x F x FeAs, x= Fluorine content... Lattice constants...

21 Resistivity of La(O 1-x F x )FeAs

22 Two phase transitions in LaOFeAs H.-H. Klauss et al., PRL 101, (2008)

23 LaOFeAs: Competing OP above T S? Lattice constant (Å) XRD c b a Cmma P4/nmm dt dp N = TV negative! Δα Δc p α (10-6 K -1 ) Thermal Expansion T (K) specific heat anomaly Δc p (J/molK) at T S : upturn truncated V S T p p T positive pressure dependence! L. Wang et al., arxiv:

24 α (10-6 /K) T s LaOFeAs Thermal Expansion large fluctuation region at T>T S M/B (10-4 emu / mol) ρ (mω cm) T N T (K) Magnetisation: linear T-dependence at high T, only weak changes due to fluctuations Resistivity Peak at T S enhanced scattering in the fluctuation regime Strong link between electronic and structural degrees of freedom Wang et al., subm. to PRB

25 Two phase transitions in (Pr,Sm)OFeAs T N T S (220) SmOFeAs Kimber et al., PRB (2008) Structural Transition similar for all RE No transition in doped systems (x ~0.1)

26 REOFeAs: Structural changes Thermal expansion α(10-5 /K) 1.2 LaFeAsO PrFeAsO T Pr N GdFeAsO T N T μ N T S T S CeFeAsO SmFeAsO T N T N T S T S T(K) Thermal expansion α(10-5 /K) T N T S B = T(K) R. Klingeler et al., 2009, in print

27 REOFeAs: Structural changes Thermal expansion α(10-5 /K) 1.2 LaFeAsO PrFeAsO T Pr N GdFeAsO T N T μ N T S T S CeFeAsO SmFeAsO T N T N T S T S T(K) Thermal expansion α(10-5 /K) T N T S T(K) B = 0 B = 9T

28 Phase transitions in undoped 122 compounds BaFe 2 As 2 SrFe 2 As 2 D. Johrendt and R. Pöttgen, Physica C 2009 A. Jesche et al., PRB 2008

29 SDW magnetism in SrFe 2 As 2 Krellner et al., PRL `08, arxiv:

30 Resistivity of Ba 1-x K x Fe 2 As ,5x10 2,0x10-2 3,0x10-1 2,5x10-1 Ba(FeAs)2, thin piece up- curve K 1,8x10-2 1,6x10-2 1,4x10-2 ρ [mωcm] 2,0x10-1 1,5x10-1 1,0x10-1 5,0x10-2 0, T[K] 1,2x10-2 1,0x10-2 8,0x10-3 6,0x10-3 4,0x10-3 2,0x10-3 0,0 dρ/dt [mωcm/k] M. Rotter et al., Ang. Chem. 2008

31 Magnetic order of LaOFeAs T= 13 K 57 Fe Mössbauer spectroscopy counts (arb. units) T= 78 K _ T= 126 K well defined magnetic hyperfine field commensurate magnetic order below 138 K B hyp (T 0) ~ 4.86 T ordered moment ~ 0.3 µ B itinerant magnet T= 137 K LaOFeAs velocity (mm/s) H.-H. Klauss et al., PRL 101, (2008)

Eremin, PRB 78, 140509(R) (2008) I. Mazin et al.

32 Magnetic order of LaOFeAs C. de la Cruz, et al., Nature 453, 899 (2008) M. Korshunov, I. Eremin, PRB 78, (R) (2008) I. Mazin et al., PRL 101, (2008) J. Dong et al., EPL 83, (2008) K. Kuroki et al., PRL 101, (2008) S. Raghu et al., PRB (2008)

33 Magnetic order parameter in undoped LaOFeAs Four band SDW theory U=0.26eV J=U/5 Q AFM = (π,π) Δ SDW (0) = 31 mev µ= 0.33 μ B See: M. Korshunov and I. Eremin arxiv: H.-H. Klauss et al., PRL 101, (2008)

34 T N LaOFeAs T S S x=0: Stuctural and SDW Transistions = ln ε Resistivity Peak at T S ρ 1, λ enhanced scattering at higher T Inflection point at T N reduced scattering + localization at T<T N Thermopower S Sign change at T N ( σ( ε) ) ln λ = + ε ln A ε 0 π π π electrons 1 n 0 π holes

35 T N LaOFeAs T S S x=0: Stuctural and SDW Transistions = ln ε Resistivity Peak at T S ρ 1, λ enhanced scattering at higher T Inflection point at T N reduced scattering + localization at T<T N Thermopower S Sign change at T N ( σ( ε) ) ln λ = + ε ln A ε 1 n Consistent with gapping of electron-like FS electrons holes

36 T N LaOFeAs T S S x=0: Stuctural and SDW Transistions = ln ε Resistivity Peak at T S ρ 1, λ enhanced scattering at higher T Inflection point at T N reduced scattering + localization at T<T N Thermopower S Sign change at T N ( σ( ε) ) ln λ = + ε ln A ε 1 n Consistent with gapping of electron-like FS electrons Hall-Effect: More negative at T<T N π holes McGuire et.al. PRB 78, (2008) R H 2 e pμ nμ = q n 2 h ( μ + pμ ) 2 e h 0 π π 0 π

37 T N LaOFeAs T S S x=0: Stuctural and SDW Transistions = ln ε Resistivity Peak at T S ρ 1, λ enhanced scattering at higher T Inflection point at T N reduced scattering + localization at T<T N Thermopower S Sign change at T N ( σ( ε) ) ln λ = + ε ln A ε 1 n Consistent with gapping of electron-like FS Hall-Effect: More negative at T<T N electrons holes McGuire et.al. PRB 78, (2008) R H 2 e pμ nμ = q n 2 h ( μ + pμ ) 2 e h Consistent with gapping of hole-like FS

38 T N LaOFeAs T S S x=0: Stuctural and SDW Transistions = ln ε Resistivity Peak at T S ρ 1, λ enhanced scattering at higher T Inflection point at T N reduced scattering + localization at T<T N Thermopower S Sign change at T N ( σ( ε) ) ln λ = + ε ln A ε 1 n Consistent with gapping of electron-like FS Hall-Effect: More negative at T<T N electrons holes McGuire et.al. PRB 78, (2008) R H 2 e pμ nμ = q n 2 h ( μ + pμ ) 2 e h Consistent with gapping of hole-like FS Work in progress...

39 Resistivity of ReOFeAs Resistivity Peak at T S enhanced critical scattering Inflection point at T N reduced scattering + gap opening at T<T N ρ 1 n, 1 λ Rare earth influence: induced in-gap states? C.Hess et al., arxiv: Kimber et al., PRB 08

40 ROFeAs (R = La, Pr, Ce, Sm) ZF-μSR: Zero Field Muon Spin Rotation Static magnetic order below T N 100% magnetic volume fraction Commensurate magnetic structure H. Maeter, et al., arxiv: (2009). T-dependence of μsr frequency Second order transition at T N (Fe) T N (R) Why is CeOFeAs different? Moessbauer: Moessbauer spectroscopy All compounds possess the same ordered Fe moment (~0.35 μ B )! Neutron scattering: μ B? M. A.McGuire et al., New J. Phys. 11, (2009).

41 Ce magnetization above T N Ce CeOFeAs Magnetization in molecular field of the Fe sublattice Contributes to the same magnetic Bragg peak as the Fe order Creates a field at the muon site which is proportional to the Ce magnetization This can be modeled by: a Curie-like term to the μsr frequency a calculation of thermal population of crystal electric field (CEF) levels f T ) = f ( 0 1 T T N α Fe sublattice magnetization γ ~ C 1 + T Θ Curie-like Ce magnetization H. Maeter, et al., arxiv: (2009). S. Chi et al., arxiv: (2008).

Interplay of Rare Earth and FeAs electronic systems LDA band structure CeOFeAs PrOCeAs Strong hybridization between Fe and Ce states CeOFeP is a moderate

42 Interplay of Rare Earth and FeAs electronic systems LDA band structure CeOFeAs PrOCeAs Strong hybridization between Fe and Ce states CeOFeP is a moderate heavy fermion system L. Pourovskii et al., EPL (2008) Pr states shifted 2 ev downwards E. M. Brüning et al., Phys. Rev. Lett. 101, (2008)

43 Resistivity of La(O 1-x F x )FeAs

44 Magnetism of lightly doped La(O 1-x F x )FeAs H. Luetkens et al., Nature Materials 2009

45 Magnetism of lightly doped La(O 1-x F x )FeAs H. Luetkens et al., Nature Materials 2009

46 Doping effect: LaFeAsO 1-x F x Thermal expansion α(10-5 /K) LaO 1-x F x FeAs x= T(K)

47 Doping effect: LaFeAsO 1-x F x Thermal expansion α(10-5 /K) LaO 1-x F x FeAs x=0.00 x= T(K)

48 Doping effect: LaFeAsO 1-x F x Thermal expansion α(10-5 /K) LaO 1-x F x FeAs x=0.00 x=0.02 x= T(K)

49 Doping effect: LaFeAsO 1-x F x Thermal expansion α(10-5 /K) LaO 1-x F x FeAs x=0.00 x=0.02 x=0.04 x= T(K)

Doping effect: LaFeAsO 1-x F x Thermal expansion α(10-5 /K) 1.4 1.2 1.0 0.8 0.6 0.

50 Doping effect: LaFeAsO 1-x F x Thermal expansion α(10-5 /K) LaO 1-x F x FeAs x=0.00 x=0.02 x=0.04 x=0.05 x= T(K)

51 Phase diagram of LaFeAsO 1-x F x 200 LaFeAsO 1-x F x dv/dt>0 T (K) 150 orthorh. tetragonal T C from χ(t), μsr SDW magnetic order T N from χ(t), μsr T S from χ(t), α(t) T* from α(t) dt N /dp<0 Superconductivity Nominal F-content L. Wang et al., arxiv:

52 Superconductivity of La(O 1-x F x )FeAs

53 Phase Diagram of La(O 1-x F x )FeAs H. Luetkens et al., Nature Materials 2009

54 Phase Diagram of La(O 1-x F x )FeAs H. Luetkens et al., Nature Materials 2009

) does not change the structural distortion, but a few percent Flourine (electron doping) completely

55 Phase Diagrams of CeFeAsO 1-x F x and SmFeAsO 1-x F x CeO 1-x F x FeAs Zhao et al., Nature Materials (2008), neutrons 100 % rare earth doping (5% lattice constant change!) does not change the structural distortion, but a few percent Flourine (electron doping) completely suppresses T s! gradual decrease of FeAs Neel temperature to zero? coexistence of magnetism and superconductivity? Yes Drew et al., Nature Materials 2009

56 Resistivity CeO 1-x Fe x As Tetragonal Orthorombic structural transition via synchrotron XRD 0 % 5 % (220) (006) 10 % 15 % superconducting 25 % J. E. Hamann-Borrero, A. Kondrat et al., in preparation

57 Zero field μsr: : CeO 1-x Fe x As magnetic volume fraction CeO 1-x F x FeAs 100% 80% 60% 40% 20% 0% zero field μsr temperature (K) undoped 5% F-content 10% F-content 15% F-content 50% Determine T N (Fe) from magnetic volume: e.g.50% of signal shows static relaxation Strong reduction of T N for x>0! Appearance of µsr frequency Long range coherent sublattice magnetization Strong reduction of sublattice magnetization for x>0 µsr frequency (MHz) temperature (K) H. Maeter, et al., in preparation. No long range order for x=0.15 but short range magnetic order present with f µ (T)=0! Mean sublattice magnetization = 0 not visible in neutron scattering

58 Transverse field μsr: : CeO 1-x Fe x As Static magnetic order local field (G) CeO 1-x F x FeAs 25% F-content 20% F-content 15% F-content temperature (K) 700 G TF-μSR T C Frequency shift Additional diamagnetic frequency shift Bulk superconductivity T C Bulk static magnetism for 15%! relaxation rate σ S (1/µs) 2,0 1,8 1,6 1,4 1,2 1,0 0,8 0,6 0,4 0,2 0,0 CeO 1-x F x FeAs 25% F-Content 20% F-content 15% F-content 700 G TF-μSR temperature (K) Static line width Bulk superconductivity T C Bulk static magnetism for 15%! H. Maeter, et al., in preparation.

59 CeO 1-x F x FeAs: coexistence of magnetism and SC? Zhao et al., Nature Materials (2008), neutrons Evidence for coexistence! XRD, ρ, µsr,... H. Maeter, et al., in preparation.

60 Phase Diagrams of doped BaFe 2 As 2 BaFe 2-x Co x As 2 Ba 1-x K x Fe 2 As 2 Chu et al., PRB 2009 Rotter et al., Ang. Chem. 2008

61 Pressure induced Superconductivity in (Ba,Sr)Fe 2 As 2 Colombier et al., arxiv.org/abs/ v1

62 Resistivity of La(O 1-x F x )FeAs

63 Phase Diagram of Ba 1-x K x Fe 2 As 2 Ang. Chem. 2008

64 Resistivity of doped pnictides SmO 1-x F x FeAs highest T c Rotter et al., Ang. Chem C. Hess et al., EPL (2009)

65 Resistivity of Co doped pnictides 2,0x10-6 5,0x10-6 Ba(Fe 0.95 Co 0.05 ) 2 As 2 4,0x10-6 1,5x10-6 Ca(Fe 0.94 Co 0.06 )2As 2, SE1754 cooling ρ (Ωm) 3,0x10-6 2,0x10-6 ρ [Ωm] 1,0x10-6 5,0x10-7 1,0x10-6 0, T in K Single crystals 0, T[K] ,0x ,0x10 1,0x10-7 1,5x10-6 CaFe 1.85 Co 0.15 As 2, SE1795D heating Ca(Fe 0.95 Co 0.05 ) 2 As 2, SE1781B cooling, 2mA 5,0x10-8 2,0x10-8 2,0x10-6 1,0x10-6 ρ [Ωm] 1,0x10-6 0,0-5,0x10-8 dρ/dt [Ωm/K] ρ [Ωm] 5,0x10-7 0,0-1,0x10-7 T c =21.2 K 0, T[K] 0, T[K] -2,0x10-8

Resistivity at the stuctural and SDW transistions LaOFeAs T S ρ 1 n 1, λ Resistivity Peak at T S enhanced scattering at higher T Inflection point at T N reduced scattering 5,0x10-6 Ba(Fe 0.95 Co 0.

66 Resistivity at the stuctural and SDW transistions LaOFeAs T S ρ 1 n 1, λ Resistivity Peak at T S enhanced scattering at higher T Inflection point at T N reduced scattering 5,0x10-6 Ba(Fe 0.95 Co 0.05 ) 2 As 2 4,0x10-6 Resistivity in Co doped systems ρ (Ωm) 3,0x10-6 2,0x10-6 1,0x10-6 Single crystal!! Reduction of scattering at T N smaller Mean free path limited by disorder due to Co atoms!! 0, T in K Intrinsic sources of scattering masked by disorder in Co doped single crystals!!!

67 High Temperature Superconductivity in FeAs Compounds OUTLINE Introduction Phase Diagram of LaFeAsO 1-x F x (and other pnictides) Structural, magnetic, and superconducting transitions Superconducting State Gap, penetration depth, relaxation rate Normal State Properties Electronic Structure (XAS, PES, ARPES) Pseudogap (NMR, χ) Electronic transport and spin fluctuations Charge inhomogeneity (NQR)

68 Superconducting Order Parameter (Gap)

69 How can we measure the superfluid density? via the magnetic penetration depth λ n s / m* is proportional to 1/ λ 2 Superconductivity in La(O 1-x F x )FeAs measure λ in vortex state of type II superconductor via field profile p(b) transverse field µsr B ext In anisotropic powder superconductors P(B) shows Gaussian shape 2 4 ΔB λ ab

70 How can we measure the superfluid density? via the magnetic penetration depth λ n s / m* is proportional to 1/ λ 2 measure λ in vortex state of type II superconductor via field profile p(b) transverse field µsr Superconductivity in La(O 1-x F x )FeAs 1,0 CeO B 0.75 F 0.25 FeAs ext 50 K 1.6 K muon spin polarization 0,5 0,0-0,5-1,0 0,0 0,2 0,4 0,6 0,8 1,0 1,2 In anisotropic powder superconductors P(B) shows Gaussian shape 2 4 ΔB λ ab time (µs)

71 Penetration Depth of La(O 1-x F x )FeAs Proximity of Magnetism? H. Luetkens et al., PRL 101, (2008)

72 Penetration Depth of La(O 1-x F x )FeAs T dependence of λ: consistent with BCS s-wave B dependence of λ: not simple s-wave: d, ext. s, multiband H. Luetkens et al., PRL 101, (2008)

73 Superconducting Properties of Co doped Ba FC T c = 23.0(2)K 4πχ BaFe 1.8 Co 0.2 As 2 BKZ 8 B = 20G μsr: no trace of magnetism -1.2 Bridgeman ZFC H. Luetkens, C. Nacke et al., in preparation

74 Superconductivity of Co doped Ba122 TF-μSR Superfluid density (full line shape analysis) for field applied in different direction. Pronounced anisotropy of the penetration depth λ. Assuming λ a = λ b one can calculate the low temperature values: λ a (T=0) = 220 nm λ c (T=0) = 1100 nm H. Luetkens, C. Nacke et al., in preparation

75 Superconductivity of Co doped Ba122 TF-μSR

volumes ~ 2 stronger temperature dependence of λ -2

76 Superconductivity in Ba 1-x K x Fe 2 As 2 µsr: Phase separation into commensurate SDW and superconducting volumes ~ 2 stronger temperature dependence of λ -2 large and small gap? μsr: 50 % non-magnetic R. Khasanov, PRL 09

77 Gap on the inner Г-barrel, ГM cut1 4 Intensity (arb. u.) K 15 K 20 K 25 K 30 K 35 K 40 K 45 K fit Δ (mev) Resistance (arb. u.) T (K) T c =32 K ω (mev) D.V. Evtushinsky et al., PRB 2009

78 Anisotropy of Gap according to ARPES D.V. Evtushinsky et al., PRB 2009 Similar results see eg. Ding et al EPL 2008

79 Penetration Depth of Ba 1-x K x Fe 2 As 2, T c = 32 K Δ large: 9 mev (ARPES) Δ small 1.1 mev (ARPES: < 4 mev) D.V. Evtushinsky et al., New J. Phys. 2009

80 Penetration Depth and Uemura Plot Uemura plot: T C scales linearly with the superfluid density, i.e. T C 1/ λ 2 n s /m* Bi2223 h-doped cuprates T C (K) LN 2 La214 Y123 e-doped cuprates SLCO La-Fx This work Nd-O0.85 This work Sm-O0.85 This work La-F0.08 Carlo et al. Ce-F0.16 Carlo et al. Nd-F0.12 Carlo et al. Sm-F0.18 Drew et al. 20 PCCO NCCO λ -2 ab (μm-2 ) The Fe-based superconductors are close to the Uemura line for hole doped cuprates hope for higher T c in the future

81 Gap and Spin Lattice Relaxation Rate (NMR)

82 75 As NMR on La(O 1-x F x )FeAs: T 1 No Hebel Slichter coherence peak, no expon. decay T 3 dependence below T c is indicative for line nodes 10 H 0 c suggestive of d-wave superconductivity coherence peak and exp decay T 1-1 (s -1 ) T 3 T c 0.01 LaO 0.9 F 0.1 FeAs Temperature (K) H.-J. Grafe et al., PRL 101, (2008)

83 75 As NMR on La(O 1-x F x )FeAs: T 1 1 published data H ab peak new data H ab peak theory Parker & Mazin At low temperatures deviation from T 3 extended s +/- wave - scenario (s -1 ) 0.1 LaO 0.9 F 0.1 FeAs Mazin et al., PRL 101, (2008). T 1-1 * Parker et al. PRB Chubukov et al. PRB 2008 T 3 1E Temperature (K) or dirty d-wave

84 75 As NMR on La(O 1-x F x )FeAs: T T c ~T 3 ~T 1 (s -1 ) T 1-1 0,1 0,01 ~T LaO 0.9 F 0.1 FeAs 1E-3 ~T T (K) LaO 0.9 F 0.1 FeAs 1-γ

85 75 As NMR on La(O 1-x F x )FeAs: T ~T 3 (s -1 ) 10 1 T c Intensity (a.u.) ~T T 1-1 0,1 0,01 ~T LaO 0.9 F 0.1 FeAs 1E-3 ~T T (K) LaO 0.9 F 0.1 FeAs 1-γ

86 75 As NMR on La(O 1-x F x )FeAs: T ~T 3 As-deficiency 10 T c ~T 1 disorder T 1-1 (s -1 ) 0,1 0,01 ~T LaO 0.9 F 0.1 FeAs but: higher T c higher B c2 (0) 1E-3 ~T T (K) LaO 0.9 F 0.1 FeAs 1-γ T < T c : T 1-1 ~ T 4.8 T << T c : T 1-1 ~ T

87 75 As NMR on La(O 1-x F x )FeAs: T T c ~T 3 ~T 1 (s -1 ) T 1-1 0,1 0,01 ~T LaO 0.9 F 0.1 FeAs 1E-3 Scenarios: ~T T (K) LaO 0.9 F 0.1 FeAs 1-γ Transition from s +/- to conventional s +/+ state due to impurities As deficiencies cause mainly intraband scattering and further protect the unconventional s +/- state (higher T c, higher H c2 ) ( smart impurities ) F. Hammerath, H.-J. Grafe, S.L. Drechsler, I. Eremin et al.

88 75 As NMR on La(O 1-x F x )FeAs: T T c ~T 3 ~T 1 (s -1 ) T 1-1 0,1 0,01 ~T LaO 0.9 F 0.1 FeAs 1E-3 Scenarios: ~T T (K) LaO 0.9 F 0.1 FeAs 1-γ Fuchs et al, PRL 2008 Transition from s +/- to conventional s +/+ state due to impurities As deficiencies cause mainly intraband scattering and further protect the unconventional s +/- state (higher T c, higher H c2 ) ( smart impurities ) F. Hammerath, H.-J. Grafe, S.L. Drechsler, I. Eremin et al.

89 SC transition in GdFeAsO 0.85 F 0.15 : Strange and Puzzling behavior 10 α (10-6 / K) C p (J / mol K) T 0T T (K)

90 SC transition in GdFeAsO 0.85 F 0.15 α (10-6 / K) C p (J / mol K) T 0T specific heat c p (J / mol K) PrFeAsO 0.85 F 0.15 T C ~41K B=0 B=9T c p /T (J / mol K 2 ) T (K) T (K) Δc p =0.53 J/mol K T c = 41.2K T (K)

91 SC transition in GdFeAsO 0.85 F 0.15 α (10-6 / K) C p (J / mol K) T C 20K T N Gd = 2.9K 0T T (K) 0T SC transition visible Δc p, SC = 2.0 J / (mol K) BCS theory: γ = Δc/(1.43 T c ) 70 mj/(molk) dt dp C = TV 1.4 Δα Δc K GPa p

92 SC transition in GdFeAsO 0.85 F 0.15 α (10-6 / K) C p (J / mol K) T C 20K T N Gd = 2.9K 0T 0T Relaxation rate (μs -1 ) GdO 0.85 FeAsF T C T (K) T (K)

93 GdFeAsO 0.85 F 0.15 : Specific heat 50 GdFeAsO 0.85 F 0.15 C p (J / mol K) B=9T B=0 B dependence of c p magnetic fluctuations? T (K)

94 GdO 1-x F x FeAs Gd HF-ESR: Width of the signal Gd 3+ : 4f 7, L = 0; J = S =7/2 no coupling to lattice, probes spin degrees of freedom 2 1 x= K 160K inhomogeneous broadening absorption (a.u.) K 120K 100K 80K 60K 40K 20K Gd sees enhanced magnetism B (T)

95 Electron Spin Resonance of GdO 1-x F x FeAs g= undoped x= doped x= K 160K B res (T) High frequency/field ESR, F = 328GHz undoped x=0 doped x= absorption (arb. u.) K 120K 100K 80K 60K 40K 20K Temperature (K) Magnetic field (T) Superconductor (T c = 21 K): strong broadening and shift of the Gd-ESR response onset of inhomogeneous quasi-static spin correlations at T < 80 K

96 SC transition in GdFeAsO 0.85 F Thermal Expansion B = 0 Specific heat Thermal expansion α (10-6 /K) T B=0 5T 9T 13T 14T 16T T (K) B = 14T B = 0 9T 7T 5T 3T 0T T (K) 14T 13T 12T 11T 10T specific heat c p (J / mol K)

97 GdFeAsO 0.85 F 0.15 : Magnetostriction Magnetostriction β (10-6 ) K 20K 18K 15K 12K 10K 40K 8K B (T)

98 GdFeAsO 0.85 F B C2 ~20T B C2 >60T 15 B (T) 10 5 T c (B) thermal expansion T c (B) specific heat B c (T) magnetostriction LaFeAsO 0.9 F T(K) Fuchs et al, PRL 2008

99 SC transition in GdFeAsO 0.85 F 0.15 : Strange and Puzzling behavior 20 B C2 ~20T Unusually small H C2! What causes pair breaking? 15 B (T) 10 5 Superconductivity from thermal expansion from specific heat from magnetostriction T (K) Why large anomalies in c p, α? Enhanced magnetism 80K! Intrinsic inhomogeneities?

100 Spin lattice relaxation rate, T 1-1, normal state (T 1 T) -1 (s -1 K -1 ) pseudogap? 75 As NMR H 0 ab 0.05 LaO 0.9 F 0.1 FeAs Temperature (K) H.-J. Grafe et al., PRL 101, (2008) H.-J. Grafe et al., New J. Phys. 2009

101 High Temperature Superconductivity in FeAs Compounds OUTLINE Introduction Phase Diagram of LaFeAsO 1-x F x (and other pnictides) Structural, magnetic, and superconducting transitions Superconducting State Gap, penetration depth, relaxation rate Normal State Properties Electronic Structure (XAS, PES, ARPES) Pseudogap (NMR, χ) Electronic transport and spin fluctuations Charge inhomogeneity (NQR) Tuesday

More a progress report than a talk

More a progress report than a talk Superconductivity and Magnetism in novel Fe-based superconductors Ilya Eremin 1,2 and Maxim Korshunov 1 1 - Max-Planck Institut für Physik komplexer Systeme, Dresden, 2- Institut für Theoretische Physik,